Chapter 1. Bipedal monkeys

Chimpanzee sets a starting point

The closest living (i.e. non-extinct) relatives of humans are chimpanzees. This is unequivocally evidenced by the data of comparative anatomy and molecular genetics, which we talked a little about in the Preface. Paleontological and comparative genetic evidence indicates that the evolutionary lineages leading to humans and chimpanzees split approximately 6–7 million years ago.

Chimpanzees are divided into two species: the common chimpanzee ( Pan troglodytes), living north of the great Congo River, and the pygmy chimpanzee, or bonobo ( Pan paniscus), living south of her. These species separated from each other no more than 1–2 million years ago, that is, much later than “our” human line separated from the ancestors of chimpanzees. It follows that both types of chimpanzees have the same degree of relatedness to humans.

Chimpanzees are very important to any popular account of human evolution because they set the starting point. Traits that both humans and chimpanzees share are less interesting to us than traits that only we share. This, of course, is not very logical and smacks of discrimination and xenophobia. Yet books on human evolution rarely begin with a discussion of the important question of why we don't have a tail.

This is of little interest to anyone, because chimpanzees also do not have a tail. And gorillas don't have tails, and orangutans don't, and gibbons don't. This is a common feature of all great apes. This is not our unique feature. We want to know why we are so, so special and completely, completely different from those shaggy and wild ones in the zoo.

The story of human evolution usually begins not with the loss of the tail, but with bipedalism - walking on two legs. It seems to be ours, purely human. True, gorillas, chimpanzees and bonobos also sometimes walk like this, although not very often (up to 5–10% of the time). But for everyone except us, such a gait is uncomfortable. Yes, there’s really no need: your arms are so long, you’re hunched over a little – and you’re already on all fours. Non-human apes find it easier to walk using their knuckles, fist, or palm.

The interest in bipedalism clearly shows that it is modern apes that set the starting point when discussing anthropogenesis. Today we are well aware that, beginning around 7 million years ago, a large and diverse group of bipedal apes lived and flourished in Africa. They had no larger brains than chimpanzees, and they were unlikely to be superior to chimpanzees in mental abilities. In a word, they were still quite “non-human”, but already bipedal. If at least one of the species of these monkeys - Australopithecus, Paranthropus, Ardipithecus - accidentally survived to this day (in some African “lost world” - why not?), our bipedality would inspire us no more than taillessness. And stories about anthropogenesis would begin with something else. Maybe from the manufacture of stone tools (2.6 million years ago). Or from the moment (just over 2 million years ago) when the brain began to grow.

But all these bipedal non-human apes, unfortunately, became extinct (except those that evolved into humans). And therefore we will not deviate from the accepted tradition and will start with bipedality. We will talk mainly about the history of that group of apes that includes us but does not include chimpanzees. We will call representatives of this “human” evolutionary line hominids (in the singular, hominid). In fact, there is no consensus among anthropologists regarding the classification and nomenclature (official group names) of extinct and modern apes. We will stick to one of the options, according to which hominids include all representatives of that branch of the evolutionary tree that separated from the ancestors of chimpanzees 6-7 million years ago and which includes all primates closer to humans than to chimpanzees. All representatives of this group have now become extinct, except for one single species Homo sapiens. But in the past there were quite a lot of them (see reference table).

Get up and go

Hominids appeared in Africa, and all of their early evolution took place there. The conjecture that the fossil ancestors of people lived precisely on the African continent was expressed by Darwin in his book “The Descent of Man and Sexual Selection,” published in 1871, 12 years after “The Origin of Species.” At that moment, when in the hands of scientists there was not yet a single bone of someone even remotely similar to the transitional link between ape and man, Darwin’s guess looked incredibly bold. That it was confirmed is perhaps one of the most impressive facts in the history of evolutionary biology. Darwin literally wrote the following: “The mammals living in every great region of the world are closely related to the fossil species of the same region. It is therefore possible that Africa in the past was inhabited by now extinct apes closely related to the gorilla and chimpanzee. Since these two species stand closest to man, it seems somewhat more likely that our early predecessors lived on the African continent than elsewhere." Simple, modest and brilliant.

Hominids are characterized by an important common feature - walking on two legs. There are at least as many different hypotheses explaining the transition to bipedalism as there are known reasons that prompt monkeys to sometimes rise to their feet. Monkeys walk vertically when crossing shallow bodies of water. Maybe our ancestors became bipedal because they spent a lot of time in the water? There is such a hypothesis. Male monkeys, when flirting with females, stand up to their full height and show their penis. Maybe our ancestors wanted to show their genitals all the time? There is such a hypothesis. Females sometimes walk on two legs, clutching the cub to their belly (if the cub is not sitting on the mother’s back, clinging to the fur). Maybe it was important for our ancestors to drag two babies at a time, so they freed up their hands? There is also such a hypothesis...

And that is not all. There is an assumption that our ancestors sought to increase the viewing range (which became especially important after leaving the forest for the savannah). Or reduce the surface of the body exposed to the sun's rays, again after going out into the savannah. Or it’s just become fashionable to walk like that – it’s cool and girls like it. This, by the way, is quite plausible: this could have happened due to the “Fisher escape” mechanism, which is discussed in the chapter “The Origin of Man and Sexual Selection.” How to choose the right one from this many ideas? Or are several correct at once? Hard to say. Entire articles and even books are devoted to arguments in favor of each of the listed hypotheses, but none of them have direct evidence.

In such cases, in my opinion, preference should be given to hypotheses that have additional explanatory power, that is, they explain not only bipedality, but at the same time some other unique features of hominids. In this case, we will have to make fewer controversial assumptions. Below we will discuss one of these hypotheses, which seems to me the most convincing. But first you need to take a closer look at the facts.

Traditionally, it was believed that the last common ancestor of humans and chimpanzees preferred to walk on all fours, much like chimpanzees do. They thought that this was the original (primitive) [the word “primitive” and its antonym “advanced” have a very clear meaning in biology. Primitiveness is relative. It is possible to talk about the primitive and advanced states of a trait only by comparing different organisms with each other. Primitive means more similar to what the common ancestor of the species being compared had] the method of locomotion was preserved in chimpanzees (as well as gorillas and orangutans), and in our evolutionary line it was replaced by bipedalism in connection with the exit from the forest to the open savannah. However, recently suspicions have arisen that perhaps the last common ancestor of humans and chimpanzees, if not bipedal, at least showed a greater tendency to walk upright than modern chimpanzees and gorillas. New paleoanthropological finds clearly hint at this possibility.

In recent years, fossils have been discovered in Africa of several very ancient hominids that lived around the same time as the split in the evolutionary lineages leading to chimpanzees and humans. The classification of these forms remains controversial. Although they are described as representatives of three new genera ( Sahelanthropus, Orrorin, Ardipithecus) some experts believe that some of them should have been combined with each other or with a later genus Australopithecus. In particular, it was proposed to combine Orrorin, Ardipithecus and several species of primitive australopithecus into the genus Praeanthropus. But these debates are not very interesting for us: in the end, call it what you want, the main thing is to understand what kind of creatures they were, how they lived and how they changed over generations.

The most interesting thing about these ancient hominids is that they all probably already walked on two legs (albeit not as confidently as we do), but they did not live in an open savannah, but in a not very dense forest or on a mixed landscape, where forested areas alternated with open ones. This, in principle, does not contradict the old theory that the development of bipedality was associated with gradual the transition of primordially forest inhabitants to life in open areas.

SAHELYANTHROPE [reference data for the hominid species mentioned in the text are summarized in the table on p. 449]. Among the most important recently discovered forms is Sahelanthropus tchadensis, described from the skull, several jaw fragments and individual teeth. All this was found in 2001–2002 in northern Chad by French anthropologists under the leadership of Michel Brunet. The skull was informally nicknamed Tumay, which in local parlance means "a child born before the dry season." Paleoanthropologists give such nicknames to their finds for advertising purposes. Unfortunately, no fragments of the postcranial skeleton [postcranial skeleton – the entire skeleton except the skull] It was not officially reported, although there are rumors that a fragment of the femur was also found. The age of the find is 6–7 million years. Toomai, in principle, does not contradict ideas about what the common ancestor of humans and chimpanzees might have looked like [although in many features of the skull Tumay resembles a gorilla (S. V. Drobyshevsky, personal communication)], and most importantly, he is quite suitable for this role due to his age. But he may end up being the earliest ancestor of the chimpanzee or gorilla, or a very early representative of “our” lineage, that is, the hominids. Tumay's brain volume is very small (approximately 350 cm3). Based on this feature, it does not stand out at all from other non-human apes.

Three features of Sahelyanthropus are of particular interest. The first is the position of the foramen magnum, which is shifted forward compared to other apes. Perhaps this means that Toumai already walked quite often on two legs, and therefore the spine was attached to the skull not from the back, but rather from the bottom. The second interesting point is that Sahelanthropus, judging by the accompanying fossil flora and fauna, lived not in an open savannah, but on the shores of an ancient lake, in a mixed landscape, where open areas alternated with forested ones. Fossil remains of lake, forest and savanna animals were found in the vicinity of Sahelanthropus. The third important sign is the small size of the fangs. They are comparable to the fangs of female chimpanzees, but much smaller than those of males. The size of the fangs in male apes allows one to judge certain aspects of social life (this will be discussed in more detail below in the section on Ardipithecus). But, since there is only one skull and we do not know what gender Toumai was, it is not worth drawing far-reaching conclusions from the small fangs.

The find showed that ancient hominids or similar forms were more widespread in Africa than previously thought: almost all previous finds were made in the so-called Great Rift Valley, which runs north to south in East and Southern Africa.

ORRORIN. Another important find is Orrorin tugenensis, found in 2000 in Kenya by French researchers led by Brigitte Senu and Martin Pickford. Nickname – Millennium man(millennial person), age – about 6 million years. This is also a form close to the common ancestor of humans and chimpanzees. As in the case of Sahelanthropus, bone material for this species is still fragmentary and scarce. However, professional zoologists and anthropologists are well aware of how much information about the structure of a mammal can be extracted even from a few scattered bones [there is a widely known story about how the great paleontologist Georges Cuvier, one bone at a time, accurately reconstructed the appearance of the entire animal. This, of course, is an exaggeration, but there is some truth here: different parts of the animal are interconnected, and therefore changes in some parts in many cases affect others. This is called the principle of correlation. However, it should not be absolute: within certain limits, different parts of the skeleton can change independently of each other]. The skull of Orrorin has not yet been found, but based on the structure of the hip, anthropologists have concluded that it walked on two legs. Judging by the accompanying fossil flora and fauna, the orrorin did not live in an open savanna, but in a dry evergreen forest. A handful of scattered teeth similar to those of later hominids were found. Among them is one fang (upper right). It is small, about the size of female chimpanzees.

In general, it became clear that upright walking was most likely mastered by our ancestors a very long time ago. Almost immediately after the division of the human and chimpanzee lines, representatives of “our” line were already walking on two legs. Or maybe this happened even earlier? What if the common ancestors of humans and chimpanzees already preferred to walk on their hind limbs, and the current style of chimpanzees walking on their knuckles evolved later? This assumption is hampered by the fact that gorillas and orangutans also rely on their hands when walking. If we assume that bipedality was the original, primitive state for the ancestors of chimpanzees, then we will have to admit that subsequently representatives of this evolutionary line, independently of gorillas, acquired a gait very similar to a gorilla. There is nothing incredible about this. True, biologists, whenever possible, try to avoid assumptions about the independent appearance of the same trait in different evolutionary lines. This is called the principle of parsimony, or economy of hypotheses. But in this case, according to many anthropologists, this principle does not work: most likely, “knuckle walking” actually developed independently in orangutans, gorillas and chimpanzees.

ORANGUTANS WALK LIKE PEOPLE. Lately, there is growing evidence indicating that bipedal walking may not be derived from the knuckle-walking manner of chimpanzees and gorillas.

From what then can we derive it? Perhaps from those methods of movement that apes developed at the stage of life in the trees. For example, it was recently shown that the way that orangutans walk most closely to human gait is on two legs, holding onto branches with their hands.

The idea has already been expressed that the skeleton and muscles of our ancestors turned out to be preadapted (predisposed) to bipedal walking thanks to the skills of climbing trees. The body is oriented vertically, and the legs make movements reminiscent of those made when walking. However, anthropologist Robin Crompton of the University of Liverpool and his colleagues Suzanne Thorpe and Roger Holder of the University of Birmingham believe that it is difficult to infer a bipedal gait from vertical tree climbing, as well as from the gait of chimpanzees and gorillas. There are significant differences in the mechanics of these movements. For example, the knees of chimpanzees and gorillas almost never fully extend. As we already know, these monkeys sometimes move on the ground on two legs, but their legs remain bent. Their gait differs from humans in a number of other ways. Orangutans, the most “arboreal” of the large apes, are a different matter. [referring to the natural group including orangutans, gorillas, chimpanzees and hominids. In English this group is called great apes], whose behavior Crompton and his colleagues observed for a year in the forests of the island of Sumatra.

Anthropologists have recorded 2,811 single “acts” of orangutan movement in treetops. For each case, the number of supports (branches) used, their thickness, and method of movement were recorded. Orangutans have three such methods: on two legs (holding onto something with their hand), on all fours, clasping a branch with their fingers and toes, and on one hand, in a suspended state, from time to time grabbing something with their feet.

Statistical analysis of the collected data showed that the method of movement depends on the number and thickness of supports. On single thick, strong branches, orangutans usually move on all fours; on branches of medium diameter - on their arms. They prefer to walk carefully on thin branches with their feet, holding onto some additional support with their hands. At the same time, the gait of monkeys is very similar to that of humans - in particular, the legs are fully extended at the knees. It is this method of movement that seems to be the safest and most effective when it comes to moving along thin, flexible and precarious branches. An additional advantage is that one of the hands remains free for picking fruit.

The ability to walk on thin branches is not a small thing for tree monkeys. Thanks to this ability, they can move freely through the forest canopy and move from tree to tree without descending to the ground. This significantly saves energy, that is, reduces energy costs for obtaining food. Therefore, such an ability must be maintained by natural selection.

Orangutans separated from the common evolutionary trunk before gorillas, and gorillas before this trunk split into the ancestors of chimpanzees and humans. Researchers suggest that bipedal walking on thin branches was originally inherent in the distant ancestors of all large apes. Orangutans living in the tropical rainforests of Southeast Asia retained this skill and developed it; gorillas and chimpanzees lost it, instead developing their characteristic quadrupedal walking on the knuckles and the rarely used bipedal gait “half-bent.” This could be facilitated by the periodic “drying out” of tropical forests in Africa and the spread of savannas. Representatives of the human evolutionary line have learned to walk on the ground in the same way as on thin branches, straightening their knees.

