The origin and evolution of human
Until a little more than a century ago no one thought that man could also have originated from a slow and gradual evolution, because everyone believed that man was a special creature, created by God in his image and likeness and therefore profoundly different from all other living beings. So it is written in the Bible and so it was taught to the people.
It was Charles Darwin, in 1871, who was the first to affirm, in his book "The origin of species", that we too are living beings like everyone else, and that therefore we are subject to the same laws that govern natural phenomena. Man, therefore, must have had ancestors who, in turn, must have possessed characteristics similar to those of the animals he most resembles today, namely apes. Hence the false belief that Darwin said that man is descended from apes.
In reality, man cannot derive from an animal that is contemporary to him, just as one of us cannot be the son of his own cousin. Darwin simply stated that man and ape must have had common ancestors in the not too distant time, just as two cousins have grandparents or great-grandparents in common. Going far back in time, we would arrive at those few primordial organisms that were the ancestors of all living forms currently present on Earth.
1. THE THEORY OF EVOLUTION
Before going into the subject, perhaps it is appropriate to clarify what scientists mean when they speak of "theories", and in particular to see what Darwin's theory of evolution says.
Failing in a coherent and logical way to justify the enormous variety of living organisms, man did not know how to do better, in the past, than to resort to the concept of creation. According to this point of view there would have been a god, or a transcendent entity with infinite possibilities, who would have populated the Earth with all sorts of living beings and assigned man a pre-eminent role. As everyone knows, there is no single myth of creation: each culture has developed its own, exclusive and original in detail. All these myths, however, by their very nature, are not scientific theories. They are not scientific theories not only because it is not possible to make predictions from them, but also because they cannot be refuted: that is, it is not possible to prove in any way either that they are true or that they are false. All these myths, in other words, lack the typical prerogatives of scientific theories: they are acts of faith and as such do not have nor, in truth, do they claim to have a rationale.
Being an act of faith, it is not possible, for example, to convince a believer of the inconsistency of the biblical myth of creation, nor is it the intention of scientists to do so: everyone is free to believe what he wants. At the same time, however, the scientific community claims that those who appreciate the logic and rigor of the scientific method, that is, the search for truth through observation and experimentation, be free from anathemas and impositions of any kind.
Creationists often, with the intent of belittling Darwin's theory of evolution, say that it is basically "just a theory" and therefore it is absurd to claim that truth can spring from it. Those who speak in these terms do not know what a scientific theory is. So let's try to explain it in a few words.
A scientific theory is nothing more than a hypothesis, that is, an idea that is formed in the mind of man, after he has carefully and scrupulously observed natural phenomena and laboratory experiments. It is therefore not reality but a conjecture, through which it is possible to justify natural phenomena in a logical and coherent way. A good theory must not only account for the phenomena from which it itself originated, but must also be able to foresee new ones to be verified in the future.
Furthermore, a theory is not something fixed and immutable, valid once and for all, but a conceptual tool to be continuously tested. A theory is definitively abandoned when it is no longer able to explain the observed facts in a clear and coherent way. Normally, however, when a theory, following the interpretation of some new phenomenon, contradicts the concepts it expresses, rather than definitively discarded, it is appropriately corrected and modified. A scientific theory if it is "just a theory", as the creationists say, is simply all it needs to be.
Darwin's theory of evolution, like all great theories, is very simple and is based on three fundamental assumptions:
- First: living organisms, be they animals or plants, have many children: many more than they would need to remain in stable equilibrium with food and with the space that the environment makes available to them.
- Second: organisms of the same species are not all identical to each other; there are bigger and smaller ones, slower and faster ones, lighter and darker ones, and so on.
- Third: there is a constant struggle for survival between organisms of different species, and also between organisms of the same species. In this struggle, the strongest individuals prevail, i.e. those best equipped to access the resources that nature makes available to them.
At this point, let's go back to the evolutionary history of man.
2. THE FIRST FINDINGS OF HUMAN FOSSILS
Before Darwin, in 1856, published his book on the theory of the origin of species by natural selection, fossils of a skull and some limb bones belonging to a being were found in the Neander River valley near Düsseldorf, Germany. Certainly human, but with very particular structural characteristics.
Obviously, that find was not interpreted on an evolutionary basis and indeed some eminent biologists of the time believed it could be the remains of a modern man, deformed or seriously ill. The German pathologist Rudolf Virchow went so far as to specify that the individual must have suffered from rickets at a young age, aggravated by arthritis in old age (as evidenced by the arched bones of the limbs) and further worsened by some bad blow received in the head in adult age. For others, however, it was a Cossack soldier of the Russian army (the arched legs were evidence of a life spent on horseback) who had participated in the war against Napoleon in 1814 and who, exhausted from fatigue (the prominent supraorbital arches were the result of continuous frowning in pain) had taken refuge in a cave where had met his death. Later, however, Thomas Henry Huxley, Darwin's close friend, correctly interpreted it as the vestiges of a primitive human race. This race, of which many other specimens will later be found, will be given the name of "Neanderthal Man" (Homo neanderthalensis).
The Neanderthal man must have been a stocky individual, about a meter and a half tall, with a skull of abnormal thickness, long and narrow, but with a considerable capacity (over 1,500 cm³), even higher than the average of the present man; it also had a receding forehead, very prominent supraorbital arches and the foramen magnum not perfectly parallel to the ground. All these characteristics led to imagine the Neanderthals as beings with the appearance of brutes who inhabited the caves and who proceeded with a forward curved gait, similar to that of the current anthropomorphic apes.
Today we know instead that Neanderthal man was not at all a bestial being, but that he had an intelligence and carried out an activity very similar to ours (for example he knew fire and buried the dead, demonstrating that he had respect for the dead). He lived in a very recent era (from 130,000 to 35,000 years ago) and is currently considered a subspecies of Homo sapiens which has been given the scientific name of "Homo sapiens neanderthalensis", while we are "Homo sapiens sapiens". He is therefore not our ancestor, but rather a species of man who had an evolutionary path that diverged from ours, an evolutionary path that led to extinction. Our true ancestors instead inhabited Africa at least 3,5 million years ago.
As we have seen, with Darwin the scientific community became aware that man, like any other living species, must have had its own evolutionary history and set out in search of traces of its origin. In this way, paleoanthropology was born, that is the science that deals with the research and cataloging of the fossil finds of mankind. Among the human fossils are included, in addition to bones, also the tools that man himself made and used, and the traces of his activity, such as the remains of the fires that he lit to warm up and keep away the ferocious animals, and the paintings he created on the walls of the caves where he lived.
All the fossil finds concerning the human species have been found practically in the last century and come mainly from Africa, but some important finds have also been found in Asia and Europe. The fossil found up to today, are not many and could find complete accommodation in a conference room: however they have proved sufficient to reconstruct, in a satisfactory way, the evolutionary history of man.
The discoveries of the last twenty years have put back in time the date of the origin of our species, which previously was around 500,000 years. These latest findings have also made it conclusively clear that mankind had its origins in Africa and not in Europe, as had long been believed. In reality, the belief that Europe had been the cradle of humanity had no scientific basis, but was based exclusively on the presumption that European civilization was the most advanced of all. For this reason, remains of hominids, found in Java and in China at the end of the last century and at the beginning of this one, were interpreted as remains of monkeys and not as our real ancestors.
The term Hominid today collectively indicates all the ancestral types of the human species characterized by an upright gait. The only hominid species that will eventually survive natural selection will be ours, what we have called Homo sapiens sapiens.
3. THE MOST RECENT DISCOVERIES
Two million years ago two different types of hominids lived simultaneously in Africa: the Australopithecus and those of the genus Homo. The Australopithecines, whose term literally means "southern apes" (ie southern monkeys), were actually not apes, but primitive men who became extinct without leaving descendants. The others, the hominids of the genus Homo, are our most direct ancestors and have evolved to reach our species.
The most sensational discoveries of recent years are represented by the very famous Lucy and by the traces of the footsteps that three individuals left on the still hot ash of an African volcano more than three and a half million years ago. In both cases, we are talking about Australopithecus that lived in the savannah and that had already acquired an excellent adaptation to the upright gait.
Lucy was discovered by a Franco-American expedition led by paleoanthropologists Yves Coppens and Donald C. Johanson, in 1974. Together with crocodile, rodent and elephant bones, they were found in the Afar desert valley in Ethiopia, about sixty kilometers away. from Addis Ababa, some bones of hominids which were later recognized as belonging to a single individual. That individual was a young female who lived over three million years ago. From the structure of the skeleton (40% complete), one could easily deduce that it was able to walk upright. Lucy's name was inspired by a Beatles song very popular at the time: "Lucy in the Sky with Diamonds" (used, among other things, also as a cryptogram of the hallucinogenic substance LSD) that researchers frequently listened to on the radio during excavation operations.
