The story of the human journey - evolution is rewritten / Kate Wong

A flood of new insights is forcing scientists to redraw almost all the chapters in the story of human history

through the "mailbox" and up the "dragon's back", down the "slide" and on to the "riddle box". In the fall of 2013, the world followed, through tweets, blogs and videos, a team of scientists who navigated through these strangely named landmarks, located in the cave system called "Rising Star" on the outskirts of Johannesburg in South Africa. The narrow passages and steep shafts in the cave made the dangerous work difficult. And yet, the researchers set their sights on the big prize: the fossilized remains of an extinct member of the human family. Paleoanthropological fieldwork is usually done in secret. But this time the scientists published moving multimedia letters for all to see.

Cave explorers noticed the bones in September 2013 when they were surveying the lesser-known caves in this famous region of Israel, which has been named the "Cradle of the Human Race". The researchers were sure that the bones were important even before they knew their age and biological species (species), since most of the fossilized details of the human lineage contain skull fragments or bones from the neck down. This time bones of both types were discovered. The possibility of making a connection between a skull and the bones of a skeleton was enough to place this discovery in a prominent place in any textbook on the origin of man. But after the diggers began to uncover the bones, they realized that they had something even bigger in their hands. At the bottom of the cave were not the remains of a single individual, as they first thought, but the remains of many individuals - an entire population of ancient humans.

During two excavation expeditions, which lasted a total of four weeks, the team, led by paleoanthropologist Lee Berger of the University of the Witwatersrand in Johannesburg, removed more than 1,500 bones and bone fragments from their resting place, 30 meters below the surface, and brought them up to the expedition's laboratory tent. There the researchers cataloged the fossils and filled vault after vault with the remains of our ancestors. And yet, they have only scratched the surface. An unbelievable hoard of bones awaited them in the cave room. At this rate, the "Rising Star" cave system is emerging as one of the richest sites in human fossils ever discovered.

The exact significance of the findings is still unknown. Although the team involved the public in the disclosure efforts, it kept the scientific details behind the scenes. It is possible that the bones represent a biological species new to science, which, like the fossils uncovered by Berger and his colleagues at the nearby Malpa site a few years ago, sheds new light on the obscure origins of our biological type (genus), Gay. [See: "Our first” by Kate Wong, Scientific American Israel, August-September 2012.] And perhaps, due to the large number of individuals on the site, some pattern will be revealed that will reveal the structure of their social groups. It is likely that a comparison between the human remains and the animal remains at the site will clarify how they ended their lives in the cave. The answers are already on the horizon: the discovery team is now preparing for publication the official description of the excavations and the analysis of the bones.

We, the onlookers, still do not know how these fossils will rewrite the story of the origins of man, but history teaches us that they will indeed rewrite it. The discovery in the "Rising Star" is only the latest in a stream of findings that have been discovered since 2000, findings that undermine the pillars of the study of human evolution. New fossils add branches to our family tree. Climate data reveals the conditions under which evolution led to the development of the traits that characterize our ancestors. Research in primates is increasingly clarifying the exact cognitive differences between us and our closest family members: the great apes. Decoding DNA sequences illuminates the interrelationships that prevailed between ancient populations and hints at how evolution continues to change us. This flood of fresh insights forced the scientists involved in the field to practically rewrite all the chapters in the story of human plots, from the dawn of the human race to the victory of the intelligent man, theHomo sapiens, about the Neanderthals and other ancient species. Never has the science of human origins been so vigorous. Never has our story been so fascinating.

To appreciate how far paleoanthropology has progressed in recent years, let's go back for a moment to the late 90s of the 20th century. At the time, scientists thought they had a pretty good understanding of our evolutionary story. The human fossil record was quite rich (especially compared to the almost nil record of our closest living animals, the great apes), and the genetic evidence, which was workable, seemed consistent with the fossil story. The popular opinion at the time was that the first hominins (a group that includes modern man and his extinct relatives) appeared in East Africa about 4.4 million years ago, and in their wake our species evolved, Gay, a little over two million years ago. Hominins didn't leave Africa until just over a million years ago, after which they began to infiltrate other areas of the Old World. After settling in these new places, new species of Gay, including the Neanderthals of Eurasia. These species thrived for hundreds of thousands of years until a new species emerged from Africa and began to spread around the world. Much wiser, equipped with advanced technology and gifted with the gift of speech, the lambHomo sapiens the world by storm, when on his way to the top he lays a kidney on the Neanderthals and other ancient human species. There was no intermixing of the sexes, no children of mixed hybrids to carry Neanderthal genes to future generations. The new guard soldiers simply replaced the previous guard. On his way out of Africa, theHomo sapiens In competition with the hominins he met, at best, or killed them at worst. About 30,000 years ago, we were the only hominin standing on our feet. That's how the story goes, anyway.