According to Crompton and his colleagues, their assumption explains two groups of facts that seem quite mysterious from the point of view of other hypotheses of the origin of bipedality. Firstly, it becomes clear why forms close to the common ancestor of humans and chimpanzees (such as Sahelanthropus, Orrorin and Ardipithecus) already show clear signs of bipedality in their skeletal structure, and this despite the fact that these creatures did not live in the savannah , and in the forest. Secondly, the structure of the arms and legs of Australopithecus afarensis, the most well studied of the early representatives of the human line, no longer seems contradictory. U Australopithecus afarensis the legs are well adapted for bipedal walking, but the arms are very long, tenacious, more suitable for living in trees and grasping branches (see below).

According to the authors, humans and orangutans retained the ancient bipedal gait of their distant ancestors, but gorillas and chimpanzees lost it and instead developed something new - walking on their knuckles. It turns out that in this respect, humans and orangutans should be considered “primitive”, and chimpanzees and gorillas – “evolutionarily advanced” ( Thorpe et al., 2007).

The magnificent Ardi, the oldest well-studied (to date) hominid, brings even more clarity to the question of the origin of bipedalism.

In October 2009, a special issue of the journal Science was published, devoted to the results of a comprehensive study of the bones of Ardipithecus, a bipedal monkey that lived in northeastern Ethiopia 4.4 million years ago. View Ardipithecus ramidus was described in 1994 from several teeth and jaw fragments. In subsequent years, the collection of bone remains of Ardipithecus was significantly expanded and now includes 109 specimens. The biggest success was the discovery of a significant part of the skeleton of a female individual, which scientists solemnly presented to journalists and the general public under the name Ardi. In official documents, Ardi is listed as the skeleton of ARA-VP-6/500.

Eleven articles published in the special issue of Science summed up the results of many years of work by a large international research team. The publication of these articles and their protagonist, Ardi, were widely publicized, but this is by no means empty hype, because the study of Ardipithecus bones did allow for a more detailed and accurate reconstruction of the early stages of hominid evolution.

The assumption made earlier on the basis of the first fragmentary finds was confirmed that A. ramidus– an excellent candidate for the role of transitional link [a candidate, and not just a transitional link, because it cannot be strictly proven from fossil bones that someone was someone else's ancestor or descendant. However, in many cases this can be judged with a high degree of certainty, as in the case of Ardi] between the common ancestor of humans and chimpanzees (Orrorin and Sahelanthropus were apparently close to this ancestor) and later hominids - Australopithecus, from which, in turn, the first representatives of the human genus descended ( Homo).

Until 2009, the oldest hominid studied in detail was Lucy, an Australopithecus afarensis, who lived about 3.2 million years ago ( Johanson, Go, 1984). All more ancient species (in order of increasing antiquity: Australopithecus anamensis, Ardipithecus ramidus, Ardipithecus kadabba, Orrorin tugenensis, Sahelanthropus chadensis) were studied on the basis of fragmentary material. Accordingly, our knowledge about their structure, lifestyle and evolution also remained fragmentary and inaccurate. And now the honorary title of the most ancient of the well-studied hominids has solemnly passed from Lucy to Ardi.

DATING AND FEATURES OF THE BURIAL. Bones A. ramidus come from a single layer of sediment about 3 m thick, sandwiched between two volcanic layers. The age of these layers was determined using the argon-argon method [one of the most reliable methods for radiometric dating of volcanic rocks. It is the result of an improvement of the potassium-argon method, based on the constancy of the rate of transformation of the radioactive isotope 40 K into 40 Ar] and turned out to be the same (within the measurement error) - 4.4 million years. This means that the bone-bearing layer was formed (as a result of floods) relatively quickly - in a maximum of 100,000 years, but most likely in several millennia or even centuries.

Excavations began in 1981. In total, more than 140,000 samples of vertebrate bones were obtained, of which 6000 can be identified to families. Among them are 109 samples A. ramidus, belonging to at least 36 individuals. Fragments of Ardi's skeleton were scattered over an area of ​​about 3 m2. The bones were unusually fragile, so extracting them from the rock took a lot of work. Ardi's cause of death has not been established. She was not eaten by predators, but her remains, apparently, were thoroughly trampled by large herbivores. The skull was especially damaged, it was crushed into many fragments.

ENVIRONMENT. Along with the bones A. ramidus Remains of various animals and plants were found. Forest plants predominate among plants, and animals that feed on leaves or fruits of trees (rather than grass) predominate. Judging by these finds, Ardipithecus did not live in the savannah, but in wooded areas, where areas of dense forest alternated with more sparse ones. The ratio of carbon isotopes 12 C and 13 C in the tooth enamel of five individuals A. ramidus indicates that Ardipithecus fed mainly on forest products rather than savannah (savannah grasses are characterized by an increased content of the 13 C isotope). This is how Ardipithecus differs from its descendants - Australopithecus, which received from 30 to 80% of carbon from open space ecosystems (Ardipithecus - from 10 to 25%). However, Ardipithecus was still not purely forest dwellers, like chimpanzees, whose food is almost 100% of forest origin.

The fact that Ardipithecus lived in the forest seems at first glance to contradict the old hypothesis, according to which the early stages of hominid evolution and the development of bipedal walking were associated with the exit from the forest to the savannah. Similar conclusions had previously been drawn from studies of Orrorin and Sahelanthropus, which also apparently walked on two legs but lived in wooded areas. However, this situation can be looked at from another point of view if we remember that the forests in which early hominids lived were not very dense, and their bipedal walking was not very perfect. According to S.V. Drobyshevsky, the combination of a “transitional environment” with a “transitional gait” does not refute, but, on the contrary, brilliantly confirms the old views. Hominids moved from dense forests to open spaces gradually, and their gait just as gradually improved.

SKULL AND TEETH. Ardi's skull is similar to that of Sahelanthropus. Both species are characterized by a small brain volume (300–350 cm 3), a foramen magnum displaced forward (that is, the spine was attached to the skull not from behind, but from below, which indicates bipedal walking), and also less developed than in chimpanzees and gorilla , molars and premolars. Apparently, pronounced prognathism (protrusion of the jaws forward) in modern African apes is not a primitive trait and developed in them after their ancestors separated from the ancestors of humans.

Ardipithecus teeth are the teeth of an omnivore. The entire set of features (size of teeth, their shape, enamel thickness, the nature of microscopic scratches on the tooth surface, isotopic composition) indicates that Ardipithecus did not specialize on any one diet - for example, on fruits, like chimpanzees. Apparently, Ardipithecus fed both in trees and on the ground, and their food was not too tough.

One of the most important facts is that in males A. ramidus, unlike modern apes (except humans), the fangs were no larger than those of females. Male monkeys actively use their fangs both to intimidate rivals and as a weapon. The most ancient hominids ( Ardipithecus kadabba, Orrorin, Sahelanthropus) the fangs of males may also have been no larger than those of females, although there is not yet enough data for final conclusions. Obviously, in the human evolutionary line, sexual dimorphism (intersexual differences) in canine size disappeared very early. We can say that the males have had a “feminization” of their fangs. In chimpanzees and gorillas, dimorphism apparently increased a second time; males acquired very large fangs. Male bonobos have smaller fangs than other living apes. Bonobos are also characterized by the lowest level of intraspecific aggression. Many anthropologists believe that there is a direct connection between the size of male canines and intraspecific aggression. In other words, it can be assumed that the reduction of canines in our distant ancestors was associated with certain changes in the social structure. For example, with a decrease in conflicts between males.

BODY SIZE. Ardi's height was approximately 120 cm, weight - about 50 kg. Males and females of Ardipithecus were almost the same in size. Weak sexual dimorphism in body size is also characteristic of modern chimpanzees and bonobos, with their relatively equal relationships between the sexes. In gorillas, on the contrary, dimorphism is very pronounced, which is usually associated with polygamy and the harem system. In the descendants of the Ardipithecus, the Australopithecus, sexual dimorphism may have increased (see below), although this was not necessarily associated with male dominance over females and the establishment of a harem system. The authors admit that males may have grown larger and females may have shrunk due to their move out into the savannah, where males had to take upon themselves to protect the group from predators, and females may have learned to cooperate better with each other, which made physical power less important to them .

POSTCRANIAL SKELETON. Ardie walked on the ground on two legs, although less confidently than Lucy and her relatives, the Australopithecus. At the same time, Ardi has retained many specific adaptations for effective tree climbing. In accordance with this, in the structure of Ardi's pelvis and legs there is a combination of primitive (climbing-oriented) and advanced (walking-oriented) features.

Ardi's hands are exceptionally well preserved (unlike Lucy's hands). Their study allowed us to draw important evolutionary conclusions. As we already know, it was long believed that human ancestors, like chimpanzees and gorillas, walked by leaning on their knuckles. This peculiar method of movement is characteristic only of African apes and orangutans; other monkeys usually rest on their palm when walking. However, Ardi's hands are devoid of specific features associated with "knuckle walking". The hand of Ardipithecus is more flexible and mobile than that of chimpanzees and gorillas, and in a number of ways is similar to humans. It is now clear that these characteristics are primitive, original to hominids (and possibly to the common ancestor of humans and chimpanzees). The structure of the hand, characteristic of chimpanzees and gorillas (which, by the way, does not allow them to manipulate objects as deftly as we do), on the contrary, is advanced and specialized. The strong, prehensile hands of chimpanzees and gorillas allow these massive animals to move efficiently through trees, but are poorly suited for fine manipulation. The hands of Ardipithecus allowed him to walk along the branches, leaning on his palms, and were better suited for tool work. Therefore, in the course of further evolution, our ancestors did not have to “remake” their hands that much.

In the structure of the foot of Ardipithecus there is a mosaic of signs indicating the preservation of the ability to grasp branches (opposite big toe) and at the same time effective bipedal walking (a more rigid arch than that of modern apes). The descendants of Ardipithecus - Australopithecus - lost the ability to grab branches with their feet and acquired an almost completely human foot structure.

Ardipithecus presented anthropologists with many surprises. According to the authors, no one could have predicted such a mixture of primitive and advanced features, which was found in Ardipithecus, without having real paleoanthropological material in hand. For example, it never occurred to anyone that our ancestors first adapted to walk on two legs due to transformations in the pelvis and only later abandoned the opposable thumb and the grasping function of the feet.

Thus, the study of Ardipithecus showed that some popular hypotheses about the paths of hominid evolution need to be revised. Many features of modern apes turned out to be not primitive at all, but advanced, specific features of chimpanzees and gorillas, associated with deep specialization for climbing trees, hanging on branches, “knuckle walking,” and a specific diet. Our common ancestors did not have these characteristics. Those monkeys from which man descended were not very similar to those of today.

Most likely, this concerns not only the physical structure, but also behavior and social structure. Perhaps chimpanzee thinking and social relationships are not such a good model for reconstructing the thinking and social relationships of our ancestors. In the final article of the special issue of Science, the famous American anthropologist Owen Lovejoy calls for abandoning the usual ideas according to which australopithecines were something like chimpanzees that learned to walk upright. Lovejoy emphasizes that in reality, chimpanzees and gorillas are extremely unique, specialized, relict primates, hidden in impenetrable tropical forests and only because of this have survived to this day. Based on new evidence, Lovejoy developed a very interesting model of early hominid evolution, which will be discussed in the next section.

Family relationships are the key to understanding our evolution

Most hypotheses about the paths and mechanisms of anthropogenesis traditionally revolve around two unique features of humans: a large brain and complex tool activity. Owen Lovejoy is among those anthropologists who believe that the key to understanding our origins is not enlarged brains or stone tools (these traits appeared very late in hominid evolution), but other unique features of the “human” evolutionary line related to sexual behavior , family relationships and social organization. Lovejoy defended this point of view back in the early 1980s. At the same time, he suggested that the key event in the early evolution of hominids was the transition to monogamy, that is, to the formation of stable mating pairs ( Lovejoy, 1981). This assumption was then repeatedly challenged, revised, confirmed and denied ( Butovskaya, 2004) [the largest Russian anthropologist M.L. Butovskaya believes that our distant ancestors most likely practiced so-called serial monogamy. This type of relationship is typical for modern European civilization: they got married, lived together for several years (on average, about as long as it takes to raise a child), then divorced and changed partners. Similar customs are found among modern hunter-gatherers such as the Hadza of Tanzania].

New evidence from Ardipithecus strengthens the case for the central role of changes in social and sexual behavior in early hominid evolution. The study of Ardipithecus showed that chimpanzees and gorilla are not the best reference points for reconstructing the thinking and behavior of our ancestors. As long as Lucy remained the oldest well-studied hominid, it was still possible to assume that the last common ancestor of humans and chimpanzees was broadly similar to chimpanzees. Ardi radically changed this situation. It became clear that many of the characteristics of chimpanzees and gorillas are relatively recently acquired specific features of these relict primates. Human ancestors did not have these characteristics. If what has been said is true for feet, hands and teeth, then it may well be true for behavior and family relationships. Therefore, we should not assume that the social life of our ancestors was much the same as that of modern chimpanzees. Chimpanzees aside, we can focus on the information that fossil material provides.

Lovejoy attaches great importance to the fact that Ardipithecus males, as already mentioned, did not have large fangs, which could, like other monkeys, be constantly sharpened by the molars of the lower jaw and used as a weapon and a means of intimidating male competitors. The reduction of canine teeth in later hominids—australopithecines and humans—has previously been interpreted as either a byproduct of the enlargement of molars (molars) or as a consequence of the development of the lithic industry, which made these natural weapons redundant. It has long been clear that tusks decreased long before the production of stone tools began (about 2.6 million years ago). A study of Ardipithecus showed that the reduction of fangs also occurred long before the molars of Australopithecus increased (which was possibly associated with the exit to the savannah and the inclusion of tough rhizomes in the diet). Therefore, the hypothesis about the social reasons for the reduction of canines began to look more convincing. Large canines in male primates are a reliable indicator of intraspecific aggression. Therefore, their decrease in early hominids most likely indicates that relationships between males became more tolerant. They began to quarrel less with each other over females, territory, and dominance in the group.

Apes in general are characterized by the so-called K-strategy . Their reproductive success depends less on fertility than on the survival of the young. Apes have a long childhood, and females spend a huge amount of time and effort to raise each baby. While the female is nursing the cub, she is not capable of conceiving. As a result, males are constantly faced with the problem of a lack of “qualified” females. Chimpanzees and gorillas solve this problem by force. Male chimpanzees unite in fighting groups and carry out raids on the territories of neighboring groups, trying to expand their domain and gain access to new females. Male gorillas expel potential competitors from the family and strive to become the sole owners of the harem. For both of them, large fangs are not a luxury, but a means to leave more offspring. Why did early hominids abandon them?

Another important component of the reproductive strategy of many primates is the so-called sperm wars. They are characteristic of species that practice free sexual relations in groups that include many males and females. Large testes are a reliable indicator of sperm wars. Gorillas, with their tightly guarded harems, and solitary orangutans (also inveterate polygamists, although their mates usually live separately rather than in a single group) have relatively small testes, just like people. Sexually liberated chimpanzees have huge testes. Important indicators are also the rate of sperm production, the concentration of sperm in it and the presence of special proteins in the seminal fluid that create obstacles for foreign sperm. Based on the totality of all these signs, we can conclude that in the evolutionary history of man there were regular sperm wars at one time, but have long since ceased to play a significant role.

