Translation. Region: Russian Federation –
Source: Novosibirsk State University –
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Alexander Pilipenko, PhD, Head of the Inter-Institute Laboratory of Molecular Paleogenetics and Paleogenomics at the Siberian Branch of the Russian Academy of Sciences, explained how human evolution unfolded over millions of years and discussed the common ancestors of humans and apes. The audience learned about the divergence of their evolutionary paths and the changes Homo sapiens underwent over millions of years of development during his lecture, "Through the Pages of Human Evolutionary History," which took place as part of Darwin Week, a popular science marathon traditionally held at NSU in February. This year, the event was held for the first time on the new NSU campus. Pilipenko helped the audience understand the main stages of human evolution, from our primitive ancestors to modern humans.
Our distant relatives
Among the large groups of mammals, the largest order we are most closely related to are rodents and lagomorphs from the group Glira. Together with them, we, as primates, are grouped together in the group Euarchontoglira.
"It's a good relationship, because rodents are currently one of the most evolutionarily successful groups of mammals. They are true champions in terms of species count, total biomass, diversity, and reproducibility, and they have populated most of the planet. But we also have closer relatives—tree shrews and colugos. Unlike rodents, they can't boast of any particular achievements in territorial expansion or species diversity, but they have nonetheless survived to the present day, albeit with a very small number of species that have mastered a narrow ecological niche. The order of primates, to which we belong, comprises 380 species, which also inhabit a fairly narrow range. All, that is, with the exception of one—humans, who millions of years ago decided to stand out from the crowd and achieve every possible and impossible evolutionary success," explained Alexander Pilipenko.
Our most distant relatives are lemurs and lorises, which belong to the group of strepsirrhine monkeys. All others, including modern humans, belong to the group of swan-rhines. This is a fairly diverse group, and the first of the swan-rhines to branch off from our evolutionary path were the tarsiers, approximately 60 million years ago! From there, "nose-based evolution" continued. Forty million years ago, the common-rhynchus monkeys diverged from the monkeys of today's Old World. Another 15 million years later, our first distant ancestors diverged from this group. Gibbons emerged from this group 18 million years ago. Our common ancestor with the great apes existed on the planet 14 million years ago. The evolutionary paths of the ancestors of humans and gorillas diverged 8-10 million years ago, and those of humans and chimpanzees diverged 6-8 million years ago. They then evolved independently and in slightly different directions. Some evolved into modern chimpanzees and bonobos, while others evolved into hominids, including the genus Homo. Each group followed its own long evolutionary path. But while noses were the original ancestors, the tail has now fallen victim to progress.
Where did the tail go?
How is it that the most evolutionarily successful group of great apes, including us, can't boast a beautiful and functional tail? And at what point in our evolution did we lose it? As Alexander Pilipenko explained, approximately 20-25 million years ago, a single mutation occurred in one of our genes, causing the protein encoding the gene responsible for tail formation to suddenly begin to lose a small portion. This regulatory gene dramatically destabilizes the development of the part of the spine responsible for tail development. And as soon as a certain variant of this gene arises, tail development in apes and even other mammals studied is dramatically destabilized. In some individuals, for some reason, the tail continues to develop, in others it becomes underdeveloped, and in others it disappears altogether. In other words, this "broken" gene didn't immediately make our ancestors tailless. But eventually, subsequent mutations and evolutionary natural selection completed the process, and this trait became permanently fixed—we lost our tail, and none of our closest relatives regained it for 20 million years. Somehow, the absence of a tail proved so evolutionarily advantageous that it became permanently fixed at the genetic level.
"Missing link
Several million years passed between the time chimpanzees diverged from their common ancestor with ancient hominids and the emergence of modern humans. It was during this period that scientists of the past searched for the so-called "missing link" between humans and their ape-like ancestors. Modern researchers no longer seek proof of human evolution; they seek evidence that allows them to understand the evolutionary history of humans in greater detail. Alexander Pilipenko explained why.
— Previously, paleontologists, having found another creature that was somewhat similar to our ancestor, at first tried to integrate it into a direct line between some very primitive predecessor of man and modern people due to the presence of certain progressive traits. As such findings accumulated, it became even more clear that human evolution had indeed occurred. Currently, a large number of forms with intermediate meanings and with a mosaic combination of progressive and, on the contrary, primitive features among paleontological finds many times overlaps the necessary minimum that was necessary at the initial stage to prove this fact. Now scientists have to decide how to correctly group the discovered creatures and find a place for each of them on the evolutionary tree connecting primitive ancestors and modern people. Assessing their place in human evolution, scientists primarily pay attention to three classes of morphological features: changes in the body associated with possible adaptation to upright posture (spine, pelvic and femoral bones, structure of the foot), the skull and its brain part (structure, size, volume), as well as structural features of the hand, which should indicate that a person is becoming more and more capable of performing fine manipulations with his hands. It has been established that the ancestral home of humanity is Africa, and most of the creatures found that belong to this stage of evolution were found on this continent, the scientist said.
Our "pre-human" ancestors
Alexander Pilipenko listed some of the main ancient human ancestors whose remains were discovered by paleontologists.