The footprints of three hominids were found in 1976, on a layer of fossilized volcanic ash, by a scientific expedition led by the famous paleoanthropologist Mary Leakey, wife of the even more famous Louis Leakey, founder of a family of researchers who for over fifty years operates in East Africa in the so-called Rift Valley. Louis Leakey, now a legendary figure in the field of paleoanthropology, was born in Kenya in 1903 from an English pastor who moved to those lands to fulfill his spiritual mission; the scientist's death occurred in African region in 1972.
Near Laetoli in Tanzania there is a volcano, now extinct, but which a few million years ago was active and erupted lava together with a large quantity of ashes and lapilli. On this dusty material, wet from the rain, three hominids left their footprints, walking on two legs like us and whose feet were not very different in shape from ours. The soil on which the traces of the three individuals were preserved was dated with the potassium-40 method and turned out to have an age of 3.7 million years.
One year after Lucy was found, the expedition led by Donald Johanson made another sensational discovery. On the eroded side of a hill were the remains of a group of individuals who most likely died together following a natural catastrophe, perhaps a flood. Hundreds of teeth and bone fragments were recovered, belonging to at least thirteen individuals (including four children) that someone piously baptized "First family". They were specimens with characteristics similar to those of Lucy. All these hominids were eventually given the scientific name of Australopithecus afarensis (from Afar, the Ethiopian desert where Lucy was found).
4. THE UPRIGHT STATION OF MAN
The most singular and in a certain sense the most surprising characteristic of man is the position that his body assumes. Our species is the only one of all mammals to walk upright. The conquest of the station and upright walking, from an evolutionary point of view, experts say, is difficult to acquire and is much more unlikely than the development of the brain itself.
It was once believed that standing, brain development, and the use of tools had been acquired by primitive man at the same time; today, however, paleoanthropologists think differently. For example Owen Lovejoy, a biologist expert in animal locomotion, is convinced that the hominids acquired the erect position when they still lived in the forest and that then this particular position of the body proved to be advantageous when they were forced to live in the savannah. But what pushed the evolution of hominids in this direction? What evolutionary advantages may having permanently walking on only two limbs, compared to walking on all fours typical of all other mammals?
As everyone (or almost everyone) knows, evolution takes place through small random variations of the DNA structure which are called mutations and which are reflected in as many slight modifications of the organism within which this DNA is contained. Mutations, in themselves, are neither advantageous nor disadvantageous for the individual who undergoes them: it all depends on the way in which this individual will react to the test of the environment. In other words, the environment will consolidate or cancel the variations that appear on the changed individual.
The four-limb gait is undoubtedly more comfortable than the bipedal one and it is also the one that requires less energy expenditure. The acquisition of the bipedal gait must therefore be interpreted as an extraordinary event and not at all convenient. The upright position in fact requires a radical restructuring of our anatomy, compared to which the remarkable development of the brain represents a phenomenon of secondary importance.
We often speak of evolution in finalistic terms, as if a particular change on an organism were made with the aim of achieving a certain goal. It is said, for example, that man has acquired the erect position to be able to see in the distance over the tall grasses of the savannah; but that cannot be true.
The mutations of the DNA and the changes that, consequently, these mutations produce on the organism, cannot take place in anticipation of an environment in which these organisms do not yet live: natural selection has neither conscience nor foresight. The acquisition of the upright position by primitive man did not happen to allow him to see better in the distance, but to guarantee him the maintenance of the traditional way of life in an environment that was changing, that is, in the forest in which that organism still stood.
Nature, as we have said, cannot predict the environments that are yet to come and species cannot pre-adapt themselves to an environment that does not exist and that who knows if ever there will be. The possibility of seeing better in the distance, for the Hominid who had acquired the standing position, was therefore not the cause of the innovation, but rather the effect of its existence.
To conclude, since evolution has neither purpose nor direction, we must believe that the acquisition of the standing position by primitive monkeys that inhabited the forest happened by chance and placed those animals in more favorable conditions than the others, because it allowed them to maintain the traditional way of life in a changing environment. We will return to the subject.
5. THE NEOTENY
Today it is believed that man is basically the result of a biological phenomenon that takes the name of neoteny. This term, which etymologically means "prolongation of youth", indicates the tendency of living species to retain some embryonic physical characteristics in adulthood.
A curious-looking animal lives in Mexico: its name is axolotl. It resembles a giant tadpole but unlike the tadpole, which is an immature frog and therefore cannot reproduce, the axolotl is able to do so. That is, it is a being immature in appearance, but adult in function.
This strange animal has been studied in the laboratory and it has been discovered that, by adding a minimum amount of iodine to the water in which it lives, it turns into a salamander. Iodine is the essential constituent of the hormone that produces metamorphosis: if iodine is lacking in the lakes where the salamander lays its eggs, the tadpoles that are born cannot become adults and die. The axolotl, on the other hand, is both able to transform itself into a salamander if the waters in which it lives are rich in iodine, and to remain in an embryonic state and continue to reproduce in the form of a tadpole, if the waters are free of iodine.
A sudden and fortuitous mutation must have determined, in very distant times, the appearance, on some tadpoles of the Mexican salamanders, of mature sexual organs and therefore capable of producing spermatozoa and eggs. These tadpoles would therefore have found themselves in the conditions of being able to reproduce before the metamorphosis had taken place: in this way the axolotl must have been born. But what does the strange mutation of the axolotl have to do with the history of human evolution?
The relevance indeed exists because many scientists believe that man too is a neotenic product. Indeed, not only man, but the whole group of the most evolved animals, namely the chordates, could be the result of a neotenic mutation that took place hundreds of millions of years ago. Chordates are a type (or philum) of animals, to which vertebrates belong, provided with a dorsal cartilage cord that acts as a propulsive and support organ. Now, the fact that there is no invertebrate that resembles the chordates to the point of being able to be candidates for its ancestor, excludes that the chordates can be derived from a mutation that appeared on some adult individual. Conversely, the larva of the sea urchin, an animal that has nothing in common with the chordates, resembles this group of animals to such an extent that many believe that the chordates have evolved precisely starting from the immature structure of the sea urchin which, like the axolotl, following a mutation, it found itself in a position to reproduce by virtue of neoteny.
Even adult men, we said, have many neotenic characteristics. If we observe the fetus of any mammal, for example the pig, we note that the head is very developed compared to the rest of the body: this disproportion, however, decreases later in the course of development. In the case of man, however, the reduction in the size ratio of the head / body size is smaller. Our head, in other words, retains considerable dimensions even in adulthood, allowing the production of a large brain mass.
But this is not the only neotenic feature that we carry around. The hairless body, for example, is an embryonic feature of mammals which, as adults, all have their bodies covered with hair. Even the thin and delicate skin, brittle bones and small teeth of adult humans must be considered embryonic characteristics of mammals.
6. BIPEDAL GAIT AND FAMILY RELATIONS
Now, referring to the bipedal gait, it has been observed that it requires an enlargement of the lower limbs and a considerable development of the muscles. However, a child's legs are small and frail: the bipedal gait should therefore not be the result of a neotenic modification. Modifications that are not neotenic in nature are to be considered unnatural and therefore more difficult to acquire.
We have said that the standing position is not at all a natural position (and much less comfortable) as one might superficially believe: it is a challenge to the laws of gravity because it raises the center of gravity of the body and places it in a position of perennial instability. The upright position therefore requires, on the part of the individual who possesses it, a considerable energy expenditure for the continuous search for the equilibrium position. In addition, it also implies a series of risks such as immobility, or almost immobility, in the event of injuries or fractures of a limb and a series of disorders, even serious, such as crushing of the vertebrae, sciatic veins, varicose veins, etc. So what would have been the benefits deriving from this mutation able to compensate for the physiological inconveniences that must have tormented primitive man and which still afflict modern man today?
The real benefit, according to the American anatomist O. Lovejoy, already mentioned above, would be represented by the possibility of using the upper limbs as tools for gripping and transporting objects of various kinds and at the same time to acquire, thanks to the greater height, better control of the territory. Lovejoy has elaborated a theory that would explain the best adaptation to the environment that the upright position would have represented for the progenitors of the human species when they found themselves in the savannah having to compete with the more prolific apes.