If the males of early hominids did not fight each other over females and did not get involved in sperm wars, then they found some other way to ensure their reproductive success. This method is known, but it is quite exotic - only about 5% of mammals practice it. This is monogamy - the formation of strong married couples. Males of monogamous species tend to take an active part in caring for the offspring.

Lovejoy believes that monogamy may have evolved from a behavior found in some primates, including (albeit infrequently) chimpanzees. We are talking about “mutually beneficial cooperation” between the sexes based on the principle of “sex in exchange for food.” This behavior may have developed particularly strongly in early hominids due to their diet. Ardipithecus were omnivores, foraging both in trees and on the ground, and their diet was much more varied than that of chimpanzees and gorillas. It must be borne in mind that among monkeys omnivory is not synonymous with indiscriminate eating - on the contrary, it presupposes high selectivity, gradation of food preferences, and an increase in the attractiveness of certain rare and valuable food resources. Gorillas, who eat leaves and fruits, can afford to wander lazily through the forest, moving only a few hundred meters a day. Omnivorous Ardipithecus had to act more energetically and travel much longer distances to get something tasty. At the same time, the danger of falling into the teeth of a predator increased. It was especially difficult for females with cubs. Under such conditions, the strategy of “sex in exchange for food” became very advantageous for females. Males who nursed females also increased their reproductive success because their offspring had a better chance of survival.

Chimpanzees steal fruit from other people's gardens to entice females.

An international team of zoologists from the US, UK, Portugal and Japan spent two years observing a family of wild chimpanzees in the forests around the village of Bossou in Guinea, near the border with Ivory Coast and Liberia. These observations provided insight into relationships among wild chimpanzees , not spoiled by intrusive human attention and training.

The family's territory occupied an area of ​​approximately 15 km2 and was closely adjacent to human habitation. The people's economy also included fruit tree plantations. The chimpanzee family at different times consisted of from 12 to 22 individuals, of which only three were always males. These males constantly raided fruit plantations. On average, each male climbed into someone else's garden 22 times a month. The males understood the danger of the illegal enterprise, showing their anxiety by characteristic scratching. Going on business, the male kept looking around to see if there was anyone watching, then quickly climbed a tree, instantly plucked two fruits - one in his teeth, the other in his hand - and quickly, quickly left the dangerous territory.

Thieving raids by chimpanzees look just like boyish forays into a neighboring orchard for apples. And the purpose of these raids, as it turned out, is not too different from the boy’s thoughts: to show off the booty to his comrades and appear as heroes to the girls. Chimpanzees do not bring stolen fruits to their family in order to quietly devour them in a corner. Males treat females with them!

It must be remembered that chimpanzees, like other apes, rarely share food with each other (except, of course, for mothers and babies). And this treat is not free. Males offer it to females who are ready to mate. The females behave correctly and do not ask for a treat; the male himself chooses whom to treat. As we see, the strategy of “sex in exchange for food” in promiscuous groups of chimpanzees can also work, although not as effectively as with monogamy.

In this family, one of the females was clearly superior to the others in attractiveness. In 83% of cases, males treated her with fruit. After this, the female, accepting courtship, moved away with the chosen one to the borders of the territory. At the same time, she clearly preferred the courtship of one of the applicants, and this was not a dominant alpha male at all, but a subordinate beta male: with him she spent more than half of her time. The dominant male was less likely than others to share ill-gotten fruits with her: only in 14% of cases did he invite her to treat himself.

Observers also note the following fact: the males preferred this particular female, despite the fact that there was another in the family, physiologically more prepared for reproduction. An uninvited thought immediately comes to mind that male chimpanzees assessed their female friends not only by their readiness to reproduce, but also by other subjective criteria, but, naturally, the authors of the publication refrained from such speculation. These remarkable observations nevertheless led them to the well-founded conclusion that for chimpanzees, stealing is not a way to get food. After all, they do not share “real” forest food. This is a way to maintain your authority, as is typical of a dominant male, or to win the sympathy of females ( Hockings et al., 2007).

If the males of ancient hominids made it a rule to carry food to females, then over time special adaptations should have developed to facilitate this behavior [in such intelligent animals as monkeys, behavior may first change, and the changes will be preserved through a series of generations through imitation and learning, as a cultural tradition. This leads to a change in the direction of selection, because mutations that make life easier for this particular behavior will now be maintained and spread. As a result, this can lead to the consolidation of new psychological, physiological and morphological characteristics. This way of forming evolutionary innovations is called the Baldwin effect. We'll talk more about it in future chapters]. The obtained tidbits had to be transported over considerable distances. It's not easy if you walk on all fours. Lovejoy believes that bipedality, the most striking characteristic of hominids, evolved precisely in connection with the custom of providing food for females. An additional incentive could have been the use of primitive tools (for example, sticks) to pick out hard-to-reach food objects.

The changed behavior should have affected the nature of social relations in the group. The female was interested, first of all, in ensuring that the male did not abandon her, and the male - that the female did not cheat on him. The achievement of both goals was desperately hampered by the way female primates "advertise" ovulation, or the time when a female is fertile. Such advertising is beneficial if society is organized like that of a chimpanzee. But in a society with a predominance of stable pair bonds, developed on the basis of the “sex in exchange for food” strategy, the female is absolutely not interested in arranging long periods of abstinence for her male (she will stop feeding or even leave for someone else, scoundrel!). Moreover, it is beneficial for the female that the male cannot determine at all whether conception is possible at the moment. Many mammals detect this by smell, but in hominids, selection has favored the reduction of many olfactory receptors. Males with a deteriorated sense of smell fed their families better—and became more desirable mating partners.

The male, for his part, is also not interested in his female advertising her readiness to conceive and creating unnecessary excitement among other males - especially if he himself is currently “on the hunt.” Females who concealed ovulation became preferred partners because they had fewer reasons for adultery.

As a result, female hominids lost all external signs of readiness (or unreadiness) for conception; including, it became impossible to determine by the size of the mammary glands whether the female now has a baby. In chimpanzees, as in other primates (except humans), the size of the mammary glands indicates whether the female is fertile. Enlarged breasts are a sign that the female is now nursing a baby and cannot conceive a new one. Male chimpanzees rarely mate with lactating females and are not attracted to enlarged breasts.

Humans are the only primates in which females have permanently enlarged breasts (and some males like it). But why did this trait initially develop - to attract males or, perhaps, to discourage them? Lovejoy considers the second option more plausible. He believes that permanently enlarged breasts, which did not provide any information about the female's ability to conceive, were part of a set of measures to strengthen monogamy and reduce hostility between males.

As pair bonds strengthened, female preferences would gradually shift from the most aggressive and dominant males to the most nurturing. In animal species in which males do not care for the family, choosing the “coolest” (dominant, masculine) male is often the best strategy for the female. Paternal care for offspring radically changes the situation. Now it is much more important for the female (and her offspring) that the male be a reliable provider. External signs of masculinity (masculinity) and aggressiveness, such as large fangs, begin to repel females rather than attract them. A male with large canines is more likely to increase his reproductive success through forceful means, through fights with other males. Such husbands go out of fashion when a diligent and reliable breadwinner husband is needed for the survival of the offspring. Females who choose fighter husbands raise fewer cubs than those who choose non-aggressive hard workers. As a result, females begin to prefer males with small fangs - and under the influence of sexual selection, the fangs quickly decrease.

Sad ladies choose not the most courageous gentlemen

Few biologists would deny that adaptations associated with the choice of a marriage partner play a huge role in evolution (see the chapter “The Origin of Man and Sexual Selection”). However, there are still many blank spots in our knowledge about these adaptations. In addition to purely technical difficulties, their study is hampered by stereotypes. For example, researchers often overlook the seemingly obvious possibility that the mating preferences of different individuals of the same species do not necessarily have to be the same. It seems natural to us to think that if, for example, the average peacock prefers males with large and bright tails, then this must certainly be true for all peacocks at all times. But this is not necessarily the case. In particular, the so-called choice with an eye on oneself is possible - when an individual prefers partners who are somewhat similar or, conversely, not similar to itself. Moreover, even for the same individual, preferences can change depending on the situation - for example, on the degree of stress or on the phase of the estrous cycle.

A successful choice of a sexual partner is a matter of life and death for your genes, which in the next generation will mix with the genes of your chosen one. This means that any hereditary changes that even slightly affect the optimal choice will be extremely intensively supported or, conversely, rejected by natural selection. Therefore, we have the right to expect that partner selection algorithms that have developed during evolution in different organisms can be very sophisticated and flexible. These arguments are quite applicable to people. Research in this area can help find a scientific approach to understanding the most subtle nuances of human relationships and feelings. However, few such studies have been conducted so far.

Recently, two seemingly completely unrelated articles were published in the journals Evolutionary Psychology and BMC Evolutionary Biology. One study was performed on humans, the other on house sparrows, but the patterns identified in them are similar. It makes you think, to say the least.

Let's start with sparrows. These birds are monogamous, that is, they form stable pairs, and both parents take care of the offspring, but adultery is common. In short, family relationships among sparrows differ little from those found in most human populations. In male house sparrows, the main sign of masculinity is a black spot on the chest.

It has been shown that the size of the spot is an “honest” indicator of the health and strength of the male (which depends on the quality of the genes) and is directly related to his social status. Males with a large spot occupy the best areas, more successfully defend their female from the attacks of other males, and produce, on average, more offspring than males with a small spot. It has also been shown that the reproductive success of females who have linked their lives with the owner of a large spot is, in most populations, on average higher than that of “losers” who got a less bright male as their husband.

From these facts, it would seem to follow that it should always and under any circumstances be beneficial for sparrows to give preference to males with a large spot. Austrian scientists from the Institute of Ethology named after. Konrad Lorenz in Vienna. They suggested that females' preferences might depend on their own condition. In particular, it was expected that females in poor physical condition might be less choosy. Reduced selectivity in unattractive individuals has previously been noted in several animal species.

The ratio of body weight to the cubed length of the metatarsus was used as a measure of the female's physical condition. This indicator simply reflects the fatness of the bird, which, in turn, depends on its health and the conditions in which it grew up. It is known that this value in passerines is positively correlated with indicators of female reproductive success, such as clutch size and the number of surviving chicks.

The experiment involved 96 sparrows and 85 sparrows caught at the Vienna Zoo. The initial size (length) of the black spot in all males selected for the experiment was less than 35 mm. For half of the males, the spot was drawn on with a black marker to 35 mm, which approximately corresponds to the average size of the spot in males of this species, and for the other half - to 50 mm, which corresponds to the maximum size. Female preferences were determined using a standard method commonly used in similar studies. Two males with different spot sizes were placed in the two outer enclosures, and a female was placed in the central enclosure and they looked at which of the males the female would spend more time next to.

It turned out that there is a strict negative correlation between the female’s fatness and the time she spends next to the “worse” of the two males. In other words, the worse the female’s condition, the less time she spends next to the owner of a large spot and the stronger her attraction to a male with a medium-sized spot. At the same time, contrary to theoretical expectations, well-fed females did not demonstrate clear selectivity. They spent, on average, approximately the same amount of time near each of the two males. Stunted females, on the contrary, showed strict selectivity: they strongly preferred “average” males and avoided those with a huge spot.

This appears to be one of the first ethological studies to demonstrate a preference for inferior males by inferior females. A similar result was obtained on zebra finches, and this work was also published quite recently ( Holveck, Riebel, 2010). Previously, something similar was noticed in stickleback fish ( Bakkeret et al., 1999). Unlike Vienna sparrows, female finches and sticklebacks that are in good shape clearly prefer “high quality” males.

The authors suggest that the strange preferences of skinny sparrows may be explained by the fact that males with a small spot are more caring fathers. Some facts and observations indicate that weak males with a small spot try to compensate for their shortcomings by taking on more parental troubles. A strong sparrow, in principle, can raise chicks without the help of a spouse, so she can afford to take a healthy and strong male with a large spot as her husband, even if he is a bad father, in the hope that the offspring will inherit his health and strength. A weak female cannot cope alone, so it is more profitable for her to choose a less “prestigious” spouse if there is a hope that he will spend more energy on the family. Isn't it true that this is somewhat reminiscent of the situation that developed, according to Lovejoy, among Ardipithecus?

Previous research has shown that female preferences may vary among sparrow populations. In some populations, females, on average, as expected according to theory, prefer males with the largest spots. In others this is not observed (as in the Vienna Zoo population). According to the authors, this variability is partly explained by the fact that different populations may have different numbers of females in good and bad physical shape ( Griggio, Hoi, 2010).

A similar study, but not on sparrows, but on humans, was carried out by psychologists from Oklahoma State University. They examined the influence of thoughts about death on how women rate the attractiveness of male faces that vary in degree of masculinity (masculinity).

If we talk about “average” preferences, then women, as a rule, prefer more masculine faces if they themselves are in that phase of the menstrual cycle when the likelihood of conception is high. When the likelihood of conception is low, women usually prefer men with more feminine (feminine) faces.

Psychologists' interest in the effects of death reminders stems from the fact that, as numerous observations and experiments have shown, such reminders have a profound impact on people's reproductive behavior. One manifestation of this influence is the surge in birth rates, often observed after major disasters or natural disasters. Reminders of the inevitability of death heighten people's interest in the reproductive sphere and stimulate the desire to have children. For example, if subjects are reminded before testing that they are mortal, the percentage of positive responses to questions like “Would you like to have another child?” increases noticeably. There have been quite a few such studies, and they all gave similar results. In China, after being reminded of death, subjects became less inclined to support birth control policies; in America and Israel, such reminders increased the willingness of young ladies to enter into “risky” sexual relationships with the risk of becoming pregnant.

Psychologists from the University of Oklahoma decided to test whether reminders of death influence women's preferences when evaluating male faces. The study involved 139 female students not taking hormonal medications. The subjects were randomly divided into two groups – experimental and control. Before testing, students from the first group were asked to write a short essay on the topic “My feelings about my own death and what will happen to me when I die.” For the control group, the essay topic “death” was replaced with “upcoming exam.” Then, in accordance with accepted methods, the students completed a short “distracting” task so that some time passed between the reminder of death and testing. After this, the subjects were presented with computer-generated sequences of faces - from extremely masculine to extremely feminine. It was necessary to choose the “most attractive” one from these faces.

It turned out that reminders of death greatly influence women's preferences. Students in the control group, as in all previous studies of this kind, preferred more masculine faces if they themselves were ready to conceive, and less masculine if they were in a phase of the cycle when conception was unlikely. But among the students who had to write an essay about their own death, their tastes changed dramatically: they liked less masculine faces in the fertile phase and more masculine ones in the infertile phase.