Sahelanthropus is chronologically close to the last common ancestor of humans and apes. This hominid, who lived approximately 7 million years ago, possessed a number of advanced traits that were already associated with the beginnings of adaptation to an active upright posture during locomotion. This hominid was not yet fully bipedal. Nothing is known about the structure of its arm and hand. Despite this hominid having already begun to adapt to bipedalism, its brain size remained the same as that of chimpanzees and their close ancestors. No obvious differences were found in brain structure either. Alexander Pilipenko explained that this mosaic of advanced and archaic traits was characteristic of virtually all creatures that lived over the next 2-3 million years.
One of the earliest, relatively well-studied groups of our ancestors is the Ardipithecus. They existed over 4 million years ago. They remained as small as Sahelanthropus (approximately 120 cm tall). But they already showed clear signs of further adaptation to bipedalism, with changes affecting their hands, enabling them to perform more complex and subtle movements. This is evidenced by a unique find—skeletal fragments of a female, which paleontologists have named Ardi. It is considered one of the most complete skeletons of early hominids: most of the skull, teeth, pelvic bones, and limb bones are preserved. This allows scientists to conclude that the brain size of this human ancestor remains the same as it was 2 million years ago. Despite the changes toward bipedalism, the lower limbs still retain a completely ape-like structure, suitable only for tree climbing but not well suited for upright walking. However, a rigid arch is already beginning to develop in the foot, which, however, is still far from what formed in our closest ancestors.
A more advanced group of these early creatures are the australopithecines. Numerous species of australopithecines lived between 4 and 1 million years ago. It is believed that early humans evolved from them. Among them, there is also a "star"—a female named Lucy by scientists. Her skeleton is 40% preserved. Alexander Pilipenko noted that such finds are very rare and are of such high scientific value that scientists study them in great detail and comprehensively. Lucy was much better adapted to upright walking than Ardi. Her brain size, compared to Ardi, was significantly larger, primarily due to the parietal lobe. This is presumably related to upright walking and fine hand movements, for which Lucy was much better anatomically adapted. The hyoid bone, responsible for the development of the potentially complex vocal signaling system we call speech, was still in a state close to that of apes. In other words, australopithecines had not yet developed even primitive speech. However, they were already confidently walking on two legs—this was revealed by the astonishing discovery of the "Laetoli Tracks" in Tanzania, East Africa. This was a set of footprints of two individuals—an adult and a juvenile—left in volcanic ash 3.5 million years ago.
Another famous Australopithecus, nicknamed Harry, differs significantly from Lucy, who belonged to the early Australopithecus, while Harry belonged to the later Australopithecus, living contemporaneously with primitive representatives of the genus Homo. Surprisingly, primitive stone tools were discovered near Harry's remains, but it is still unknown whether they were related to him or were accidentally introduced. If this mystery is solved, it will become clear whether Harry was the first "non-human" capable of making stone tools. For now, most scientists are confident that this is not the case.
But Australopithecus weren't the only ones who shared the planet with early humans. The Paranthropus, apes of higher primates, also lived out their final days. For several hundred thousand years, they shared the same habitats with early Homo. They looked completely different from other "pre-human" human ancestors. Due to their specialization on coarse plant foods, their jaws and teeth underwent modifications.
Early humans
Alexander Pilipenko also spoke about early representatives of the genus Homo, who encountered their "pre-human" ancestors.
Homo habilis (2.4-1.4 million years ago) possessed an important skill unavailable to earlier hominids. They were capable of producing stone tools reliably using a specific technology. Importantly, they did this with the help of other tools. This is precisely what constitutes full reproduction. A chimpanzee can use a stick to knock down a fruit hanging high on a tree branch, but they would not be able to use a sharpened stone to shape the stick.
External changes were also significant. Compared to their pre-human ancestors, Homo habilis' brain volume increased from 350-400 to 600-700 cubic centimeters, and in some individuals, up to 800, yet their height remained the same—120 cm. The brain regions responsible for speech generation began to rapidly develop, but the structure of the larynx remained primitive. These creatures did not yet possess a fully developed, complex speech system.
The central creature in human evolution is Homo erectus (1.8 million to 143,000 years ago). This creature is characterized by a rapid increase in brain volume—from 850 to 1,200 cubic centimeters. This represents a completely different stage of development, as 1,200 cubic centimeters represents the lower limit of normal brain volume for living humans. Their height and body weight, however, remain the same as those of Homo habilis. Thus, a rapid increase in the ratio of brain volume and mass to body weight and size is noticeable. But the most significant achievement of Homo erectus is that they were the first members of the genus Homo to reliably expand beyond Africa and subsequently disperse across the planet.
Alexander Pilipenko spoke in detail about the development of Homo sapiens, who emerged approximately 300,000 years ago in Africa, evolving from Homo heidelbergensis. He then migrated out of Africa, gradually interbreeding with other human species, which, since the first and second waves of Homo erectus migration, have undergone their own evolutionary journeys. The scientist also explained how the populations of the continents, in all their diversity, formed. Particular attention was paid to the unique discoveries made in Denisova Cave (Altai Krai), which have changed our understanding of ancient human history. Here, in 1994, the remains of an extinct and previously unknown human species were discovered. This species not only coexisted with Neanderthals, but also had offspring, and the genes of these ancient creatures are still present in modern humans.
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