It is known that living organisms are all the more successful in the struggle for survival the more they are able to leave offspring: It would therefore not be a question of producing a large number of children, but rather of ensuring that as many as possible of those born remain alive and for the time necessary for other offspring to generate new childs. Well, man, unlike all other mammals, and therefore also monkeys, does not have inspiration. This term indicates that period of fecundity in which animals manifest, through evident external signs, an irrepressible desire for mating. Everyone has been able to observe dogs and cats in the period of estrus, that is when, as they say, they are "in heat".
The estrus is a guarantee of prolificacy as any mating that occurs in the period of time established by nature would inevitably end with the fertilization of the eggs and therefore with the birth of one or more children. But in man it is not like that: man, as everyone knows, can have sexual relations without these necessarily leading to the birth of a child.
What does all this have to do with standing? Lovejoy imagines that among the hominids that inhabited the forest some acquired the upright position through a mutation, after they were forced to descend from trees induced, as we shall see later, by a need dictated by climate change. In these individuals, as soon as they landed, the upright posture was presumably very unsafe, but it slowly improved. Some mutations contributed to this evolution, including, according to Lovejoy, the appearance of an individual lacking inspiration.
The first female without the estrus would therefore not have presented those changes in behavior, typical of animals "in heat", capable of attracting the attention of the dominant male who is the one who, within the group, fertilizes all the females. This behavior is very common among mammals and is the rule, for example, among gorillas and baboons. The other males of the group are generally precluded from mating, even if, in reality, some of them are allowed to do so but only in infertile periods. Thus it has been observed for example among baboons.
The fact of not possessing inspiration should represent an evolutionary disadvantage: evolutionary theory teaches, however, that a character can appear disadvantageous if considered in its own right, but advantageous if evaluated together with others with which it interacts. Let's imagine then that within a group of pre-hominids who inhabited the forest and who lived in trees, but who were also able to walk on the ground in an upright position (or almost), a female without estrus appeared. This female could have mated with a young member of the group without encountering obstacles from the dominant male as the latter would not have noticed her precisely because he lacked her inspiration. From these apparently sterile relationships, an offspring could have been born, and therefore other females of that type.
A female, however, who had found herself alone to provide for the rearing of the little one, would have encountered enormous difficulties and perhaps would not have made it possible for her son and herself to survive. Previously, within the group, there had been no such problems, because, as currently happens in animals living in communities, all members of the group were called to collaborate for the common interest.
Because of the situation that had arisen, a new type of relationship had to develop between the individual members of the group; that is, a personalized monogamous bond had to be established between individuals of different sexes, in which the male, perhaps psychologically blackmailed through previously unknown emotional calls, would be linked to a single female, and precisely to the one from which he had had the son. Perhaps in this way what we call "love" was born, that is, a stable couple relationship based on attractions of a different type from those stereotyped behaviors found in animals that lead community life.
In this particular situation, the upright position would have been of great use because it would have allowed the male, while the female was taking care of the young, to go in search of food and to carry it, using the upper limbs, to their children and their mother. The liberation of the hands from the slavery of locomotion would have allowed the transport of food and therefore bipedalism and the upright posture would have proved, in the end, an advantage in the struggle for existence, because they would have allowed the improvement of parental care and therefore ultimately a better guarantee of survival.
7. THE DEVELOPMENT OF THE BRAIN
The development of the human brain or, better said, such a high weight ratio between brain mass and body mass, is a fact of secondary importance and easier to acquire than the standing position as, as we have said, it is linked to neoteny. The human brain is of considerable size only when compared to those of the body. The elephant brain, for example, is undoubtedly larger than ours, but the weight of the animal is also considerable, therefore, after all, the weight of the brain / body weight ratio, also in this case, is definitely a favor of man.
The brain serves to control and coordinate the movements of the various organs. There are receptors scattered here and there on the body of animals, which pick up signals from the outside world and send them to the brain: this, in turn, after analyzing them, prepares the appropriate responses to be transmitted to the muscles and glands arranged in the different parts of the body. The human brain is not only in sufficient quantity to carry out these functions, but there is still more to carry out other activities such as, for example, those connected with logical thought or with the affective and psychic sphere.
However, the greatest potential of the human brain lies not only in quantity (human brain mass is more than double, for example, that of anthropomorphic apes), but also in quality. In other words, the human brain is more developed especially in some areas such as in correspondence with the temporal lobes which are the part that controls speech and the frontal lobes which are the seat of logical thought.
This unbalanced development of the brain has allowed man to communicate with his fellows, but above all to plan for the future. Man, in fact, is the only animal capable of predicting what consequences a certain action will lead to. This makes programming feasible, that is the possibility, for example, of building tools that are not immediately used, but which could be useful in the future. The articulated language must then have represented the fundamental tool for this activity as it would have allowed the projects to be coordinated together with the other members of the group.
8. THE FOOD REGIME
Finally, man is distinguished from the anthropomorphic apes, that is, from the animals that most resemble him, also for the diet. While monkeys feed on fruits, leaves and berries, humans also eat meat. The diet is closely linked to the characteristics of the digestive system and in particular to the teeth. Human teeth are all more or less the same size and arranged on a parabolic tooth arch. The teeth of anthropomorphic monkeys are instead of larger dimensions (especially the canines) and the dental arch has the shape of a U, that is, with canines, premolars and molars arranged in two parallel rows. In addition, the diastema is still present in apes, a space between incisors and canines that allows the interlocking of the dental arches. In humans, this space does not exist precisely because the teeth, and especially the canines, have reduced in size.
If we now go to see the characteristics of the teeth of the hominids of the past we note that in the Australopithecines the diastema has gradually reduced without ever completely disappearing, while no hominid of the genus Homo presents the diastema. This testifies to the fact that our direct ancestors had a more varied diet than that of the Australopithecines, with whom, for a long time, they coexisted.
The teeth, however, in addition to eating, also serve as a defense; if the canines of our ancestors, for example, had shrunk in size before they had learned to make tools for fighting, they would have found themselves deprived of a valid defense aid and most likely would have become extinct.
9. THE EVOLUTION OF HOMINIDS
Let us now return to the evolution of the hominids. The most ancient hominid that has been found fossil up to now is Australopithecus afarensis: it appeared almost 4 million years ago and its remains allow us to reconstruct its appearance.
Australopithecus afarensis was an individual of short stature, stocky and with a marked sexual dimorphism: that is, the females were much smaller than the males. In the human species the difference in height between males and females is not so evident, while it is still found in gorillas. However, this is not the only ape-like character present in this ancient hominid: the face had a prominent muzzle, typical of animals, and the brain (400 cc) was no larger than that of a current chimpanzee. The position of the body, on the other hand, was decidedly erect. It is undeniable, therefore, that the Australopithecus of Afar had a human body and an ape head, but in reality it was different from both modern man and current anthropomorphic apes.
The dentition of these hominids presents the diastema, as is currently known in the anthropomorphic monkeys, while the molars, contrary to that found in the more evolved monkeys, are more voluminous than the anterior teeth (incisors and canines). This observation suggests that the diet of the Afar Australopithecus consisted of hard products, such as nuts and grains, which need to be chewed for a long time before being swallowed. Here is further proof that Australopithecus no longer lived in the forest, where chimpanzees and gorillas still live and where soft fruits and vegetables are eaten, but in the savannah where harder foods are found.
The reason why primitive man would have moved away from the forest to go and live in the savannah today is explained by resorting to a series of natural events that would have occurred between the end of the Miocene and the beginning of the Pliocene, i.e. approximately between 6 and 4 million years ago. The events we are talking about would in turn be the consequence of a geological phenomenon of larger proportions which involved the entire earth's surface and which takes the name of "continental drift".
Two hundred million years ago, at the beginning of the Mesozoic, the emerged lands were all gathered together in a single continent that geologists call Pangea. The Pangea subsequently broke into two blocks, one in the north called "continent of Laurasia" and one in the south called "continent of Gondwana". Between the two continental blocks a sea of enormous dimensions called Tethys or Mesogean sea crept. Subsequently, the two great continents also broke up into smaller "clods" which drifted away, traveling on the fluid mantle below. These continental blocks then collided with each other (and still do so today), causing seismic and volcanic phenomena as well as the overlapping of their edges with the formation of mountain ranges. As a result of these clashes, some clods fractured further.
In its slow and persistent movement northwards, the "African plate" ended up colliding with the European one. Following the collision, the great primordial ocean of the Tethys closed, leaving small scars represented by the Mediterranean, the Black Sea and the Caspian. Subsequently, the Mediterranean dried up, most likely due to strong evaporation and the simultaneous temporary closure of the Strait of Gibraltar, which prevented the supply of Atlantic waters. The area of the Mediterranean basin then turned into a great desert, interrupted here and there by salt lakes, and the climate of the whole region changed radically. From northern Europe to northern Africa, the climate became colder and above all much drier. At that point, the equatorial forest, which previously extended over a vast territory, began to retreat, leaving space for the formation of immense savannas.