The authors discuss several possible interpretations of the results obtained (it is clear that many can be invented). One of the proposed explanations seems the most interesting in the light of the data on sparrows and ardipithecines described above. Perhaps the reminder of death induces women to choose not “good genes” for their potential children, but a “caring father.” The fact is that in men, like sparrows, there is a negative correlation between the severity of masculine characteristics and the tendency to take care of his wife and children. In addition, men with the most masculine faces are, on average, less likely to engage in prosocial behavior and adherence to social norms. They are more aggressive, and therefore life with them involves a certain risk. Probably, thoughts about the inevitability of death can affect women in much the same way as sparrows - awareness of their own weakness. Both encourage females to rely not on “good genes”, but on a potentially more caring father ( Vaughn et al. 2010). Maybe Ardi’s sisters, burdened with children, omnivorous, always hungry, felt the same?

Lovejoy's model is the "adaptive complex" of early hominids. Arrows between rectangles indicate cause-and-effect relationships, arrows inside rectangles indicate an increase or decrease in the corresponding indicators. In the last common ancestor of humans and chimpanzees, groups likely consisted of many males and females interbreeding relatively freely. They had moderate polymorphism in canine size and low levels of aggression between males; Sperm wars took place. Early hominids evolved three unique traits (dark triangles), two of which are documented in the fossil record (bipedalism and reduced canine teeth). Suggested cause-and-effect relationships: 1) the need to carry food led to the development of bipedality; 2) the choice of non-aggressive partners by females leads to a reduction in fangs; 3) the need to protect against “marital infidelity” (in both sexes) leads to the development of hidden ovulation. This course of evolution is generated by two groups of factors: the food strategy of early hominids (left column) and the “demographic dilemma” caused by the intensification of the K-strategy (right column). The selection pressure caused by these factors leads to the development of the sex-for-food strategy. The subsequent increase in male growth and effective cooperation between males in Australopithecus afarensis ensured the effectiveness of collective foraging raids. This made it possible to further develop the production of carrion in the savannah, and then collective hunting (genus Homo). This “economic revolution” contributed to the improvement of adaptations to bipedal walking, further strengthening of intra-group cooperation and reduction of intra-group aggression, an increase in the amount of energy that could be allocated to raising offspring, an increase in the birth rate and survival of children. It also loosened restrictions on the development of high-value tissue (the brain). Based on a drawing from Lovejoy, 2009.

As a result of the events described, our ancestors formed a society with a reduced level of intra-group aggression. Perhaps intergroup aggression also decreased, because with the lifestyle that Ardipithecus supposedly led, it is difficult to assume developed territorial behavior. The uneven distribution of resources across the territory, the need to travel long distances in search of valuable food items, the high risk of being eaten by a predator - all this made it difficult (although it did not completely exclude) the existence of clear boundaries between groups and their protection.

The reduction in intragroup aggression created the preconditions for the development of cooperation and mutual assistance. Reduced antagonism between females allowed them to cooperate to care for their young. Reduced antagonism between males made it easier to organize joint raids to obtain food. Chimpanzees also occasionally practice collective hunting, as well as collective fighting against neighboring groups of chimpanzees. In early hominids this behavior was probably much more developed.

This opened up new ecological opportunities for hominids. Valuable food resources, which were impossible or extremely dangerous to obtain alone (or in small, poorly organized groups, ready to scatter at any moment), suddenly became available when male hominids learned to unite into close-knit groups, where everyone could rely on a comrade.

From this it is not difficult to deduce the subsequent development by the descendants of Ardipithecus of completely new types of resources - including the transition to feeding on carrion in the savannah (this was undoubtedly a very risky business, requiring a high level of cooperation between males; see below), and then to collective hunting for large animals. game.

The subsequent enlargement of the brain and the development of the lithic industry in Lovejoy's model appears as a secondary - and even to a certain extent accidental - consequence of the direction of specialization that early hominids took. The ancestors of chimpanzees and gorillas had the same initial capabilities, but they were “led” along a different evolutionary route: they relied on a forceful solution to matrimonial problems, and therefore the level of intra-group antagonism remained high and the level of cooperation low. Complex tasks, the solution of which requires coordinated actions of close-knit and friendly teams, remained inaccessible to them, and as a result, these monkeys never became intelligent. Hominids "chose" an unconventional solution - monogamy, a rather rare strategy among mammals, and this ultimately led them to the development of intelligence.

Lovejoy's model ties together three unique features of hominids: bipedalism, small canines, and hidden ovulation. Its main advantage lies precisely in the fact that it gives a unified explanation for these three features, and does not look for separate reasons for each of them.

Lovejoy's model has been around for 30 years. All its components have long been the subject of lively discussion in the scientific literature. Lovejoy relies on a variety of facts and theoretical developments, and not just on the meager information and simple reasoning that can be presented in a popular book. New data on Ardipithecus fit extremely well into Lovejoy’s theory and made it possible to clarify its details. Lovejoy is well aware that his model is speculative and some aspects of it will not be easy to confirm or refute ( Lovejoy, 2009). Nevertheless, this is, in my opinion, a good theory, consistent with most known facts. One can hope that subsequent anthropological discoveries will gradually make some of its provisions generally accepted.

Back to the childhood?

We said above that the reduction of canines in males of early hominids can be considered “feminization.” Indeed, the reduction of one of the characteristic “male” ape characteristics made male hominids more similar to females. This may have been due to a decrease in the production of male sex hormones or a decrease in the sensitivity of certain tissues to these hormones.

See orangutans and gorillas at the zoo. In the Moscow Zoo, for example, there is now one gorilla and two orangutan families. They live in spacious enclosures, feel good there, and you can watch them for hours, which is what I sometimes do. It doesn't take a biologist to notice how much more human-like the females of these two species are than the males. A seasoned male orangutan or gorilla looks creepy, he is all covered with secondary sexual characteristics that demonstrate masculinity and strength: a humped silver back, a brutal look, incredible pancake-shaped cheeks, huge folds of black skin on his chest. There is little humanity in them. But their girls are quite cute. You probably won’t take someone like that as your wife, but just take a walk, sit in a cafe, chat about this and that...

In addition to feminization, there was another important trend in the evolution of our ancestors. In terms of the shape of the skull, the structure of the hair, the size of the jaws and teeth, a person is more similar to baby monkeys than to adults. Many of us retain curiosity and playfulness for a long time - traits that are characteristic of most mammals only in childhood, while adult animals are usually gloomy and incurious. Therefore, some anthropologists believe that neoteny, or juvenileization, a delay in the development of certain characteristics, leading to the preservation of childish traits in adult animals, played an important role in human evolution.

We can also talk about a broader concept – heterochrony. This is the name given to any changes in the rate and sequence of formation of various characters during development (neoteny is a special case of heterochrony). For example, according to one theory, the accelerated development of socially oriented mental abilities played an important role in human evolution (see chapter “The Social Brain,” book 2).

Juvenilization could also contribute to the transition to monogamy. After all, in order for married couples to become at least somewhat stable, the partners must experience special feelings for each other, and mutual affection must form between them. In evolution, new characteristics rarely arise out of nothing; usually some old character is used, which, under the influence of selection, undergoes a certain modification. The most suitable “preparation” (pre-adaptation) for the formation of stable marital attachment is the emotional connection between mother and child. The study of mono- and polygynous species of rodents gives reason to believe that the system of forming strong family ties has repeatedly developed during evolution precisely on the basis of the more ancient system of forming an emotional connection between a mother and her offspring (see chapter “Genetics of the Soul,” book 2).

Something similar may have happened in the relatively recent history of mankind, about 10–15 thousand years ago, when our ancestors began to domesticate wild animals.

In 2006, Emanuela Prato-Previde and her colleagues from the Milan Institute of Psychology conducted a series of observations of the behavior of dogs and their owners under unusual, stressful conditions. First, each couple (a dog and its owner) was placed in a half-empty room with a strange setting consisting of a couple of chairs, a cup of water, an empty plastic bottle, two balls, a toy on a string, a squeaky toy, and a video camera that recorded everything that was happening. Then the owner was taken to the next room, where he could watch on the monitor the suffering of the dog left alone. After a short separation the owner was allowed back. Then followed a second, longer separation and a new happy reunion.

The human participants in the experiment (among them there were 15 women and 10 men) were told by cunning psychologists that they were interested in the behavior of the dog and asked to behave as naturally as possible. In fact, the object of the study was not the dogs, but their owners. Every action of the test subjects was carefully recorded and classified. The exact number of strokes, hugs, kisses, play activities, and so on was counted. Particular attention was paid to the spoken words.

It turned out that both men and women, when communicating with their four-legged friend, used many behavioral elements characteristic of communication between parents and young children. Particularly revealing were the speeches of the subjects, which were replete with repetitions, diminutive forms of words, affectionate names and other characteristic features of the so-called mother language. After a long separation (accompanied by greater stress both for the “abandoned” dog and for the owner who observed its experiences), the play activity of the subjects decreased noticeably, but the number of hugs and other lisps increased. Men chatted slightly less with their dogs than women, but this could be due to the fact that men react more strongly to the presence of a video camera: perhaps they were afraid of appearing funny by talking to a dog. There were no other significant differences in the behavior of men and women.

In this purely observational-descriptive study, there were no controls, no large statistics, no artificial viruses were injected into anyone's brain, no genes were turned off, and no jellyfish was made to glow with green fluorescent protein. Nevertheless, the authors believe that their results are a serious argument in favor of the hypothesis that the dog-human symbiosis was initially built on the transfer of the parental behavior stereotype to new four-legged friends ( Prato-Previde et al., 2006). This hypothesis is confirmed by other facts. For example, in some traditional cultures, untouched by civilization, it is customary to keep a lot of completely useless pets, and in many cases they are treated exactly like children, women even breastfeed them ( Serpell, 1986). Perhaps the first wolf cubs that settled in the dwelling of Paleolithic man did not perform any utilitarian functions and our ancestors sheltered them not to help in the hunt, guard the cave or eat leftovers, but only for spiritual comfort, for friendship, for mutual understanding? A romantic hypothesis, but quite respected by many psychologists.

The ability to transfer to other social partners the style of behavior developed for communicating with children could play an important role in human evolution. It is possible that the juvenileization of the appearance and behavior of adult hominids was supported by selection, because their mating partners experienced more tender feelings towards such individuals, slightly similar to children. This could increase their reproductive success if wives were less likely to cheat on such husbands (who, most likely, were also less aggressive and more reliable), and husbands were less likely to leave their girl wives, whose whole appearance spoke of how needy they were. in protection and support. So far this is just fortune telling, but still some indirect arguments in favor of this guess can be given.

If juvenilization really took place in the evolution of human thinking and behavior, then something similar could well have happened in the evolution of our closest relatives - chimpanzees and bonobos. These two species differ markedly in their character, behavior and social structure. Chimpanzees are quite sullen, aggressive and warlike; in their groups, males usually dominate. Bonobos live in more abundant habitats than chimpanzees. Perhaps this is why they are more carefree and good-natured, make peace easier, their females are better able to cooperate and have more “political weight” in the team. In addition, the structure of the bonobo skull, like that of humans, shows signs of juvenileization. Perhaps similar signs can be found in the behavior of bonobos?

Recently, American anthropologists from Harvard University and Duke University decided to test whether chimpanzees and bonobos differ in the chronology of development of some features of thinking and behavior associated with social life ( Wobber et al., 2010). To do this, three series of experiments were carried out with chimpanzees and bonobos leading a semi-wild (or “semi-free”) lifestyle in special “shelters”, one of which is located on the northern coast of the Congo (chimpanzees live there), the other on the southern coast, in the bonobo patrimony . Most of these monkeys were confiscated from poachers at an early age, and only a few were born in the refuge.

In the first series of experiments, monkeys were allowed in pairs into a room where there was something tasty. The division into pairs was carried out so that each pair had monkeys of approximately the same age and that there were approximately equal numbers of same- and opposite-sex pairs. Three types of treats were used, differing in the ease of “monopolization” (some were easier to appropriate entirely, others were more difficult). The researchers monitored whether the monkeys would feast together or whether one of them would grab everything for himself. In addition, cases of gaming and sexual behavior were recorded.

It turned out that young chimpanzees and bonobos are equally willing to share food with their comrades. As they age, however, chimpanzees become more greedy, while bonobos do not. Thus, bonobos retain a “childish” trait into adulthood - the absence of greed.

Bonobos were more likely than chimpanzees to play games in this experiment, including sexual ones. In both species, playfulness declined with age, but in chimpanzees it happened more quickly than in bonobos. Thus, in this respect, bonobos also behave “childishly” when compared to chimpanzees.

In a second series of experiments, monkeys were tested on their ability to refrain from meaningless actions in a specific social context. Three people were placed shoulder to shoulder in front of the monkey. The two outermost people took treats from a container inaccessible to the monkey, while the middle one took nothing. Then all three extended their hand clenched into a fist to the monkey, so that it was not visible whose fist was empty and who had a treat. The monkey could ask for food from any of the three. It was considered that the monkey solved the problem correctly if it asked only from the two extreme ones, who took a treat from the container before its eyes, and did not ask from the middle one.

Chimpanzees, as it turned out, are already excellent at this task at the age of three and retain this skill throughout their lives. Small bonobos, on the other hand, often make mistakes and ask all three for food. Only by the age of 5-6 years do bonobos catch up with chimpanzees in the frequency of correct decisions. Thus, in this case, we can talk about a delay in the mental development of bonobos compared to chimpanzees. Of course, we are not talking about mental retardation. Bonobos are not dumber than chimpanzees, they are just more carefree and less severe in their social lives.

In the third series of experiments, the monkeys were given a more difficult task - to adapt to changes in human behavior. You had to ask for food from one of two experimenters. During preliminary tests, one of the two always gave the monkey a treat, while the other never did. The monkey, naturally, got used to this and began to choose the “kind” experimenter over and over again. Then the roles suddenly changed: the kind experimenter became greedy, and vice versa. Scientists monitored how quickly the monkey would understand what had happened and change its behavior in accordance with the changed situation. The results were approximately the same as in the previous series of experiments. Beginning at the age of five, chimpanzees quickly relearned and began to choose the experimenter who treated them now, and not in the past. Young bonobos coped with the task worse and caught up with chimpanzees only by the age of 10-12 years.

These results are in good agreement with the hypotheses about the important role of heterochronies in the evolution of thinking in great apes and that bonobos are characterized by delayed development (juvenilization) of some mental traits compared to chimpanzees. Perhaps the root cause of the differences found is the reduced level of intraspecific aggression in bonobos. This, in turn, may be due to the fact that bonobos live in more abundant areas and have less competition for food.

The authors point out that artificial selection for reduced aggressiveness during domestication in some mammals led to the juvenileization of a number of traits. In particular, they mention the famous experiments of D.K. Belyaev and his colleagues on the domestication of foxes ( Tinder, 2007). In these experiments, foxes were selected for reduced aggressiveness. The result was friendly animals that retained some “childlike” characteristics into adulthood, such as drooping ears and a shortened muzzle. It seems that selection for friendliness (in many animals this is a “childish” trait) can, as a side effect, lead to the juvenileization of some other features of morphology, thinking and behavior. These signs may be interrelated - for example, through hormonal regulation.