However, the fossil evidence and the genetic evidence that has accumulated since then have undermined all the foundations of this summary, or even completely contradicted them. For example, seven-million-year-old fossils, found in the Jurab Desert in Chad, stretched the human fossil record by more than two million years and raised the possibility that hominins did not emerge in East Africa, but rather in the West. And the fossils from Malpa in South Africa, which are about two million years old, hint that the species Gay He himself began his journey in this part of the continent and not in the east.

Fossils from the Damanisi site in the Republic of Georgia (Georgia), dated as 1.78 million years old, prove that hominins began to leave Africa hundreds of thousands of years earlier than previously thought [see "A stranger in a foreign land", Kate Wong, Scientific American Israel, August-September 2004]. This therefore happened a long time before thatGay During its evolution it developed long legs, a large brain and a sophisticated "tool box", features that were previously believed to be the features that pushed its spread in the world. Another amazing discovery, of a species of tiny hominins that lived on the island of Flores in Indonesia until about 17,000 years ago, raised the possibility that our ancestors began to spread in the world outside of Africa even before the time that the fossils from Manisi teach [see “the smallest personKate Wong, Scientific American Israel, June-July 2005; "A new look at the hobbits of Indonesia", Kate Wong, Scientific American Israel, February-March 2010]. ToHomo fluoresiensis, as the remains from Indonesia are called, had an unusually small body and brain, traits it may have inherited from an Australopithecus-like ancestor that made its way out of Africa two million years or more ago.

But perhaps there is no chapter in the story of the past human journey that is written so dramatically as the plots of his rise to greatness Homo sapiens. The fossil evidence shows that our species was very far from being an evolutionary safe bet, a species destined to rule the world from the start. On the other hand, they paint a picture of a species that almost became extinct immediately after its formation due to climate change. Also the cognitive gap between Homo sapiens And among other ancient species was not as distinct as some researchers have imagined. Discoveries of sophisticated tools, such as leather polishing tools made from animal bones, reveal the fact that the Neanderthals were much more technologically advanced than we previously thought. And evidence that they decorated their bodies with paint, jewelry, and feathers confirms that Neanderthal societies were steeped in rich symbolic traditions that were once thought to be unique toHomo sapiens. The idea that the Neanderthals were dumb cavemen is therefore a myth.

And in keeping with the shared anatomy of the two species, genetic studies have shown that modern humans shared descendants with the Neanderthals. They did this frequently enough to result in the fact that today about 3% of the genome of non-African people is Neanderthal genome. Moreover, since different people carry different segments of Neanderthal DNA, the sum of all Neanderthal genetic material that has survived to this day reaches a much higher rate: at least 20%, according to recent calculations.

Neanderthals weren't the only ancient humans to squat Homo sapiens. The Denisovans, a group recently discovered after analyzing DNA extracted from a mysterious 40,000-year-old finger bone discovered in a cave in Siberia, also mated with our ancestors. Moreover, intercourse with early hominin species appears to have benefited theHomo sapiens, who in this way acquired genes that helped him survive: genes originating from Neanderthals, for example, improved the immune system. A certain genetic variant that came from the Denisovans helps Tibetans live at high altitudes.

But despite everything that links us to our evolutionary relatives, we have some features that set us apart. In this special issue of Scientific American Israel we explore the evolution of some of these characteristics that make us human: from our upright posture to our unique ability to cooperate. Our story has three chapters. The first examines our tangled genealogy and the factors that led to our branch surviving and in its way displacing all others. The second chapter reviews the differences between us and other primates and examines how these traits might have helped us thrive. And the third chapter looks into the future of human evolution in a world that offers plenty of repair options for almost everything, from loneliness to disease.

We hope you enjoy the story, produced over seven million years. This is not the last word, of course. Just as human evolution is accelerating, so too is the pace of paleoanthropological discoveries. But that's the only way to tell it.

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on the notebook

Kate Wong is a senior editor at Scientific American. She edited the special issue from which we bring you, in this Hebrew issue, the articles on human evolution.

The article was published with the permission of Scientific American Israel