East Africa, which in the meantime had separated from the rest of the continent, due to the formation of a deep tectonic fracture called the Rift Valley, also rose and changed its climate significantly. Plants and animals that failed to adapt to the new environmental conditions disappeared while other organisms, coming from neighboring areas, found a habitat suitable for their lifestyle. The fauna and flora in that area therefore changed profoundly.
In those parts also lived our most distant ancestors who in the meantime the Rift fault had separated into two groups: those who remained in the west, where the equatorial forest environment persisted, would then have differentiated into the current anthropomorphic apes, while those who found to the east, in a savannah environment, they gave rise to the Australopithecus, that is, to that group of organisms that would have definitively separated from the animal world. This hypothesis was jokingly called by the French paleoanthropologist Yves Coppens "East Side Story". According to Coppens, therefore, it was not the hominid who came out of the forest to head towards the savannah, but it was rather the forest itself that disappeared under his feet.
The case of East Africa that we have just described is an instructive example of what is called "speciation" in biology, that is, the emergence of new species. The new species, as we have said, are produced by mutations and yet these alone are not enough: environmental pressure also plays an important role. If mutations occur in an environment that always remains the same, these mutations will not have followed resulting either insignificant or even lethal and thus will leave the organisms, as a whole, as they always have been. On the other hand, the situation of an organism that finds itself living in a new environment would be different: in this case the mutation could acquire a positive and lasting meaning.
The Platyrrine monkeys of the New World, for example, well adapted to living in trees, have not changed shape for millions of years, despite the occurrence of countless mutations which, however, the environment has regularly canceled because they proved unsuitable in a territory that always remained. the same. The pre-hominids, on the other hand, who found themselves living in the savannah, that is, in a completely different environment from that in which they lived before, have undergone mutations regarding posture, the development of muscle masses, the shape and size of the teeth and jaws, which turned out to be as many characters of fundamental importance for the new environment.
10. THE OTHER AUSTRALOPITHECES
Australopithecus afarensis is not the only species of australopithecus that has been found fossil. Another specimen of the same genus, but a little more evolved, was found in South Africa as far back as 1924.
In the locality of Taung (the place of Tau , the Lion) on the southwestern border of the Transvaal, in the spring of 1924, some stonemasons extracted from the rocks a skull, in good condition, which was delivered to the director of the mine who, ignoring the scientific value, he used it as a paperweight until a young student, who had noticed it, advised the manager to take it to an anatomy professor at the University of Johannesburg, certainly Raymond Arthur Dart.
He observed that the skull had some typically human characteristics such as rather small teeth and the position of the foramen moved forward, while other features, such as facial bones and small brain size, were specific to monkeys. Dart also noted the presence of many milk teeth which suggested that the skull must have belonged to a very young individual, perhaps a 5 or 6 year old child. Given its young age, the fossil was given the provisional name of "Taung Baby" (Child of Taung), and with this name it is still known today.
The typically human characteristics of the skull were represented, as we have said, by the shape of the jaw and by the teeth (in particular the canines) of rather small size and by the absence of the diastema. In addition, the foramen magnum was positioned in such a way as to allow an upright position.
Dart was convinced that he was facing a skull which, even if it still had some simian-like characteristics, must have belonged to a direct ancestor of man. However, he did not have the courage to call that individual "man" and, betraying his Australian origins, gave him the scientific name of "Australopithecus africanus" which means Southern monkey that comes from Africa. It was therefore Dart who first coined the name Australopithecus to designate this particular kind of quasi-men and, shortly after, the detailed description of the characteristics of the find appeared in a famous article published in the prestigious scientific journal Nature, in 1925.
Dart, however, because of that article was marginalized by the scientific community, because in it he had dared to affirm that man had African ancestors, but the reason for so much aversion towards the new discovery was also due to the fact that paleoanthropologists, especially those British, were conditioned by the discovery of a fossil skull some years earlier in England.
In 1912 a young amateur archaeologist announced that he had found in Piltdown, a place a few kilometers from London, in well-established and deep sediments (therefore not very recent), together with bones of extinct mammals, several fragments of a skull with human features and a jaw, broken into several parts, of a simian type. It seemed that it was precisely that "missing link" of the human species that some scientists had been looking for for some time and that had never come to light. In reality he was faced with a clever mystification.
Many well-known paleontologists let themselves be fooled by a well-organized joke, because they were presented with just what they expected to find. Other paleontologists, less obsessed with the "missing link" idea, proved skeptical, but failed to prove that there was a scam because Piltdown Manwas immediately placed under lock and key in the natural history museum in London, where it remained until 1953. Only on that date was it finally possible to subject the find to a thorough examination which proved, without a shadow of a doubt, that neither the jaw nor the skull were very old. The age of the find was checked with the fluorine dating method, which revealed that the skull and jaw were not contemporary. Later it was ascertained that in fact it was a jaw of a modern orangutan and a skull that had belonged to a human individual who lived between 1200 and 1300. Furthermore, under the microscope, it was also possible to observe the signs of the file that had reduced the teeth to mimic wear as well as the counterfeiting of the color that was used to make bones look like fossils that were not fossils.
Returning now to the South African discovery of the Child of Taung, Dart, who knew his business well, knew perfectly well that, as children, chimpanzees and humans are much more alike than adults. However, the dimensions of the fossil skull, even taking into account the young age, were such that they could not be considered those of a man, but on the other hand they could not even be those of an anthropomorphic ape, also because the anthropomorphic apes all live in the forest. tropical and this type of forest, for millions of years, was no longer present in South Africa.
When Dart took his find to London and realized that the scientific community of the place had received his discovery very coldly, disheartened, he thought of returning to teaching anatomy at the University. It was then that a certain Robert Broom, a doctor with a passion for anthropology, managed to convince him not to give up the fight and to continue with him the search for human fossils. The two collaborated for about twenty years and unearthed numerous fossil remains of the genus Australopithecus.
The South African places that provided sufficient material to definitively establish Australopithecus' hominid nature were Sterkfontein, Makapansgat, Swartkrans, and Krom-draai. From here came not only many fossils ascribable to the genus Australopithecus africanus, but also a somewhat different form of Australopithecus which was assigned the name of Australopithecus robustus.
In the years following the discoveries of Dart and Broom, remains of Australopithecus were also brought to light in East Africa where the Leakeys worked. The first such finding was identified in a place in Tanzania called "Olduvai gorge", in 1959, by Mary, Louis Leakey's wife, on a day when her husband was unable to go out because he was bedridden by malaria. When Louis saw the find he immediately understood that it was an Australopithecus, but he still wanted to give it a proper and exclusive name and called it Zinjanthropus boisei, that is "man from Zinj", from an Arabic word with which East Africa was indicated, while the specific name referred to Charles Boise, the London-based financier of American origin who subsidized his research. The age of the fossil was estimated with the potassium-argon method and fixed at around one million eight hundred thousand years.
The name of Zinyantropo, assigned by Leakey to the find, did not last long because anthropologists, noting a strong resemblance to the robust Australopithecus of South Africa, renamed it Australopithecus boisei . Subsequently, other jaws and skulls of the same type were found near Lake Natron in Tanzania, and even a little further north in the Omo Valley, at the northern limit of Lake Turkana (formerly Lake Rudolph).
The Australopithecus were therefore present both in southern Africa and in eastern Africa, but only with the robust type, while fossils of Australopithecus africanus have never been found outside the southern African area.
Today Dart is considered the initiator of modern paleoanthropology as with him this discipline was addressed on a rigorous scientific basis. After the findings of South Africa and East Africa, the studies focused mainly on the deepening of the knowledge of the Australopithecus, and Dart was lucky enough to experience this fascinating period of paleoanthropological research in its entirety: he died, in fact, in 1988 at the age of ninety-five.
11. THE BEHAVIOR OF AUSTRALOPITHECIANS
The strange thing is that the South African sites where the remains of Australopithecuses were found were always also full of bones of various other animals including antelope, vervet, leopard, hyenas, turtles, crocodiles, etc. How can this concentration of bones be explained? Were Australopithecines predators of other animals or were they themselves the prey of ferocious animals? A certain answer has not yet been given, but the second hypothesis is favored.