So far, we cannot say for sure how relevant the selection for reduced aggressiveness was in our ancestors and whether our juvenile features (high forehead, shortened facial part of the skull, the nature of the hairline, curiosity) can be explained by such selection. But the assumption looks tempting. Apparently, the reduction of intragroup aggression played an important role in the early stages of hominid evolution. But there are also many facts that indirectly indicate, on the contrary, an increase in hostility between groups of hunter-gatherers (and this is considered as one of the reasons for the development of intra-group cooperation; we will return to this topic in the chapter “The Evolution of Altruism,” Book 2). But in this case we are already talking about the later stages of evolution and intergroup aggression. So these hypotheses do not contradict each other.

Australopithecus

Let's get back to history. If a long series of lyrical digressions did not confuse the reader, then he still remembers that we settled on Ardipithecus, who lived in East Africa 4.4 million years ago. Shortly thereafter, approximately 4.2 million years ago, Ardi's successors appeared on the African scene - slightly more "advanced", slightly more "human" bipedal apes, united by most anthropologists in the genus Australopithecus. The oldest known species of this genus, Australopithecus anamensis ( Australopithecus anamensis, 4.2–3.9 million years ago), described from fragmentary material. Therefore, it is difficult to say anything definite about him except that his structure was indeed intermediate between Ardipithecus and the later - and better studied - Australopithecus. He could very well be a descendant of Ardi and an ancestor of Lucy.

Australopithecus afarensis, the species to which Lucy belonged, lived in East Africa from approximately 4.0 to 2.9 million years ago. Remains of many individuals of this species have been found. A. afarensis almost certainly was among our ancestors, or at least was very closely related to them. Primitive characteristics (for example, a brain with a volume of only 375–430 cm 2, like a chimpanzee) were combined with advanced, “human” ones (for example, the structure of the pelvis and lower limbs, indicating upright walking).

Lucy, described in 1978 by Donald Johanson, Tim White and Yves Coppin, was described in detail by Johanson himself in the book Lucy: The Origins of the Human Race. This book was published in Russian in 1984. We will limit ourselves to a brief story about two new important finds.

The search for hominid fossils in East Africa - the cradle of humanity - has long ceased to be the preserve of lone enthusiasts. The work is carried out on a grand scale, promising areas are divided between competing groups of anthropologists, excavations are carried out systematically and very purposefully. In 2000, in one of these “research areas” - in Dikika (Ethiopia) - a unique discovery was made: a well-preserved skeleton of a young Australopithecus afarensis, most likely a three-year-old girl who lived 3.3 million years ago. Anthropologists have given her the unofficial nickname “Daughter Lucy” ( Alemseged et al. 2006; Wynn et al., 2006). Most of the bones were buried in hard sandstone, and it took a full five years to dissect the skeleton (cleaning the bones from the surrounding rock).

The Dikika area, and especially those layers in which the skeleton was found, have been thoroughly studied paleontologically, which made it possible to reconstruct the habitat of “Lucy’s daughter.” It looks like it was a paradise: a river valley with lush floodplain vegetation, lakes, a mosaic landscape with alternating forest areas and open spaces, an abundance of herbivores, including large ones, characteristic of both forest and steppe habitats (antelope, rhinoceroses, hippopotamuses , fossil three-toed hipparion horses, many elephants), and an almost complete - as far as can be judged from fossil remains - absence of predators (only numerous bones of a large fossil otter were found Enhydriodon and a lower jaw, possibly belonging to a raccoon dog). In general, there was less forest and more savanna than in the habitats of the more ancient hominids - Ardipithecus, Australopithecus anamas and Kenyanthropus.

Australopithecus afarensis is one of the most well-studied hominid species. Its remains have been found in many places in Ethiopia, Kenya and Tanzania. The Hadar site alone in central Ethiopia has yielded bones from at least 35 individuals. However, before they found and dissected “Lucy’s daughter,” scientists knew almost nothing about how these monkeys developed and what their children looked like.

The geological age of the find (3.31–3.35 million years) was determined by the stratigraphic method [Stratigraphy is the science of dividing sedimentary rocks into layers, determining their relative geological age (as a rule, young layers lie on top of older ones) and the correlation (correlation with each other) of coeval layers from different places and sedimentary strata. To correlate layers, many methods are used, including paleontological (comparison of complexes of fossil remains of living organisms)]. This means that, based on a complex of paleontological and other characteristics, the rock in which the skeleton was found was assigned to a strictly defined stratigraphic horizon (layer), the absolute age of which was previously established using several independent radiometric methods [For more information on methods for determining the age of rocks and the fossils contained in them, see: Markov A.V. Chronology of the distant past].

The individual age of the girl herself (about three years) was determined by her teeth. In addition to well-preserved baby teeth, computed tomography revealed emerging adult teeth in the jaws. Their shape and relative sizes made it possible to determine the sex of the child (it is known that in Australopithecus afarensis, men and women differed from each other in a number of characteristics, including teeth, more than in later hominids).

The authors of the find compared it with another young australopithecus - the “child from Taung”, found in the 1920s in South Africa by Raymond Dart (this is where the study of australopithecus began). The "Child from Taung" lived much later and belonged to a different species - Australopithecus africanus. It turned out that the girl from Dikika, despite her young age, already had a number of characteristic distinctive features of her species A. afarensis, so its species identity is beyond doubt.

The girl's brain volume is estimated at 275–330 cm3. This is slightly smaller than would be expected based on the average brain volume of adult australopithecines. Perhaps this indicates a slightly slower brain growth compared to modern apes. Very rarely preserved in fossil hominids, the hyoid bone is similar to that of young gorillas and chimpanzees and is very different from that of humans and orangutans. This is an argument in favor of the absence of speech in Australopithecus, which, however, did not raise much doubt [The question of the origin of speech in hominids is discussed in detail in the book by S. A. Burlak “The Origin of Language” (2011), so here we hardly touch on this topic].

The girl's legs, like those of other Australopithecus afarensis, have many advanced ("human") features. This once again confirms that A. afarensis was an upright walking creature. The bones of the arms and shoulder girdle, according to the authors, bring the young Australopithecus closer to a gorilla than to a human, although some shift towards the “human” side is still observed.

In general, the find confirmed the “functional dichotomy” of the structure of Australopithecus afarensis: a very advanced, almost human lower part of the body was combined with a relatively primitive, “ape-like” upper part. Some researchers interpreted this “monkey top” simply as a legacy of their ancestors, which the australopithecus had not yet managed to get rid of, while others interpreted it as evidence of a semi-arboreal lifestyle. However, both interpretations may well be correct at the same time.

"Daughter Lucy's" shoulder blade - the first complete shoulder blade found A. afarensis- only made things more confusing, since it resembles a gorilla's shoulder blade (or rather, it looks like something between a gorilla and a human shoulder blade), and gorillas are not the biggest fans of climbing trees. They actively use their hands when walking, resting on their knuckles, just like chimpanzees. The authors who described Lucy's daughter are still inclined to believe that Australopithecus afarensis spent a lot of time in trees and therefore retained adaptations for climbing.

Various combinations of primitive and advanced characters are generally very characteristic of fossil organisms, whose primitiveness and advancedness we evaluate in hindsight - by comparison with distant descendants and ancestors. Evolutionary changes in different organs and parts of the body always occur at different speeds - there is simply no reason why they should all change absolutely synchronously. Therefore, no matter what transitional form we take, it will always turn out that some characteristics are already “almost like those of the descendant,” while others are still “exactly like those of the ancestor.”

Juvenile Australopithecines were prey to birds of prey

Australopithecus africanus ( Australopithecus africanus) lived in South Africa between 3.3–3.0 and 2.4 million years ago. It was with this species that the study of Australopithecus began.

The famous "Taung Child" skull was found by a lime mine miner in South Africa in 1924. The skull fell into the hands of Raymond Dart, one of the pioneers of paleoanthropology. The very next year, a sensational article by Dart appeared in the journal Nature, entitled “Australopithecus africanus: an ape from South Africa” ( Dart, 1925). This is how humanity first learned about Australopithecines - the long-awaited “missing link” between monkeys and Pithecanthropus, already known by that time ( Homo erectus).

Along with the skull of a young Australopithecus, bones of baboons, antelopes, turtles and other animals were discovered in Taung Cave. The baboons' skulls looked as if they had been crushed by some blunt instrument. Dart suggested that all this fauna was the remains of the feasts of the apes. This is how the image of Australopithecus arose - a skilled hunter who ran across the savannah after baboons and killed them with a blow to the head with a club. Subsequently, adults were also found A. africanus, also in association with a diverse fossil fauna.

A detailed study of these paleocomplexes led scientists to the conclusion that the found accumulations of bones are indeed the remains of feasts, but not of apes, but of some other predators. Australopithecus turned out to be not hunters, but prey. Suspicion initially fell on large cats, such as the saber-tooth Meganthereon ( Megantereon). Leopards and spotted hyenas were also named as possible hunters of apes. These assumptions were based, in particular, on a comparison of the trace element and isotopic composition of the bones of predators and ancient hominids, as well as on the characteristic damage on the bones of the latter, exactly corresponding to the fangs of a leopard.

In 1995, it was first suggested that the “Child from Taung,” along with baboons and other animals, fell victim to a large bird of prey, similar to the modern African crowned eagle ( Berger, Clarke, 1995). The hypothesis has been heavily criticized. In particular, the opinion was expressed that not a single eagle is able to lift such large prey into the air as a baby Australopithecus.

In recent years, much more has become known about the habits of large birds of prey - monkey hunters. For example, it turned out that the lifting power of these birds has until now been greatly underestimated. However, the “bird hypothesis” lacked decisive evidence - clear traces that the “child from Taung” had been in the claws of a huge eagle. Such evidence was obtained in 2006, after the skulls of modern monkeys killed by the crowned eagle were examined in detail. Having familiarized himself with the new data, South African anthropologist Lee Berger, one of the authors of the “bird hypothesis,” drew attention to the description of characteristic holes and breaks in the upper parts of the eye sockets left by eagle claws. The scientist immediately reexamined the skull of the “child from Taung” and found the same damage in both eye sockets.

No one paid attention to them, which is not surprising - after all, until now these damages would still not have been interpreted. In the right eye socket of the “child from Taung” there is a noticeable round hole with a diameter of 1.5 mm, in the upper part of the left eye socket there is a large hole with jagged edges. Together with a dent on the top of the skull described in 1995, these injuries are sufficient evidence that the juvenile australopithecus was captured, killed and eaten by a large bird of prey.

Berger points out that eagles were most likely not the only enemies of australopithecines. Four-legged and feathered predators are the most important factor in mortality in modern African apes, and, apparently, things were no better among our distant ancestors. Many anthropologists consider the threat from predatory animals and birds to be one of the important reasons for the development of sociality in ancient hominids (and high sociality, in turn, could contribute to the accelerated development of the mind), therefore, in order to understand the evolution of our ancestors, it is important to know who hunted them ( Berger, 2006).

The point of view about the semi-arboreal life of Australopithecus afarensis, as well as about their not entirely human, clumsy gait, has recently been disputed by many anthropologists. This is supported by new data obtained during the study of the famous footprints from Laetoli (Tanzania), as well as the recent discovery of the postcranial skeleton of a very large representative A. afarensis- A big man.

Traces of Laetoli were discovered by Mary Leakey in 1978. This is a chain of traces of three hominids imprinted in ancient volcanic ash: two adults and one child. The oldest traces of bipedal primates glorified not only Mary Leakey herself, but also the place of discovery - the village of Laetoli, located in East Africa, Tanzania, in the Ngorongoro Nature Reserve. On the edge of the Serengeti plateau, not far from Laetoli, there is the now extinct Sadiman volcano - it was its ashes that immortalized the traces of australopithecines.

The volcanic eruption that these three may have been trying to escape from occurred 3.6 million years ago. In those parts, of the hominids known to science, only Australopithecus afarensis lived then. Most likely, they left traces. From the prints of their feet it is clear that their big toe was no longer opposed to all the others, like Ardi’s, but was adjacent to them - almost like ours. This means that Australopithecus afarensis said goodbye to the old ape custom of grabbing branches with their feet.

But how did they walk - did they lumber clumsily, half-bent, like modern gorillas or bonobos, when they find it a whim to walk “without arms”, or with a confident, firm gait, straightening their legs - like humans? Recently, American anthropologists have taken up this issue seriously ( Raichlen et al., 2010). They forced human volunteers to walk in different gaits on the sand, distributing their body weight differently and placing their feet differently, and then compared the resulting tracks with the tracks from Laetoli. Conclusion: the gait of Australopithecus afarensis was practically no different from ours. They walked confidently and moved their legs like us, fully straightening their knees.

A large Australopithecus afarensis, nicknamed Kadanuumuu (which means big man in the local dialect), was described in 2010 by a group of anthropologists from the United States and Ethiopia ( Haile-Selassie et al., 2010). The research team included Owen Lovejoy, already known to us. The find was made in the Afar region of Ethiopia, the same place where many other hominid fossils originate. The skull was never found, but the bones of the left leg and right arm (without the foot and hand), a significant part of the pelvis, five ribs, several vertebrae, the left collarbone and the right shoulder blade were found. Most likely, it was a male (or is it time to say a man?), and a very large one. If Lucy's height was about 1.1 m, then the Big Man was about half a meter taller, that is, his height was within the normal range of modern people. He lived 3.6 million years ago - 400,000 years before Lucy and almost simultaneously with three unknown people who left traces on the volcanic ash in Laetoli.

The structure of the skeleton of the Big Man, according to the authors, indicates a high adaptability to full bipedal walking and the absence of adaptations for tree climbing. Kadanuumuu's shoulder blade is much less gorilla-like than Lucy's shoulder blade, and looks almost human. From this, the authors conclude that the Big Man knew how to climb trees a little better than us. The ribs, pelvis and limb bones also show many advanced features. Even the ratio of the lengths of arms and legs, although with difficulty, fits into the range of normal variability Homo sapiens. Among modern people there are few such long-armed and short-legged individuals, but they still come across. Apparently, this means that Australopithecus afarensis was quite variable in the size and proportions of its body - perhaps almost the same as modern humans. Characteristics that were previously conventionally considered to be common to all Afar people (for example, very short legs, like Lucy’s) could in fact depend on age, gender and vary widely within the population.

As for sexual dimorphism (differences in body size and proportions between men and women), there is fierce debate about this. Some authors (perhaps the majority) believe that dimorphism in Australopithecus afarensis was much more pronounced than in modern humans. In apes, strong sexual dimorphism (with males much larger than females) is a sure sign of a harem system, which would seem to contradict the supposed monogamy of australopithecines. Other authors, including Lovejoy, argue that sexual dimorphism among the Afar people was about the same as ours. Of course, the discussion is not based on reasoning, but on real bones and careful measurements, but the collected material, apparently, is still not enough for reliable conclusions.