Two small and round holes had been observed on an australopithecus skull, about two and a half centimeters apart, which seemed to have been left by the teeth of predatory animals: instead of making hypotheses, an expert local geologist began to measure the distance between the canines of a number of predators present in South Africa at that time. He was thus able to ascertain that the holes left on the Australopithecus skull fit exactly to the distance between the canines of the fossil leopard.
It is known that leopards have the habit of dragging their prey up trees to be able to devour them, with tranquility, out of the reach of carrion eaters. From here, while the animal is being torn to pieces, the bones fall to the ground. Now, since the South African lands in which the Australopithecus fossils were found are all karst soils, i.e. lands in which large trees grow right in correspondence with cracks in the soil that lead to deep caves where water stagnates, it is not to be excluded. that the bones of the prey, fallen from the tree, may have slipped into the cracks in the ground to accumulate in the caves below, just where today it is possible to find fossils in abundance.
Australopithecus africanus appeared about 3 million years ago and became extinct about 2 million years ago. The one million-year valuation that Dart gave to his find today is considered a dating by default, while at that time it was hard to believe that an individual with human characteristics could already be present a million years ago.
Australopithecus africanus was similar to its predecessor, Australopithecus afarensis: he was one meter and twenty tall, and weighed about thirty kilograms but males and females, although still having different sizes, no longer showed such a marked sexual dimorphism as that which had been found in afarensis. The head also showed more human than ape-like characters and therefore it must have been a hominid more evolved towards mankind than towards apes. It had also been observed that the arrangement of the set of teeth was parabolic, as in man, and not U-shaped as in anthropomorphic apes, and the size of the molars was such as to suggest that this individual had lived in the savannah. where the nourishment consists mainly of nuts and hard grains. Finally, the volume of the skull was about 450 cc.
The African Australopithecus became extinct, as we have said, two million years ago, perhaps because it was beaten by competition with the baboons who lived with it in the savannah and exploited its own food resources, or perhaps as a result of a profound modification of the climate. which made those places drier and consequently poorer in food.
We have evidence that a little more than two million years ago the climate in Africa generally became drier and this new habitat had to favor the development of larger forms of Australopithecus suitable for a coarser diet. And indeed, as we have seen, more robust and larger Australopithecus fossils than Australopithecus africanus were found in various locations in southern and eastern Africa. As will be remembered, they were given the names of Australopithecus robustus and Australopithecus boisei respectively.
These were two species of Australopithecus very suitable for the living conditions of the arid savannah and poor in food resources as, in addition to being more massive than their predecessors, they also had very powerful chewing muscles so as to require additional support to attach to the skull. The cranial vault of the Australopithecus of Boise has in fact, on the top, a strange crest which is interpreted as a support for the attachment of the masticatory muscles. This characteristic led the Leakeys to think that Australopithecus boisei was able to grind and crush very hard food with force, and for this reason he was given the nickname of "Nutcracker". These hominids in reality had adapted to a hypervegetarian regime that forced them to a prolonged chewing of large quantities of poorly nutritious foods; in other words, they were forced to make up for the lack of energy with a very abundant diet that required a highly developed masticatory system.
In summary, we have seen that Australopithecus robustus inhabited Southern Africa, while the boisei lived in East Africa: both became extinct about a million years ago, but lived, since their appearance, together with another hominid, and precisely to what is considered our true direct ancestor: Homo habilis.
12. THE EVOLUTIONARY LINES OF THE PRIMATES
At this point, before talking about the genus Homo, we must briefly analyze the evolution of what were the ancestral species of the hominids, that is the animal species that preceded the Australopithecines.
Man, as we know, belongs to the order of Primates, that is, to that group of animals to which monkeys also belong. The origin of these animals can be traced back to the end of the Mesozoic, about 70 million years ago.
At that time Europe and North America were still united in the supercontinent of Laurasia and along the equatorial belt that crossed it, extensive forests of Angiosperms, plants with flowers, were forming. These were invaded, unsurprisingly, by a large number of insects who discovered in the tree with flowers a very favorable ecological niche due to the abundance of food available. The insectivores that previously lived on the ground later found their natural habitat on those same trees. These, in turn, gradually adapted to the new environment, developing prehensile legs and considerable agility, transforming themselves into Pro-Monkeys which therefore originated in the northern continents and not in the south, where they moved only later, that is, when the geographical aspect of the lands emerged changed attitude.
In Montana, on a hill called Purgatory Hill by paleontologists, due to the difficulties encountered in the research and extraction of fossils, some teeth and fragments of small jaws were found referable to an animal slightly larger than a squirrel, which it could represent the progenitor of all living primates. To extract those few fossil fragments it was necessary to sift tens of cubic meters of land: hence the name of Collina Purgatorio assigned to that place.
This ancient Primate, who was given the by no means original name of Purgatorius , lived at the end of the Cretaceous period, when the dinosaurs had not yet completely died out. It would resemble an arboreal species still living in South Asia: the Tupaia, or an animal that was once classified among the Insectivores (together with the hedgehog and the mole), but which today is considered more similar to the Prosimians.
During the next geological era, the Cenozoic, the Primates rapidly diversified, but their evolutionary history was hardly reconstructed as the fossil remains of these animals are very scarce. The shortage of primate fossils depends on the fact that they are arboreal animals that lived in the forest, that is, in a place that does not lend itself to fossilization at all as the corpses are quickly destroyed both physically because eaten by other animals, and later to chemical transformations that dissolve bones before they can turn into fossils.
Fossilization is a phenomenon that requires particular environmental conditions to be able to take place. The ideal conditions are represented by the death of the animal near a volcano that provides its cover under a rain of dust and ashes, or on the shore of a lake where the still fresh corpse can be covered with mud or finally inside a damp cavern that a sudden collapse will permanently seal.
The flesh of the animal, which has just died, is soon devoured by small animals that live in the damp soil without, however, the bones undergo alterations; at this point, the non-mineral part of the bone, ie the protein collagen, undergoes a process of chemical transformation and is washed away by the circulating water. The bone then becomes porous and brittle and can be destroyed easily, which in fact happens in most cases.
If the bone exceeds this critical moment and if the circulating waters are rich in salts and their pH is neither too acidic nor too basic, the salts precipitate in the interstices of the bone and when all the pores have been filled it is petrified and has become a fossil. Fossil bones are therefore not bones, but stones.
Despite the few findings available, paleontologists have still managed to reconstruct the evolution of the prosimians through some fossils, attributable to animals no larger than a cat, found both in America and in Europe. In particular, some of these animals, classified as belonging to the genus Adapis , lived in central Europe, about fifty million years ago. These are small arboreal primates that are presumed to have been the progenitors of the Lemurids, a family of Pro-monkeys currently living in Madagascar.
About 40 million years ago the Pro-Monkeys experienced a sudden decline produced, presumably, by a gradual reduction of the forest environment, but perhaps also by competition from other Primates characterized by greater brain development and structural modifications of the extremities of the limbs.
These new animals were the progenitors of the Platirrine monkeys, also called New World monkeys, whose evolutionary history is practically stuck in the Miocene, that is, at the time when finds quite similar to living species were found. These are monkeys with a long prehensile tail and wide nostrils (hence the name of Platirrine).
The Catarrine monkeys (that is, with the narrow nasal septum), also called Old World monkeys, originated in Asia (if we want to give credit to some fossils collected in Burma), about forty million years ago, but soon moved to Africa where they still live. During the Oligocene, that is, approximately 30-35 million years ago, this genus of monkeys certainly already inhabited northern Africa because there is the location that has provided the highest number of fossils of Catarrine monkeys: it is the El Fayum region, Egypt.
The most important finding from the evolutionary point of view, carried out in that region, refers to a fossil which has been given the name of Aegyptopithecus : it is an almost complete skull of an archaic monkey that lived thirty million years ago which, according to some paleontologists, it would represent the progenitor of both modern anthropomorphic apes and man.
From this ancient ancestor a rather wide and varied range of primitive monkeys would have descended which today are all classified with the generic name of Driopithecine ("oak monkeys") and whose first specimen was found by Louis and Mary Leakey in 1948 on an islet of Lake Victoria in Kenya. The very famous Proconsul would also be part of the Driopithecine group.
Proconsul, whose name means "before Consul", referring to a chimpanzee named Consul who lived in the London Zoo, is the oldest fossil record of a primate without a tail and is believed to be the direct ancestor of the current monkeys. anthropomorphic African (chimpanzee and gorilla) and man. It was assigned an age between 22 and 12 million years.
Instead, the much discussed Ramapiteci would be found on another evolutionary line. In this case, it would be a question of several species of archaic monkeys, of small dimensions, which most likely had already reached the erect position, or almost, and whose first fossil representative was found in 1934 on the Siwalik mountains in Asia (at the foot of the Himalayas ), by an Indian geologist named Vinajak Rao. The name Ramapithecus, which derives from the Indian deity Rama and the Greek word "pithecos" which means monkey, was however assigned to him by a student of Yale University, this GE Lewis. Other specimens similar to Ramapithecus, which was given the name of Sivapithecus(but perhaps they are female Ramapitecine), were later found in Europe and Africa.
The Ramapiteco, more than any other, has fueled the controversy on the origin of hominids. At the beginning only fossils of the teeth and some fragments of the skull and jaw were found and on the basis of these scanty finds the approximate dimensions of the body were calculated. It was therefore concluded that it must be an animal no taller than a meter that lived in trees, but that perhaps it was also at ease on the ground because the teeth revealed the presence of a diet also made of hard foods as they could be. the grains, which, in fact, are collected on the ground. Based on the rounded shape of the "human" type dental arch, at first it was considered the true ancestor of man, but today it leans towards another thesis.
13. ONE PER CENT HUMANS
Recent studies, conducted on proteins and nucleic acids, have shown that the chimpanzee and the gorilla look much more like humans than the orangutan or gibbon. This discovery has upset what was the traditional subdivision of today's hominids into two families: on the one hand man (the only species of the genus Homo that survived natural selection) and on the other the anthropomorphic apes (chimpanzee, gorilla, orangutan and gibbon). This scheme actually stopped at the simple morphological analogy of the whole, that is to the external appearance, while today it is possible to carry out very in-depth studies on the organic molecules that are the basis of the anatomical differences of living organisms and then proceed to a classification of these more rigorous and detailed.
Molecular biology work began as early as 1967, when two young biochemists named Vincent Sarich and Allan Wilson of the University of California at Berkeley, having compared the proteins present in the blood of apes with those of man, concluded that gorilla, chimpanzee and man were very similar to each other, while there were more marked differences with orangutan and gibbon. Furthermore, on the basis of their measurements, they also managed to establish that man would have separated from other primates only five million years ago. Therefore, according to the studies of the two American scientists, man and the two African anthropomorphic apes should have still had a common ancestor in very recent times. For paleontologists, this claim was absurd because all the fossil and geological evidence indicated that the separation between the two evolutionary lines had occurred about twenty million years ago, and not just five as Sarich and Wilson asserted.
The work of the two American researchers was based on a very simple premise, namely the fact that the differences found within a given protein molecule, present in organisms of different species, should have been greater the further away the time had been. of the detachment of one species from another. And this is because the changes in proteins, due to the mutations of the genetic patrimony, should accumulate over time at a constant rate.
But how could the moment of separation between two different species be precisely determined? More precisely, how did Sarich and Wilson establish that African apes separated from humans only 5 million years ago?
The suggestion on how to proceed came from Linus Pauling, one of the greatest scientists of our century, winner of two Nobel Prizes (the first in 1954 for chemistry and the second in 1962 for peace) and recently died at the age of ninety-three. He began his long scientific career as an atomic physicist but then he dealt with various subjects and eventually also with biochemistry, focusing in particular on hemoglobin and blood proteins. Together with the biochemist Emile Zuckerkandl he studied the correlations existing between DNA and protein structures and intuited that DNA could have constituted a kind of molecular clock since the mutations that occur on it, being random events (such as those that occur in radioactive substances), should have accumulated regularly.
In radioactive substances, atoms are transformed at a constant rate into non-radioactive atoms, and once the decay rate is known, which is normally expressed through the so-called "half-life" (or semi-transformation) period, it is possible to estimate the passage of time. by measuring the amount of radioactive substance remaining in a given sample.
Potassium-40, for example, has a semi-transformation period of 1.3 billion years and this means that a certain amount of this particular isotope of potassium, present in a rock, remains after one billion and three hundred million years only half, while the rest turned into argon which is a non-radioactive element. Argon is actually a gas that is normally released into the air, but when it forms in volcanic rocks it gets trapped there. Therefore, by accurately measuring, in a volcanic rock, the amount of residual potassium-40 and that of argon-40 (which, to be precise, is the isotope of argon that derives from the decay of radioactive potassium), it is possible to trace the age of the rock, the period of half-transformation of potassium-40 being known.
The molecular clock does not measure a decrease, as occurs in radioactive substances, but an accumulation. The difficulty, in this case, was to calibrate the clock itself, that is, to establish the rhythm at which the time was beating. Sarich and Wilson after extensive research were able to determine the speed with which the differences on the different proteins accumulated. For example, they were able to establish that cytochrome c (a particular protein that plays an essential role in the cellular respiration process) changes one percent of its molecule every twenty million years, while hemoglobin does the same in just six million years. years. At this point all that remained was to set the clock in motion, that is, to choose the moment from which to start it. This had to correspond to the date of a fork in the family tree known with good certainty on the basis of conventional techniques. It was therefore decided to start counting time from thirty million years ago, that is, from the time when, according to paleontologists, the anthropomorphic apes separated from the other apes.
Now let's admit, to simplify the reasoning, that in these thirty million years which, as we said above, separate us from the time when apes and common apes still had a common ancestor, thirty amino acids along a given protein have changed. If this were the case, since the time span was constant, the changes would have followed one another at the rate of one every million years. Having established this, if it were found that on that same protein, present in African apes and man, there were only five different amino acids it would be clear that five million years should separate man and African anthropomorphic apes from the common ancestor.
Molecular anthropology studies have recently focused on DNA structures. Now, as everyone knows, each living species has its own DNA that characterizes it and two different species have their respective DNA the more dissimilar the more these species are on the evolutionary scale. For example, between horse and donkey, which are two very similar animals, even in outward appearance, and which therefore should have differentiated very recently from a common ancestor, the respective DNA molecules actually differ very little. On the other hand, those animals that presented a very different genetic code should have differentiated themselves from the common ancestor in very distant times.
Today the technique used to compare the DNA of two different species is called "hybridization" and, for example, in the case of man and gorilla, it consists in heating the double helix of the DNA of these two organisms until the separation of the strands that form. A single strand of the human DNA is then linked with a single strand of the gorilla's DNA and from this operation a hybrid double helix is obtained, that is, half human and half ape. The two filaments, when cold, rewind quite well but not perfectly, because there are some nucleotides that do not match and therefore do not bind. Heating this hybrid DNA shows that the temperature necessary for the separation of the two strands is a little lower than that which was used to separate the strands of a pure helix, as the number of bonds that hold the two nucleotide chains together is now less. In this way, a series of breaking temperatures of the hybrid DNA bonds are obtained which inform us of how closely the two species on which we are experimenting are closely related.
Also from these researches it is evident that chimpanzee man and gorilla are different only in appearance, while the difference is minimal in the DNA. Now one wonders how there can be such a small difference in the DNA and such a conspicuous one in the external appearance of these organisms.
Molecular anthropologists have their own theory on the evolutionary history of man and anthropomorphic apes which stems from an observation that had not been given too much importance in the past. The observation is the following: only the apes and humans are capable of being suspended from a branch with their arms and swinging. This movement is called "brachiation" and the non-anthropomorphic monkeys are not capable of it and move, in fact, on the trees, walking on the branches. Man, on the other hand, while not practicing this type of locomotion very frequently, knows how to do it and also in a casual way (just observe the children climbing in a playground or the athletes circling the rings and the bar). D ' on the other hand, not even apes spend much of their time hanging from tree branches. The important thing, however, is not the time these primates devote to brachiation, but the fact that they are able to adopt it whenever the opportunity arises.
Brachiation involves anatomical solutions of considerable complexity that only humans and apes possess. They have a very long collarbone, which makes the shoulder free to make all sorts of movements. This particular anatomy of the upper body not only allows brachiation but also the possibility of walking on the ground leaning on the knuckles of the upper limbs, something that the current apes do and that the distant ancestors of man probably did.
According to molecular anthropologists, man and anthropomorphic apes would descend from a brachiator who lived about twenty million years ago, that is, in the Miocene. The gibbon would have derived from it ten million years ago. Subsequently the orangutan would have differentiated and finally, about four and a half million years ago, man, chimpanzee and gorilla.
Unfortunately we do not have fossils that can be considered the direct relatives of modern anthropomorphic apes and that are also ancestors of man and furthermore we are unable to say whether they were brachiators or not of the few fossils of our most ancient ancestors.