According to anthropologist S.V. Drobyshevsky (2010, who studied a large number of endocranes (casts of the brain cavity) of fossil hominids, the brain of australopithecus was similar in structure to the brain of chimpanzees, gorillas and orangutans, but differed in a more elongated shape due to an enlarged parietal lobe. Perhaps this was due to the fact that australopithecines had greater mobility and sensitivity in their hands, which is actually logical, given their walking style.

Paranthropus

Paranthropus, also called massive australopithecines, is one of the dead-end branches on the hominid evolutionary tree. Three types of paranthropes have been described: P. aethiopicus(2.6–2.3 million years ago, East Africa), R. boisei, aka Zinjanthropus (2.3–1.2 million years ago, East Africa), and P. robustus(1.9–1.2 million years ago, South Africa). They lived simultaneously with other representatives of hominids - ordinary, or gracile (more miniature), australopithecines, such as A. garhi from East Africa and South African A. sediba, and the most ancient representatives of the human race ( Homo).

In the initial period of their history, representatives of the human race lived in Africa, surrounded by a variety of relatives who differed from ancient people much less than modern chimpanzees differ from modern humans. Interspecific relationships within the hominid group undoubtedly left their mark on the early stages of human evolution. The presence of several closely related species in one territory probably required the development of special adaptations to prevent interspecific hybridization and to separate ecological niches (it is difficult for closely related species to live together if their diets and lifestyles are the same). Therefore, to understand the early stages of the history of the family Homo It's important to know how our extinct bipedal cousins ​​lived and ate—even if we know they weren't our ancestors.

Paranthropus appears to have evolved from the common, or gracile, australopithecines (like the first humans), but their evolution went in a different direction. First Homo included the remains of predators' meals in their diet and learned to scrape off leftover meat and split bones using primitive stone tools; their brain began to enlarge, and their jaws and teeth, on the contrary, gradually became smaller. Paranthropus went a different way: their brain remained small (much like that of chimpanzees and gracile australopithecines), but their teeth, jaws and chewing muscles reached a level of development unprecedented for hominids. The fangs, however, remained relatively small: this was probably irreversible.

Traditionally, it was believed that the driving force behind these changes was adaptation to feeding on rough plant foods—tough roots, stems, leaves, or hard-shelled nuts. Based on morphological data, scientists reasonably believed that Paranthropus were specialized consumers of the toughest and hardest food items, inaccessible to other hominids due to the relative weakness of their jaws and teeth. It was also assumed that narrow food specialization may have been one of the reasons for the extinction of Paranthropus. The first people, on the contrary, retained the omnivorous nature of their ancestors, the gracile australopithecines. It is clear that omnivorous forms have a better chance of surviving environmental changes than narrow specialists. History repeated itself in later times, when a highly specialized species of people that ate mainly meat - the Neanderthals - was supplanted by the omnivorous Homo sapiens [Only at the end of 2010 did it become clear that neither Asian nor European Neanderthals were in fact 100% meat eaters, as seemed to follow from the isotopic composition of tooth enamel. Starch granules have been found in Neanderthal tartar, indicating that they occasionally ate barley, dates, legumes (in Asia), water lily rhizomes, and possibly cereals (in Europe). Moreover, judging by the shape of these granules, Neanderthals even knew how to cook plant foods] (Dobrovolskaya, 2005).

Subsequently, facts were discovered that contradict the hypothesis about the narrow food specialization of Paranthropes. Analysis of the isotopic composition of tooth enamel showed that they apparently were omnivores ( Lee-Thorp et al., 2000). In particular, their diet included termites, which Paranthropus mined using primitive bone tools ( d"Errico, Backwell, 2009).

But the opinion remained unshakable that rough plant food constituted an important part of the diet of paranthropes. Otherwise, why would they have such powerful jaws and huge teeth? However, in 2008, this seemingly self-evident assumption was also questioned ( Ungar et al., 2008).

American anthropologists studied microscopic traces of wear on tooth enamel preserved on the molars of seven individuals. Paranthropus boisei. This species lived in the East African savanna, often near rivers and lakes. The specialization features characteristic of Paranthropus (large flat molars, thick tooth enamel, powerful chewing muscles) are most strongly expressed in this species. It is not surprising that the first skull of this species found was nicknamed the Nutcracker. Of the 53 individuals studied, details of the structure of the dental surface were well preserved in only seven. However, these seven individuals are a fairly representative sample. They come from three countries (Ethiopia, Kenya, Tanzania) and cover most of the existence of this species. The oldest of the skulls is about 2.27 million years old, the youngest is 1.4 million years old.

The authors used two characteristics of the enamel surface that reflect the nature of food preferences: fractal complexity (the variety of sizes of microscopic depressions and grooves) and anisotropy (the ratio of parallel and randomly oriented microscratches). Studies of the teeth of modern primates on different diets have shown that high fractal complexity is associated with feeding on very hard foods (e.g., crunching nuts), while high anisotropy reflects feeding on tough foods (roots, stems, leaves). It is important that traces of microwear of tooth enamel are ephemeral - they do not accumulate throughout life, but appear and disappear in a few days. Thus, from these traces one can judge what the animal ate in the last days of its life. For comparison, the authors used the teeth of four species of living primates whose diet includes hard and tough objects, as well as two fossil hominids: Australopithecus africanus and Paranthropus robustus.

The results surprised the researchers. Scratched tooth enamel R. boisei turned out to be very low. No signs of feeding on particularly hard or tough objects could be found. Modern solid-fed apes exhibit markedly higher fractal complexity, and hard-fed primates exhibit higher anisotropy.

Nutcrackers rarely seemed to chew nuts or chew tough vegetation. They preferred something softer and more nutritious - for example, juicy fruits or insects. At least none of the seven individuals studied ate anything hard or tough in the last days before death. The surface texture of their tooth enamel is similar to that of soft fruit-eating monkeys.

Previously, a similar analysis was carried out for another species of Paranthropus - the South African P. robustus. It turned out that this species also did not always eat hard and tough objects - apparently, only at certain times of the year ( Scott et al., 2005). It's amazing that P. boisei, whose teeth and jaws are more developed than those of P. robustus, ate solid foods less often. He seemed to eat hard food more often than R. robustus, but not more often than gracile australopithecus Australopithecus africanus, which did not have such powerful teeth and jaws as those of Paranthropus.

It turns out that Paranthropus preferred to eat something completely different from what their teeth and jaws were adapted to. This seems paradoxical - and indeed, this phenomenon is known to science as Liam's paradox. A discrepancy between morphological adaptations and actual food preferences sometimes occurs, for example, in fish, and the reasons for this phenomenon are now generally understood ( Robinson, Wilson, 1998). This happens when the preferred types of food are easily digestible and do not require the development of special adaptations, but sometimes there is not enough “good” food, and then animals have to switch to other, lower quality or poorly digestible food. During such critical periods, survival will depend on the ability to effectively obtain and assimilate “bad” food—one that the animal would not come close to under normal conditions. Therefore, there is nothing unnatural in the fact that some animals have developed morphological adaptations to feeding on foods that they do not usually eat. Something similar is observed in some modern primates - for example, gorillas, who prefer fruits, but in times of famine switch to hard leaves and shoots.

Perhaps Paranthropus represents one example of Liam's paradox. Hominids can eat soft fruits or insects with any teeth and jaws, but chewing hard roots during periods of hunger requires large teeth and powerful jaws. Even if such hunger strikes occur rarely, it is enough for natural selection to begin to favor stronger teeth and jaws.

Most likely, sexual selection could not have happened here - especially considering the latest data that Paranthropus had highly developed sexual dimorphism, males were much larger than females and had harems (see below). Powerful jaws and teeth could increase a male's chances of winning in competition with other males and increase their attractiveness in the eyes of females. Our ancestors obviously had different tastes. They were attracted to something else in males - maybe caring, the ability to get a tasty brain bone for their beloved from under the noses of hyenas and vultures, complex and inventive behavior during courtship?

Thus, not only were Paranthropus not food specialists, they may have been even more omnivorous than the gracile australopithecines. After all, the latter, it seems, could not feed on the tough parts of plants, but Paranthropus could, although they did not like it. On the other hand, all the food resources available to gracile Australopithecus were also available to Paranthropus. If food specialization increases the likelihood of extinction, then it would be more likely to expect Paranthropus to survive and the line of gracile australopithecines to be extinguished. This did not happen, probably, only because the descendants of the gracile australopithecines - the first people - found another, more versatile and promising way to expand their diet. Instead of powerful teeth and jaws, sharp stones, complex behavior and a smart head were used; instead of tough and inedible roots, meat and bone marrow of dead animals were used.

The results obtained, among other things, show that the structure of teeth and jaws alone cannot be used to judge with certainty the diet of extinct animals. Morphological adaptations may sometimes reflect not a preferred diet, but rather ways of feeding that the animal would normally try its best to avoid.

In recent years, scientists have managed to find out something about the social life of paranthropes. Anthropologists from South Africa, Great Britain and Italy have come up with a new method of comparative analysis of fossil bones to help understand how males and females of extinct hominids developed after they reached sexual maturity. The fact is that in modern primates that practice the harem type of family relationships (for example, gorillas and baboons), females, having reached maturity, almost no longer grow, while males continue to grow for quite a long time. This is due to the fact that in such species there is very strong competition between males for the right to access the group of females. Young males have almost no chance of success in the fight against mature individuals, so they postpone decisive action until they reach full strength.

In harem species, mature males are much larger than both females and young mature males; Often they also differ in color. In species that practice more democratic family relationships, such as humans and chimpanzees, sexual dimorphism is less pronounced (males are not so different from females in size and color), and in males the achievement of sexual and social maturity approximately coincides in time. In this case, the period of “additional” growth of sexually mature males is reduced or not expressed.

The researchers reasoned that if the size of the individuals (determined by bone size) was compared with their age (determined by tooth wear), then, with sufficiently abundant material, it would be possible to understand how long the males of a given species continued to grow after reaching sexual maturity. South African species Paranthropus robustus attracted the attention of researchers primarily due to the abundance of material. The authors examined fragments of the skulls of 35 individuals and selected 19 of them for their analysis.

Three selection criteria were used: 1) erupted wisdom teeth – evidence of puberty; 2) the preservation of a significant part of the facial or jaw bones, so that the size of the individual can be estimated; 3) well-preserved molars, so that age can be assessed by the wear of the enamel.

It turned out that the sample studied was divided into two unequal parts. In the first of them (four individuals), body size did not increase with age—there was no stage of “additional” growth. The researchers determined that these were females. In the second group (15 individuals) there was growth, and quite significant. These are most likely males. Young males differed little in size from females, while mature males were much larger. This suggests that Paranthropus had harems, and there was intense competition between males for females.

A natural question arises: why have so many more male skulls been found than female ones? The authors give an elegant answer to this, thanks to which the unequal sex ratio among the found skulls becomes additional confirmation of the proposed theory. The fact is that the examined skulls belong mainly to those individuals that fell victims to predators. For example, the location of bones in the Swartkrans cave, where many bone remains were found P. robustus, is considered a classic example of a fossil assemblage formed as a result of the activity of predators. Many of the bones from Swartkrans bear unambiguous traces of teeth.

Why did male Paranthropus fall into the clutches of saber-tooths or hyenas three times more often than females? It turns out that this is precisely the picture observed in modern “harem” primates. Females of these species always live in groups, usually under the protection of a seasoned “husband,” while males, especially young ones who have not yet managed to acquire their own harem, roam alone or in small groups. This significantly increases the chances of being eaten by a predator. For example, male baboons during their solitary life are three times more likely to become victims of predators compared to females and males living in a group.

The authors also analyzed material on South African gracile australopithecines ( A. africanus), which are closer to human ancestors than Paranthropus. The material on this species is not so rich, and therefore the conclusions are less reliable. However, judging by the available facts, A. africanus sexual dimorphism was much less pronounced than in Paranthropus, and females and males became victims of predators with approximately the same frequency. This is an additional argument in favor of the fact that gracile australopithecines did not have a harem system and family relationships were more equal ( Lockwood et al., 2007).

The increased mortality of young males in a harem system is unlikely to benefit the group and the species as a whole. This can be seen as one of the reasons why Paranthropus ultimately lost the evolutionary competition to its closest relatives - the gracile australopithecines and their descendants, humans.

Great apes, or ( Hominoidae) is a superfamily of primates, which includes 24 species. Although people treat Hominoidea, the term "ape" does not apply to humans and describes non-human primates.

Classification

Apes are classified in the following taxonomic hierarchy:

• Domain: ;
• Kingdom: ;
• Type: ;
• Class: ;
• Squad: ;
• Superfamily: Hominoids.

The term ape refers to a group of primates that includes the families: hominids (chimpanzees, gorillas, orangutans) and gibbons. Scientific name Hominoidea refers to apes (chimpanzees, gorillas, orangutans, gibbons) as well as humans (i.e., it ignores the fact that humans prefer not to call themselves apes).

The gibbon family is the most diverse, with 16 species. Another family, the hominids, is less diverse and includes: chimpanzees (2 species), gorillas (2 species), orangutans (3 species) and humans (1 species).

Evolution

The record is incomplete, but scientists believe that ancient hominoids diverged from the apes between 29 and 34 million years ago. The first modern hominoids appeared about 25 million years ago. Gibbons were the first group to diverge from other groups, about 18 million years ago, followed by the lineage of orangutans (about 14 million years ago), and gorillas (about 7 million years ago).

The most recent split occurred between humans and chimpanzees about 5 million years ago. The closest living relatives of hominoids are the Old World monkeys, or marmosets.

Environment and habitat

Hominoids live throughout the Western and Central regions, as well as in the Southeast. Orangutans are found only in Asia, chimpanzees inhabit Western and Central Africa, gorillas are common in Central Africa, and gibbons live in Southeast Asia.

Description

Most hominoids, with the exception of humans and gorillas, are skilled as well as flexible climbers. Gibbons are the most agile arboreal primates of all hominids. They can jump along branches, moving quickly and efficiently through trees.

Compared to other primates, hominoids have a lower center of gravity, a shortened spine relative to their body length, a wide pelvis, and a broad chest. Their overall physique gives them a more upright posture than other primates. Their shoulder blades are located on their back, allowing for a wide range of motion. Hominoids also do not have a tail. Together, these characteristics give hominoids a better balance than their closest living relatives, the Old World monkeys. Hominoids are therefore more stable when standing on two legs or swinging their limbs, and hanging from tree branches.

Hominoids are very intelligent and capable of problem solving. Chimpanzees and orangutans make and use simple tools. Scientists studying orangutans in captivity have noted the primates' ability to use sign language, solve puzzles, and recognize symbols.