It is certain, on the other hand, that Ramapithecus cannot be considered our direct ancestor first of all because, as molecular anthropology has also shown, it is too ancient to be and secondly because it would be on the evolutionary line that led to the orangutan which had now definitively separated from the one that the African anthropomorphic apes and man were by now about to traverse.
As mentioned above, the biochemical analysis was not limited to living tissue samples but could also be extended to a bone sample of Ramapithecus not yet completely petrified, revealing that this ancestral animal has more evident biochemical affinities with the orangutan than with the other apes. For this reason the Ramapithecus is currently considered the ancestor of the orangutan.
Today the most credited candidate for the role of common ancestor of chimpanzees, gorillas and Australopithecus is the Kenyapithecus, a hominoid who lived in Africa about six or seven million years ago (this is the time value on which even molecular paleoanthropologists today agree as a date separation between African apes and man) and who, as we have already mentioned, suddenly found himself separated into two groups by the sinking of the Rift Valley.
14. THE EVOLUTION OF THE HOMO GENRE
In 1961, in the Olduvai gorge, within the same site where the Zinjanthrope had been found a couple of years earlier, one of Louis Leakey's sons, Jonathan, found two fragments of the skull and an incomplete jaw of a hominid apparently more advanced than Australopithecus. The thinness of the bones, the small molars and the volume of the skull much higher than that of similar finds previously found, suggested that it must have been an individual of a slightly less robust constitution than any known australopithecus.
Judging from the place of the discovery (a level of the ground slightly lower than that where the Zinjanthrope was found), the fragment of the skullcap and the jaw of what will be called, in honor of its discoverer, the "child of Johnny", it must have belonged to an individual a little older than the Zinjanthrope, but at the same time more evolved than this.
A beautiful dilemma which, however, was solved two years later when, in an upper layer of the same deposit (dated about one and a half million years), a skull with a volume of 660 cm³ was extracted, alongside some worked pebbles. The processing of the lithic material was attributed to the hominid whose skull was brought to light, which was therefore called Homo habilis, that is "skilled man" and therefore able to use his hands with dexterity. The name was suggested by Raymond Dart who believed that the direct ancestor of modern man must be a hominid able to make tools and therefore to use the brain in an original way. Since the remains of the underlying layer previously found looked very similar to those just discovered, these last ones were also attributed to Homo habilis.
Other remains of Homo habilis were found in subsequent years both in East Africa and in South Africa: among these a skull, very well preserved, discovered in Kenya in 1972 by the other of the Leakeys' sons, Richard. The fossil was attributed an age of nearly two million years.
As we have already mentioned above, the discovery of the most advanced hominid bones of the Australopithecuses suggested that around two million years ago two types of individuals lived on the same territory, both with human characteristics, but somewhat different in details: some had a small brain and large molars, and they were the Australopithecus, the others had a large brain and small molars, and they were the hominids of the genus Homo. The former would have become extinct within a million years, the latter would have evolved to become today's humans.
About two and a half million years ago in Africa the climate changed for the umpteenth time and the savannah became more arid and consequently poorer in tender foods that were the favorite food of the African-type Australopithecines. In the new environmental conditions, while Australopithecus boisei (i.e. the robust form of Australopithecus) which fed on a diet made up preferably of vegetables and hard seeds, was equipped to cope with the difficulties that arose, Australopithecus africanus instead found itself in full crisis. How to survive?
The answer is always the same: changing. Mutations, as will be remembered, are those sudden and unpredictable changes in the genetic heritage that occur continuously in the DNA and which are then reflected on the physical structures of individuals. Normally these changes produce subjects less suited to the environment, but if this is in the process of transformation, the new forms may be particularly at ease thanks to the new physical requirements provided to them by the mutations. This could have happened in the case of Australopithecus africanus which unexpectedly found itself in difficulty in an arid environment poor in tender food. Therefore, according to the opinion of some illustrious paleoanthropologists, through some mutations, he would have become Homo habilis.
The mutations that followed on Australopithecus africanus were undoubtedly varied but one was decisive over all the others: the enlargement of the brain. This increased, in Homo habilis, by 50% compared to that of its predecessor. Such a disproportionate development of the brain, which had never occurred in any other animal and which will never occur later, will allow to effectively solve the problems that the new environmental situation was producing. These were basically problems related to the search for food.
Tender foods of vegetable origin were no longer there; there was, however, an abundance of meat. In fact, the savannah suddenly found itself inhabited by endless herds of herbivores who took advantage of an environment favorable to them to multiply. Most probably it was not necessary for Homo habilis to hunt animals to get food, as was originally thought: the ground must already be full of the carcasses of those that died of natural causes or killed by carnivores and then abandoned before come completely stripped. The Homo habilis to obtain the meat perhaps had to simply compete for it with hyenas and vultures which, as is well known, feed on carrion.
There was, however, a problem to be solved and not a trivial one. How to access the meat of large mammals covered by a thick and resistant skin that was almost impossible to cut with your teeth or nails? The African Australopithecus was certainly not equipped with claws suitable for penetrating into tissues and the canines, small and weak, were unable to tear the skin and tear the flesh from the bones of animals. All that remained was to use the brain which in the meantime had grown very large. Thus it was that the African Australopithecus, who had now become a "skilled man", began to manufacture stone tools, which facilitated access to the meat of dead animals. And while the African Australopithecus was transformed into Homo habilis, the boisei continued to chew nuts and hard grains, meanwhile becoming prey to the leopard and the other carnivores of the savannah. In this way it will eventually become extinct completely.
Today paleoanthropologists have sufficient fossil records available to reconstruct the physical structure of Homo habilis. It must have been an individual five feet tall and weighed about fifty kilograms. It was therefore about the size of Australopithecus robustus, but its bones were much lighter. He had a perfectly erect gait, the cranial capacity was around 700 cm³ and the face appeared much less prominent than that of the Australopithecus.
Above all, a very broad forehead gave the sensation of being in the presence of a human being, a sensation which, in the case of Australopithecus, had never been experienced before. Even the set of teeth was very similar to that of modern man and this is precisely what leads us to believe that the diet of Homo habilis was a little less vegetarian than that of Australopithecus and that for this reason it should also feed on meat.
With Homo habilis appears for the first time that characteristic which is considered a fundamental prerogative of the human race, namely the production of tools. To date, no evidence has been gathered that Australopithecus was able to make tools out of chipped stone, nor any living animal, not even the chimpanzee, which is also capable of tearing branches from plants to insert them into termite mounds and capture the ants that it then eats, is able to voluntarily manufacture tools of any kind, nor to keep those that have proved effective in certain circumstances. In other words, no animal is able to predict the future as man does.
But from which ancestral species does Homo habilis derive ? As we have seen, according to some scholars, Homo habilis derives from Australopithecus africanus. According to others, the Australopithecus afarensis would have given rise to two evolutionary lines: on the one hand the Australopithecus with the Africanus first, and the robustus and the boisei then, and on the other hand the Homo habilis, which would subsequently have differentiated first into Homo erectus and then in the current species of Homo sapiens. Finally, according to a third group of paleoanthropologists, the Australopithecines and the Hominids of the genus Homo have had an independent evolution without any direct relationship. Instead, they would have had a distant common ancestor, not yet identified.
Recent discoveries have shown that Homo habilis not only made stone artifacts but, most likely, that he was also capable of building camps. This was deduced from the discovery in Olduvai of a stone circle that would represent the remains of one of the first houses built by man.
15. THE LANGUAGE
"The words - as Richard Leakey also says - unfortunately do not fossilize". Therefore, we will never be able to know for sure when verbal language originated. However, we have some indirect evidence, represented by the artifacts made by our ancestors and by the changes in their anatomical structure, which allow us to formulate some hypotheses on how articulated language could have been born and developed.
The first man-made stone tools were found, along with his fossil bones, at Olduvai, and are two million years old, but even older ones were later found. These are the very famous "chopper" (English word that means accept, butcher's cleaver), pebbles of lava intentionally chipped to obtain a sharp edge. These worked stones were most likely used by Homo habilis to cut the skin of animals and to remove the flesh from their bones, but perhaps also to cut and sharpen the branches of trees.
The tool, unlike the simple tool, implies the presence of a conceptual thought, that is, the need for an idea of what you want to achieve in the mind of the operator. This idea will then become an object worked through an ordered series of successive actions. Is it necessary to know how to speak to perform these actions? Maybe yes.
To make a stone object, for example, you must first identify a pebble of the appropriate size and shape and then look for a suitable striker to hit the pebble. Furthermore, it is necessary to operate in such a way that the blows are inflicted under various angles and with adequately calibrated energy. Finally, it is necessary to control the shape that the object is assuming as a result of the chipping. All this requires an intellectual activity that is anything but simple.
Now, it is evident that the availability of a worked object gives the owner the advantage of having easier access to the finest food resources and this obviously facilitates the struggle for existence. But the machined object is not something that is genetically transmitted, as could be the largest and most robust teeth or the erect position: its realization therefore must be learned from previous generations who in turn must have an effective means to teach it. . And what better way to transmit information than that represented by verbal language?
The manual activity of Homo habilis does not end, however, with the construction of choppers. In more recent sites, in fact, better finished stone objects came to light, such as "chopping-tools", obtained by hitting the pebbles on both faces instead of just one. Subsequently, with the Homo erectus, the refined "amygdale" stone objects expertly finished on the whole core of the pebble appeared: for this reason the amygdale is also called "double-sided". It has never been possible to understand well what this strange stone object could be used for with the cutting edge that runs all around it making it difficult to hold in your hand without getting hurt. According to some, the amygdale, tied to a stick, could have been used as an ax, but careful observation under the microscope, at the point where the wood should have been grafted, showed no signs of wear. Most likely it was used as a throwing tool, but it may also be of no use: perhaps it was just a beautiful tool to be proud of for being able to build it.
But primitive man, as we have said, was also capable of building more complex artifacts than chipped stones. The so-called "camps", that is, the rough stone walls that surround limited areas of circular land, were perhaps rudimentary dwellings in which Homo habilis could have stopped to make tools, or to take shelter from wild beasts.
Technology may also have had its importance in the origin of verbal language, but without a particular conformation of the larynx, man could never have spoken. Chimpanzees and gorillas, for example, are also capable of expressing simple concepts and manifesting emotions, however they are unable to speak because their larynx is arranged in such a way as not to allow perfect modulation of sounds. The same thing happens in newborns, who would not be able to speak even if the psychic faculties allowed them.
In fact, phonation is only possible following the lowering of the larynx which produces an enlargement of the overlying pharyngeal cavity with consequent emission of sounds. In monkeys the organ of phonation is placed in an elevated position and precisely by virtue of this particular location of the larynx they are able to drink and breathe at the same time. The same happens in newborn babies who, as everyone knows, are able to breastfeed and breathe at the same time. Children can begin to speak, or rather, to correctly articulate words no earlier than the age of two, that is, from the age when the larynx tends to descend.
Recent studies have shown that the lowering of the larynx produces a flexion of the base of the skull that from flattened becomes curved. This phenomenon has been observed in children, who are born with a flat base of the skull, but then, with development, this begins to decline until it is finally settled at the age of ten. Now, in the skulls of the Australopithecus the downward curvature of the base of the skull has never been noticed, while in Homo erectus this flexion seems to be present even if in a not very evident way: therefore, most likely, he possessed the anatomical structures of basis for phonation. As for Homo habilis instead, it was not possible to carry out a similar examination due to the lack, among the fossil finds, of complete skulls of the base.
If nothing can be said about the position of the larynx of Homo habilis , on the other hand, the two areas of the cerebral cortex responsible for the control of articulated language seem to be present in this hominid. These are the "Broca Center" and the "Wernicke Center", named after the two researchers who discovered them in the last century. They are located on the left side of the brain which is also the most developed. In addition to the phonation centers, the fact that the majority of the human population is right-handed and the use of the right hand is controlled by that cerebral hemisphere also contributes to the greater development of the left side of the brain.
Unfortunately, the brain, like the word, does not fossilize. So no one has ever been able to directly examine the brain of an extinct animal. However, sometimes we can observe the external configuration of it in what are called the "intracranial casts". The brain during growth shapes the skull within which it is placed, leaving the mold of its structure on it. Now it can happen, during the fossilization, that the skull is filled with sand which subsequently consolidates forming the internal cast of the skull. This represents the exact duplicate of the size and shape of the inside of the skull, which can also be considered a kind of stone brain of which only the outside can be observed. Some scholars,Homo habilis , they can see traces of the lobes and convolutions of the brain.
Many scientists actually call for caution as the meninges that surround the brain are very thick membranes and therefore it is very unlikely that the imprints of the convolutions and blood vessels of the brain can form on the skull. What is printed on the inside of the skull - they say - most likely are the vessels of the walls of the skull itself and not those of the brain.
Some paleoanthropologists are of the opinion that verbal language did not develop through a slow and gradual evolution that began more than two million years ago, but suddenly and very recently. According to these scholars, language appeared only 35,000 years ago when man already possessed forms of culture similar to those we know today.
16. THE HOMO ERECTUS
As we have seen, Homo erectus succeeds Homo habilis. The denomination of "erectus", reserved for this hominid, dates back to the fifties, when it was believed that the Australopithecus were not yet perfect bipeds, but that they walked with the help of their upper limbs, as anthropomorphic apes currently do. Homo erectus had a brain with a volume greater than 1000 cm³, that is , slightly less than ours, and lived between one and a half million and 200,000 years ago, the latter age when Homo sapiens appeared on the scene.
The first fossil of Homo erectus was found in Java by a Dutch doctor who had been transferred to those lands because he was convinced that there should be the "missing link" between man and ape. Ernst Heinrich Haeckel had spoken of this missing link, one of Darwin's great supporters, who had hypothesized the existence of an ancestral creature, which he called Pythecanthropus, and which should have had, as the name also said, half characteristics of ape and half human characteristics.
The story of the Dutch doctor, named Eugene Dubois, deserves to be told in full because it is incredible. This strange character, since he was a boy, had been passionate about Darwin's evolutionary theory and was convinced that the Neanderthal fossil was actually a human ancestor, but that even more ancient forms must exist, that is, the type of what Haeckel called Pythecanthropes. At that time Indonesia was a Dutch colony and Dubois knew that there lived a kind of great ape similar to man, and whose name he also pointed in this sense. It is the orangutan (a word which in the local language means "man of the forest") and therefore, through a reasoning devoid of any logic, he thought that the ancestor of man should also have been in the same places.
The young Dubois initially tried to be sent by the government of his country to Java as director of a scientific expedition, then, having failed to obtain the post, he asked to be sent there as a military doctor. And he was satisfied.
By a truly incredible stroke of luck, he actually found in 1891, along the banks of a small stream, the river Solo, a human skull and some teeth. The following year he found a human femur in a nearby area and within the same rock formation. At that point, he believed he had identified the missing link and called the new hominid Pitecanthropus erectus, name that means "monkey-man who stands upright". The name Pitecanthropus seemed perfectly appropriate because the skull was too big to be that of an ape and too small to be that of a man. On the other hand, the femur, coming from the same formation, was essentially modern, which meant that its owner walked standing upright. Hence the specification of "erectus" given to the find.
Other fossil remains, similar to those of Dubois' Pythecanthropus, were later found in different parts of the world and each received its own name. The artifacts found in China, for example, were given the name of "Peking Man", or Sinanthropus; in Germany, Mauer's famous mandible was discovered in Heidelberg, and in Africa the oldest representatives were found: in the Koobi Fora deposit east of Lake Turkana a skull was found to which the age of 1,600,000 years has been attributed . All these hominids today are classified as Homo erectus and have nothing to do with apes.
Homo erectus was not only capable of chipping stone, which it did with greater skill than its predecessor habilis, but it also learned to systematically use fire. The use of fire greatly benefited this hominid, because it allowed him to push himself to conquer cold places and also because it allowed him to better exploit and preserve food.
About 200,000 years ago Homo erectus was definitively supplanted by Homo sapiens with which our story ends.
Between 400 and 300 thousand years ago, more modern-looking forms of Homo erectus appeared in various regions of the planet that paleoanthropologists do not yet know whether to consider Homo sapiens or simply more evolved forms of Homo erectus.
Homo sapiens subsequently differentiated into two subspecies: Homo sapiens neanderthalensis, whose fossil remains do not have an age prior to 100,000 years, and Homo sapiens sapiens appeared between 200 and 140,000 years ago in Africa.
Africa has therefore been the cradle of man twice: once with the Australopithecuses, when, especially in consideration of their upright position, these hominids were considered our closest ancestors and, subsequently, with Homo sapiens, our true direct ancestor.
Darwin's extraordinary intuition finally found its full confirmation. In 1871 he wrote:
In every great region of the world existing mammals are closely related to the extinct species of the same area. It is therefore probable that Africa was once inhabited by extinct apes, closely related to the gorilla and the chimpanzee. and, since these two species are currently man's closest relatives, it is likely that our ancient ancestors lived on the African continent rather than elsewhere.