Nutrition

The diet of hominoids includes leaves, seeds, nuts, fruits and a limited number of animals. Most species, but fruits are the preferred food. Chimpanzees and orangutans primarily eat fruit. When gorillas lack fruit at certain times of the year or in certain regions, they feed on shoots and leaves, often bamboo. Gorillas are well adapted to chew and digest such a low-nutrient food, but these primates still prefer fruit when it is available. Hominoid teeth are similar to those of Old World monkeys, although they are especially large in gorillas.

Reproduction

Gestation in hominoids lasts from 7 to 9 months and leads to the birth of one offspring or, less commonly, two. The cubs are born helpless and require care for a long time. Compared to most other mammals, hominoids have a surprisingly long period of breastfeeding. In most species, full maturity occurs at the age of 8-13 years. As a result, females typically give birth only once every few years.

Behavior

Like most primates, hominoids form social groups, the structure of which varies among species. Gibbons form monogamous pairs. Orangutans are an exception to the social norm of primates; they lead a solitary life.

Chimpanzees form groups that can number from 40 to 100 individuals. Large groups of chimpanzees break up into smaller groups when fruit becomes less available. If small groups of dominant male chimpanzees go off to find food, the females will often copulate with other males in their group.

Gorillas live in groups of 5 to 10 or more individuals, but they remain together regardless of the availability of fruit. When fruits are difficult to find, they resort to eating leaves and shoots. Because gorillas stay together, the male is able to monopolize the females in his group. This fact is associated with more in gorillas than chimpanzees. In both chimpanzees and gorillas, groups include at least one dominant male, with females leaving the group in adulthood.

Threats

Many hominoid species are endangered due to extermination, poaching, and hunting for bushmeat and skins. Both chimpanzee species are critically endangered. Gorillas are on the verge of extinction. Eleven of the sixteen gibbon species are becoming extinct.

There is little doubt that hominoids - the great apes - originated in Africa, and for almost 10 million years their history was exclusively associated with this continent.

One of the earliest hominoids is a monkey found in East Africa, the so-called proconsul. The age of these remains is approximately 25 million years. But soon other representatives of great apes appeared in Africa: dryopithecus, micropithecus, afropithecus, etc. Their body weight varied from 3 to 150-170 kg (the weight of a female gorilla), they ate mainly fruits and young leaves. Scientists were lucky enough to find limb bones of some of them, thanks to which we know that hominoids walked on four legs and led a predominantly arboreal lifestyle.

Approximately 16-17 million years ago, when a land bridge was formed between Africa and Eurasia, the habitat of hominoids expanded significantly - they moved to the south of Europe and Asia. The most ancient fossil representatives of this group in Europe date back to 13-15 million years, and in Asia - about 12 million years. However, if in Asia, at least in its southeastern regions, they managed to thoroughly gain a foothold (and to this day great apes - orangutans and gibbons live there), then in Europe the conditions for them turned out to be less suitable, and, having experienced a “heyday ", hominoids went completely extinct about 8 million years ago. And although the number of ape species also declined significantly in Africa between 15 and 5 million years ago, it was this continent that remained the arena on which the main events of the drama called “Human Evolution” unfolded.

Here we will have to introduce a new term - hominids (not to be confused with hominoids!). The word “hominids” can be translated as “human” (not “humanoid”!). This term is usually understood to mean a person and all his supposed “lineal ancestors.” This means that from the several representatives of fossil apes known to us, we need to choose the one who followed the path of “humanization” - in contrast to all the others who “transformed” into modern apes - chimpanzees, gorilla, orangutan and gibbon. History has given us several candidates to choose from (which we can most often judge only from small fragments of bones).

Dryopithecus. These “tree monkeys” (drio means “tree” and nitek means “monkey”) lived in southern Asia, southern Europe, and Africa more than 15 million years ago. They were roughly the size of modern baboons or chimpanzees.

Ramapithecus, which succeeded Dryopithecus and existed for almost 10 million years, was named after the Hindu deity Rama. The first discovery was made in India among the Siwalik hills. A similar creature was also found in Kenya, and it was decided that it belongs to the same species as Ramapithecus. For some time, scientists saw Ramapithecus as our first hominid ancestor, but it is now believed that Ramapithecus most likely belongs to a side branch of evolution that ultimately led to the emergence of the orangutan, and not humans at all.

Sivapithecus got its name from the Hindu god Shiva (their bones were also first found in India). We have a very vague idea of ​​how they looked and moved.

Udabnopithecus - its bone remains (two teeth and a fragment of the upper jaw) were found in the Udabno area in South-Eastern Georgia. He lived about 15 million years ago.

Oreopithecus is much closer to our time - it is “only” about 7.5 million years old. It is known about him that he could live not in trees, but on the ground, but most likely he still moved on four limbs. Currently, most scientists believe that Oreopithecus eventually went extinct.

So, at different times, different fossil apes were considered candidates for the role of our direct ancestor, and this question has not yet been finally resolved. Unfortunately, we know almost nothing about the structure of the arms and legs of most of these monkeys - but this is very important to know in order to decide whether any of them had at least some ability to move on two rather than four limbs. Thus, the vacancy of the founder of the hominid family still remains vacant. True, there is still one contender to take it. This is Ouranopithecus, whose bones were discovered in northern Greece; its approximate age is 10 million years. According to experts, this creature could well have become the ancestor of both modern apes and humans.

When did our ancestors and the ancestors of modern apes diverge? An unusually complex genetic method - comparing human and ape DNA - showed that this happened 8-4 million years ago. Moreover, most likely, first the ancestors of the gorilla, and then the chimpanzee, separated from the main trunk. This means that we have a closer family relationship with chimpanzees. DNA comparisons between humans and chimpanzees indicate that their last common ancestor lived approximately 5.5 to 4 million years ago. This date generally does not contradict the data available today on bone finds.

One of these finds is the remains of a skeleton found in the town of Aramis in Ethiopia, in a geological layer that formed about 4.4 million years ago. At first, scientists decided that these bones belonged to the most ancient species of australopithecus (which will be discussed later), and called it Australopithecus ramidus (Australopithecus ramidus). But a few months later, the authors of the first description of the bones from Aramis considered that this creature still had not yet “grown up” to Australopithecus, and published an amendment in which it was presented to colleagues under the “name” Ardipithecus ramidus (Ardipithecus ramidus). One way or another, this same ramidus has not yet been properly studied, and practically nothing is known about its supposed contemporaries and, especially, predecessors.

The main source of information about the earliest stages of human origins were and remain the bones of australopithecines, of which, fortunately, quite a lot were preserved in sediments aged from 3.8 to 2 million years, and every year there are more and more new finds.

CONTROL TESTING AT THE RESULTS OF THE 3RD QUARTER

Grade: ninth

Program by I.N. Ponomareva

For each question, choose ONE correct answer.

1.Which hypothesis states that life on Earth was brought from space?

1) in the hypothesis of biochemical evolution

2) in the stationary state hypothesis

3) in the genetic hypothesis

4) in the panspermia hypothesis

2.What are coacervates?

1) nucleic acid complexes

2) protein complexes

3) fat complexes

4) spontaneously concentrating complexes of primary organic substances

3.What are the names of organisms that feed on ready-made organic substances?

1) protobionts

2) chemotrophs

3) heterotrophs

4) autotrophs

4.Which organisms capable of photosynthesis are the most ancient?

1) viruses

2) plants

3) green euglena

4) cyanobacteria

5.What are the names of organisms that themselves synthesize organic substances from inorganic ones?

1) autotrophs

2) heterotrophs

3) protobionts

4) chemotrophs

6.What is the largest unit of geological chronology called?

1) era

2) period

3) era

4) century

7.Which animals were the first to master land?

1) dinosaurs

2) turtles

3) crocodiles

4) Cancerscorpios

8. How many eras are there in the history of the development of our planet?

1) five

2) six

3) seven

4) eight

9.Which era continues at the present stage of the Earth’s development?

1) Proterozoic

2) Paleozoic

3) Mesozoic

4) Cenozoic

10.What, according to Charles Darwin, is the main driving force of evolution?

1) natural selection

2) heredity

3) artificial selection

4) variability

11.What set of individuals is considered to be the elementary unit of evolution?

1) view

2) population

3) family

4) gender

12.What teaching claimed that the origin and diversity of the world is the result of the divine will?

1) creationism

2) vitalism

3) Lamarckism

4) neo-Lamarckism

13.Which type criterion is the most accurate?

1) environmental

2) genetic

3) morphological

4) geographical

14.What phenomenon did Charles Darwin explain the emergence of different types of finches on the Galapagos Islands?

1) microevolution

2) macroevolution

3) allopatric speciation

4) sympatric speciation

15.What process refers to biological regression?

1) increase in the number of species

2) increase in the area of ​​distribution of the species

3) increasing the adaptability of individuals to environmental conditions

4) decrease in the adaptability of individuals to the environment

16.Which process does NOT belong to aromorphoses?

1) the appearance of warm-bloodedness

2) the appearance of seeds in plants

4) the emergence of the brain

1) gender

2) family

3) class

4) department

18.What refers to biological progress?

1) decrease in the number of species

2) increase in the number of species

3) decrease in the adaptability of individuals to the environment

4) reduction in the area of ​​distribution of the species

19.Which process does NOT belong to idioadaptation?

1) the appearance of wings in birds

2) a wide variety of pollination methods in angiosperms

3) ecological differentiation of finch beaks

4) formation of protective coloring

20.What was the name of the group of apes, consisting of the earliest primates?

1) anthropoids

2) pongids

3) hominids

4) tarsiers

21.What biological feature does NOT characterize the species Homo sapiens?

1) large brain volume

2) strong jaws

3) predominance of the cerebral part of the skull over the facial part

4) upright posture

22.What were the names of the extinct arboreal apes, the ancestors of modern apes and humans?

1) hominids

2) tarsiers

3) Dryopithecus

4) pongids

23.Which scientist was the first to prove in his work that humans are related to apes?

1) C. Linnaeus

2) T. Huxley

3) J.B. Lamarck

4) Charles Darwin

24.What modern people appeared on Earth 40-30 thousand years ago and continue to live today?

1) neoanthropes

2) archanthropes

3) Neanderthals

4) paleoanthropes

25.How is the word “australopithecus” translated from Latin?

1) Australian monkey

2) the oldest monkey

3) ape

4) southern monkey

26.Fossil remains of which ancient person were found near Beijing?

1) Pithecanthropus

2) paleoanthropa

3) Sinanthropa

4) Australopithecus

27.How many main races exist today?

1) two

2) three

3) four

4) five

28.Which morphological feature does NOT characterize the Mongoloid race?

1) flattened face shape

2) narrow palpebral fissures

3) noticeable cheekbones

4) straight or wavy soft hair

29.Which human race does NOT exist?

1) Americanoid

2) Caucasian

3) Mongoloid

4) Negroid

30.What did the most ancient and ancient people do during the long period of anthropogenesis?

1) cattle breeding

2) gathering and hunting

3) gardening

4) agriculture

KEY

№1 - 4	№2 - 4	№3 - 3	№4 - 4	№5 - 1	№6 - 3	№7 - 4	№8 - 2	№9 - 4	№10 - 1
№11 - 2	№12 - 1	№13 - 2	№14 - 3	№15 - 4	№16 - 3	№17 - 4	№18 - 2	№19 - 1	№20 - 1
№21 - 2	№22 - 3	№23 - 4	№24 - 1	№25 - 4	№26 - 3	№27 - 2	№28 - 4	№29 - 1	№30 - 2

When preparing the testing, material from the manual Testing and Measuring Materials was used. Biology: 9th grade / comp. I.R.Grigoryan. – M.: VAKO, 2011.

Key questions

What is evolution and what is the proof of its existence?

To us and from whom did man come?

Why did one animal species have to undergo such rapid evolution over the last century?

In 1831, Charles Darwin set off on a voyage on the Beagle as a naturalist. When he set out, he shared the common belief that every existing species is unique and permanent and that worldwide catastrophes destroyed previous populations, the evidence of which was preserved in the form of fossil remains, and new species arose in their place.

Returning from his trip almost five years later, Darwin already had a different opinion. He became convinced that organisms evolve slowly, and that fossils - the ancestors of existing forms - provide partial evidence of this process.

What made Darwin change his idea of ​​the origin of life? During his trip around the world on the Beagle, Darwin collected facts indicating the evolution of species. Of course, these facts were not so numerous compared to the striking and convincing examples that evolutionists have discovered over the past 100 years or more. However, Darwin saw a lot and did a lot based on what he saw, which will be the subject of discussion in this and subsequent chapters.

19.1. Evolution is a change in the heritable phenotypes (inherited manifestations of traits) of individuals in a population

Evolution is a special type of change that can only occur in a group of organisms. An individual does not evolve.

Evolution happens within populations, which can be defined as a group of organisms of the same species living in a more or less limited area.

The process of evolution consists of changing the inherited phenotype, i.e. the external manifestation of the hereditary characteristics of the organism, such as color, size, biochemical composition, speed of development, behavior, etc.

Evolution in a population can occur even if evolutionary changes do not appear in a particular individual. An adult gray butterfly does not become black, just as a bacterium does not become resistant to a drug, but one of the offspring of a gray butterfly may turn out to be black, etc. A population consists of different individuals at different times, and therefore it reflects general changes that have occurred over many years. generations. If a population is examined twice over a long period of time, and if it turns out that during this period new phenotypes have appeared in the population that can be transmitted to future generations, then we can say that evolution has occurred in the population (Fig. 19-1).

19.2. As a rule, information about previous populations exists only in the form of fossil remains.

Because noticeable evolutionary change usually occurs after thousands or millions of years, evolution can be traced by comparing modern populations with ancient ones that are only partially preserved as fossils. We cannot be sure that the fossils we find are typical representatives of their populations, but our knowledge of the fossilization process suggests that they are so. The close correspondence between individual fossils and the populations they represent is clearly demonstrated when a living “fossil”—a living representative of a supposedly extinct fossil group—is discovered.

For example, the lobe-finned fish Latimeria belongs to an ancient subfamily of fish that for a long time we knew about only from the presence of fossil remains. Scientists believed that all species of lobe-finned fish became extinct 75 million years ago. But in 1939, a live cross-finned fish was caught in the waters of the Malagasy Republic at great depths, followed by others.

It is clear from Figure 19-2 that the phenotype of this fish, reconstructed from fossil evidence, is remarkably similar to that of its modern relatives. Examples like these allow scientists to use fossil material with confidence.

For reference

Each element has several varieties called isotopes. Isotopes differ in that their atoms contain different numbers of neutrons. Because the atomic mass of an element is approximately the sum of its protons and neutrons, isotopes of the same element have different atomic masses. To designate isotopes of the same element, their atomic mass (rounded to the nearest whole number) is written to the left and slightly above the element's sign. For example, 14 C is a radioactive isotope of carbon. Other isotopes of carbon are stable (non-radioactive), for example 12 C. Each radioactive isotope of any element is characterized by a certain half-life.

19.3. The age of fossils is most often determined by studying the radioactive substances they contain.

Radioactive substances break apart and are converted into other substances. For example, radioactive uranium decays into lead and helium (a persistent gas), radioactive potassium turns into argon (a persistent gas) and ordinary calcium, radioactive carbon turns into nitrogen, etc.

Some radioactive transformations occur within a few hours, others over several years, and some over eons. Over 456 billion years, only half of a certain amount of 238 U (an isotope of uranium) will turn into lead and helium. The period required for the decay of half a given amount of a substance is called half-life. Each radioactive substance has a certain half-life. If the half-life is known, it can be used to determine the age of rocks and the fossil remains they contain. For example, when the isotope of uranium 238 U weighing 1.0 g decays to 0.5 g in 456 billion years, 0.4 g of lead is formed (the rest of the mass is converted into helium and nuclear energy). After another 456 billion years, only 0.25 g of uranium will remain, but the amount of lead will increase to 0.6 g. To determine the age of a rock, the relative content of uranium and lead in it is measured. The greater the amount of uranium relative to lead, the younger the rock.

The half-life of the uranium isotope 238 U is too long to be used in determining the age of later fossils. The half-life of the uranium isotope 235 U is 713 million years. And the potassium isotope 40 K turns into the argon isotope A, having a half-life of 13 billion years. These half-lives are quite useful for determining the age of many fossils.

Another useful isotope is the 14 C isotope of carbon. It is present along with ordinary carbon in all living organisms in the form of a small but constant fraction of living tissue. Like all radioactive elements, it decays constantly. But while the organism lives, the amount of radioactive carbon in it is replenished as it decays. After the death of the organism, the content of 14 C relative to the total amount of carbon in dead tissues begins to decrease. In fact, in 5570 years there will be half as much left. Therefore, comparing the amount of ordinary carbon with the amount of radioactive carbon allows us to date the most recent fossils, as well as teeth, bones, wood remains and charcoal, dating back 10,000 years.

In general, the "repertoire" of radioactive tests now covers the entire period of life on Earth. Thus, the age of most fossils can now be determined more accurately than ever before.

19.4. To study human evolution, that is, the divergence between hominids (humans) and pongids (apes), it is necessary to consider the differences between them

Since there are people who do not want to admit that the process of evolution involves man, we have chosen him as an example of evolution, although many other organisms could serve as good or even better examples, especially those whose remains are preserved in places where decomposition is under the influence of bacteria was minimal.

The reconstruction of human evolution should begin with a study of the differences between humans and great apes. Knowing them, we will know what to look for to establish common ancestors or "missing links." There are relatively few anatomical differences between apes and humans. The human brain is much larger, and the forehead is higher. The jaws are shorter than those of monkeys, and the face, on which the nose protrudes, is flatter. Human teeth are arranged in the jaws in a gracefully curved arc called the dental arch. In monkeys, the dental arch is whiter rectangular than arched. Some teeth in monkeys are separated by a relatively large distance, while in humans the teeth touch each other. In addition, the canines, or eye teeth, in humans are no longer than the other teeth; in monkeys they are longer and resemble teeth.

Human - bipedal vertically walking creature. The method of movement of monkeys is called brachiation; they throw their bodies from tree to tree, clinging to branches with their hands. Since man is a bipedal creature, he differs from apes in that he has: 1) a wide cup-shaped pelvis; 2) large muscular buttocks; 3) a fairly powerful heel; 4) long kogi; 5) arched foot; 6) S-shaped spine; 7) foramen magnum (a large hole at the base of the skull through which the spinal cord passes), facing downwards, and not backwards, as in monkeys (Fig. 19-3). There are other differences, such as the relative absence of hair and Priapus bone(bones of the penis) in humans.

Since bones are easily fossilized, we can hope that we will be able to fully trace the evolutionary differences in the skeleton of humans and great apes. However, there are significant differences between humans and apes that are not subject to fossilization: human puberty lasts longer (17 years in humans, 8-10 years in monkeys); 2) a person can be left-handed or right-handed; 3) people unite in large groups and use complex means of transmitting thoughts, signs and abstract concepts to each other; 4) humans are able to produce offspring throughout the year, while monkeys reproduce at certain periods/However, there is one, “non-skeletal” difference that is “fossilized” very well. People create tools that shape and reflect their complex culture.

There are more similarities between humans and apes, but not many differences. They have many common anatomical and biochemical features. For example, neither humans nor apes are capable of synthesizing vitamin C and do not have tails.

19.5. Possible common ancestors of modern apes and humans are the extinct arboreal apes that lived approximately 15-30 million years ago

15 million years ago neither modern apes nor humans existed. Fossil remains of ape-like primates have been found, which appear to be their common ancestors. The age of these fossils is approximately 15-30 million years. However, the remains of these ancient fossils are very scarce. Most often this is only a part of the jaw, sometimes just one tooth, less often - finds approaching a complete skeleton. Of greatest interest for our discussion are the fossils belonging to the group Dryopithecus, an arboreal ape (Fig. 19-4), whose remains have been found in Africa, India, and Europe. They are the likely ancestors of great apes such as the gorilla and chimpanzee, and appear to be closely related to human ancestors.

The pelvis of Dryopithecus was adapted for walking on four legs, but its size was smaller than that of modern chimpanzees and gorillas. Their legs were not as long as those of humans, and their arms were shorter than those of chimpanzees or orangutans. Some Dryopithecus have canines (eye teeth) larger than those of humans, but smaller than those of modern apes. Human canine roots are larger than seems necessary. This suggests that our ancestors had larger fangs. There are also similarities between the molars of humans and Dryopithecus.

The dentition of Dryopithecus varies, as they belonged to several different families, genera and species. Most dryopithecines had teeth similar to those of monkeys, but some are also known that had a more rounded dental arch, relatively small fangs and other features similar to human teeth. Elwyn Simons united humanoid forms under a common name Ramaptihecus punjabicus.

These fossils lived in Africa and India, and possibly in areas in between. They lived about 14 million years ago, as determined by potassium-to-argon dating done at the site where one was discovered by the late Lewis Leakey.

Leakey and Simone disagreed about the names of some ape-like fossils, but they shared the same interpretation of their origin, namely that 12-14 million years ago, animals that showed signs of developing the ape-like features that we see in modern pongids lived in warmer climes Old World.

Together with them there was a group of primates very similar in appearance, whose teeth had a clear resemblance to human teeth. (Simonet called them Ramapithecus.) Leakey formally separated these humanoid-jawed individuals from the Dryopithecus group and classified them as hominids.

Extremely important information was obtained from the discovery of the remains of a fossil Ramapithecus, known as the Calcutta jaw. They show that the period of maturation of Ramapithecus, in contrast to Pongida, was very long, just like in humans. The lower jaw contains all three molars, but with very different wear. The first is heavily worn, the second is only moderately worn, the third is almost completely unworn. This differential wear of molars is observed in humans and fossil humans (including Australopithecus), but is never observed in apes. According to Simons, the third molar, or wisdom tooth, is a sign of maturity in all humans and apes. It appears after the development of the skeleton and puberty of the body are completed. In apes, which have a short period of maturation, the molars appear quickly one after another and therefore they are almost equal in the degree of wear. In humans, the first molar erupts at approximately the same chronological age as in monkeys, but the second appears somewhat later, and the third much later than in monkeys. Therefore, in a person who has reached maturity, the third molar is completely new, and the first is worn out, which is also characteristic of the fossil Ramapithecus.

If all this is confirmed by further findings, the picture of human evolution will appear as follows:

1) The first apes evolved from Old World monkeys that gradually lost their tails. These apes then diverged into forms that appear to be the ancestors of Dryopithecus and Gibbons (Gibbons are a separate family of Apes). 2) 15-20 million years ago, Dryopithecus diverged into a) forms from which humans would later emerge ( Ramapithecus), and b) the forms from which modern pongids will arise ( Dryopithecus).

19.6. A closer ancestor to humans appears to have been Australopithecus.

About 2, and perhaps even 3 or 4 million years ago, hominids not only existed, but their anatomy was very similar to that of humans. Even their heads had a number of features characteristic of humans. The teeth were almost the same as those of humans, with the exception of the molars, which were larger in size, and the jaws were somewhat smaller than those of Dryopithecus.

R. A. Dart, the first to discover these hominids, did not immediately mistake the small skull he found for a hominid skull, although he drew attention to the fact that the teeth and jaws had many features characteristic of hominids (Fig. 19- 5, B, C). So he called his find Australopithecus africanm.

In 1936, ten years after Dart's discovery, Robert B. Broom discovered the pelvic bones of an Australopithecus (Fig. 19-5, A). Apart from minor details, their shape clearly resembled the familiar shape of human bones, proving that Australopithecus walked upright.

This was not entirely unexpected, since the foramen magnum of the fossil found by Dart was directed downwards, which also indicated an upright position of the body. Additionally, many other anatomical details of the skeleton indicated that Australopithecus was more of a mini-brained human than anything else.

In the late 1950s, Lewis Leakey's wife, Dr Mary Leakey, discovered the most astonishing of all finds: the skeletal remains of an Australopithecus, along with stone tools of the earliest known type.

Based on the radioactive decay of potassium, it was established that the age of the remains is 1.75 million years, i.e. this proved that A. africanm created tools.

19.7. Gradually A. africanus evolved into a form called A. habilis, which in turn gave rise to Homo erectus about a million years ago

Although the Leakeys have produced the largest number of finds tracing the transformation of Australopithecus africanus into Homo erectus in Tanzania (partly aided by the Tanzanian climate), Homo erectus was first discovered by the Danish physician Eugene Dubois in Java in 1891.

Du Bois suggested that Java was the place to look for the "missing link." Having gone there, he found what he was looking for! The species he discovered is now found in most tropical and temperate zones of the Old World. However, his luck remains amazing to this day. For 40 years, other expeditions tried unsuccessfully to repeat his discovery.

At first, Dubois's find was called Pithecanthropus erectus(upright ape-man), but now this species has received the name Homo erectus(upright person).

Anatomical changes in Homo erectus observed mainly in the skull.

The size of his brain approached the size of the brain of a modern person. And some representatives of H. erectus had the same brain as some modern H. sapiens with a small brain volume.

Speaking about the volume of the human brain, it should be noted that the most famous H. sapiens with a small skull size was the French writer Anatole France, whose skull volume was only 1017 cm 3 with an average volume of 1350 cm 3. Thus, this does not mean that H. erectus was a weak-minded creature. The tools he made testify to his extraordinary abilities and technical skill.

H. erectus appears to have had other behavioral similarities to modern humans: several H. erectus skulls have been found carefully opened, as if their contents had been eaten during a cannibal feast or ritual.

19.8. The increase in the volume of the human brain over the past 2 million years is one of the most rapid evolutionary changes

Now there is a whole series of fossil skulls found that allow us to carefully trace the path from A. africanus with a mini-brain to H. sapiens. Although brain growth occurred in relatively small steps, it represents one of the most rapid evolutionary changes in the history of life on Earth. In less than 2 million years, the average volume of the hominid brain more than doubled. This is an exceptional speed compared to the normal rate of evolution. For example, the evolution of the horse from its dog-sized ancestors to its modern form took place over 60 million years.

The volume of the human brain is no longer increasing, and the pH appears to have remained that way for almost 250,000 years. In fact, N. sapiens neanderthalensis(Neanderthal man, a race of our species that “flourished” during the last ice age) the brain volume was on average 100 cm 3 larger than that of modern humans. It is likely that the brain is no longer enlarging because the already large size of the newborn's head barely allows it to fit through the mother's pelvis, which must expand slightly during labor to allow the baby to be born. But perhaps there were other, even more important reasons.

19.9. The evolution of Homo erectus into Homo sapiens ended about 300,000 years ago

Paleontologists believe that N. erectus evolved into Homo sapiens about 300,000 years ago, but they admit that this figure is somewhat arbitrary. The evolution of human anatomy, behavior and physiology, that is, the human phenotype, is a gradual process. It continues to this day.

19.10. There is actual evidence of the evolution of one butterfly species within the last 100 years or more

The first documented observation of evolution concerned butterflies, which developed black coloration as the forest environment in which they lived became more complete.

Even in Darwin's youth, almost all British Biston betularia butterflies were mottled, pale gray and white. A black form of Biston betularia also existed, but was rare. We know this because it was highly sought after by collectors. And now the forests of Birmingham in England are full of them, and they are as common as they once were rare. Evolution has occurred in our time.

Modern biologists noticed that the black form was common in areas east of large industrial centers such as Birmingham, and, knowing that in England the winds usually blow from west to east, they suggested that the smoke and soot from factories and factories somehow influenced the formation of the black form. British biologist

H. B. D. Kettlewell noticed that in forests where there were black butterflies, the trees were black and sooty, and in forests where there were still many gray and white spotted butterflies, the old "typical form ", - relatively clean. The trunks in these forests were covered with variegated gray-white lichen. He found that the black color in butterflies is associated with natural pigmentation and is inherited, like the typical spotted form.

Kettlewell suggested that since birds are the most dangerous enemies of butterflies, the more visible a butterfly was sitting on a tree trunk, the more likely it was to be seen and eaten. Therefore, the spotted butterfly was relatively safe on a trunk covered with lichen, and the black butterfly on a trunk covered with soot (Fig. 19-6). To test his hypothesis, Kettlewell bred butterflies of both forms and released them into clean and smoky forests. Before releasing them, he painted a dot under the wing of each butterfly. Kettlewell released 799 butterflies into lichen-covered forests and after 11 days captured 73 butterflies with his mark.

Spotted butterflies were more likely to survive among lichen-covered trees. Over an 11-day period, each spotted butterfly was approximately 2.9 times more likely to persist than a black butterfly.

In smoky forests, the black form of butterflies had an advantage. Here the experiment was carried out 2 times. In 1953, 27.5% of black butterflies were caught in 11 days, but only 13% of spotted ones. During this period, the survival rate of black butterflies was 2.1 times higher than that of spotted butterflies. In 1955, the survival rate of black butterflies was again 2.1 times higher.

Kettlewell used filming to record the actions of birds given the opportunity to catch one of two species of butterfly sitting in a tree in front of them. In Birmingham, birds were much less likely to spot black butterflies. For example, redstarts ate 43 spotted and only 15 black butterflies in two days. In clean forests it was the other way around. The gray flycatcher ate 81 black butterflies and 9 spotted ones. Filming showed that it was not easy for birds to see spotted butterflies against a spotted background of lichen and black butterflies against a dark background of soot. Not surprisingly, in the smoky environment, about 100 species of butterflies began to take on dark colors.

There are other cases of observable evolution known to science, many of which are caused by our radical interventions in nature. One of them is the acquisition of resistance to DDT by mosquitoes. Another case is the acquisition of antibiotic resistance by infectious bacteria. These examples, as well as fossil evidence, confirm the fact of evolution. Thus we arrive at the next question: what causes biological evolution?