Modern Life, 50,000 B.C.

The Dawn of Us

Jean‑Marie chauvet had no reason to be surprised on the afternoon of December 18, 1994. He was walking along a limestone gorge in the Ardèche region of southeast France with two friends, looking for caves. The Ardèche region is shot through with caves, and Chauvet, who had grown up there, had been spelunking since he was 12. In 1988 he began a systematic survey of the region with Christian Hillaire and Eliette Brunei Deschamps, expert cavers themselves. In the six years that followed, they found a number of new caves, 12 of which were decorated with ancient wall paintings. December 18 was a cold day, so Chauvet’s team decided to explore a sunny area at the entrance to the gorge. It was not a particularly remote place; shepherds brought their flocks there, and presumably other spelunkers had been through many times. If anything spectacular was to be found, it should have been discovered long ago.

Chauvet’s team followed a mule path through the oaks and boxtrees until they reached a cliff, and there they found a hole. The hole was barely big enough for them to stoop their way inside, and they soon found themselves in a downward‑sloping passageway a few yards long. It might well have been a dead end, but among the rubble at the end of the passageway they felt a slight draft.

The three of them took turns pulling the rocks away from the passageway, lying on their stomachs, heads downward. Finally they cleared a way through, and Deschamps, the smallest of the three, wriggled her way forward 10 feet. She found that the passageway opened at its end. When she cast her flashlight ahead, the beam soared out into a giant gallery, its floor 30 feet below.

The cavers ran a ladder from the passageway down to the gallery floor and descended into the darkness. Stalactites and stalagmites glittered like fangs in their flashlights. Columns of calcite were coated with jellyfish‑like tendrils. They moved deeper into the cave. A mammoth suddenly lurched into the light. Then a rhinoceros, then a trio of lions. The animals were painted across the cave walls, some alone, some in giant stampedes–horses, owls, ibexes, bears, reindeer, bison–interspersed with the outlines of hands and mysterious rows of red dots. The spelunkers were familiar with cave paintings, but they had never seen anything on such a scale. They were confronted by a menagerie of at least 400 animal images.

The cave, which has since been named after Chauvet, is profoundly important, and not just for the paintings themselves. Archaeologists have measured the carbon 14 in the charcoal in the paintings and used it to estimate their age. People were painting animals on the walls of the Chauvet cave at least 32,000 years ago. That makes them the oldest paintings in the world.

The history of life is marked by dates like this one. They stand in a long row, like poles on a slalom course; any theory for the evolution of life must be agile enough to weave its way past them. The rocks of southwest Greenland show that life existed on Earth 3.85 billion years ago; those of the Karroo Desert in South Africa show that 250 million years ago almost all of life died out. The Chauvet paintings mark an event just as remarkable in the history of life: the moment our ancestors leapt into a world of art, symbols, complex tools, and culture–the things that make us most unique, most human.

The Chauvet cave and other archaeological sites that date from around the same time hint that this leap was sudden and long. The lineage that led to humans split from our closest living relatives, the chimpanzees, about 5 million years ago. It evolved in fits and starts, producing many branches that are long extinct and only one that has survived. Judging from the shapes of bones and sequences of genes, several teams of scientists have estimated that biologically modern humans evolved in Africa between 200,000 and 100,000 years ago. For tens of thousands of years, they left little mark on Earth except for the stone tools they used for butchering meat. Only around 50,000 years ago did they sweep out of Africa, and in a matter of a few thousand years they replaced all other species of humans across the Old World. These new Africans did not just look like us; now they acted like us. They invented tools far more sophisticated than those of their ancestors–hafted spears and spear‑throwers, needles for making clothes, awls and nets–which they made from new materials like ivory, shells, and bones. They built themselves houses and adorned themselves with jewelry and carved sculptures and painted caves and cliff walls.

Most of the great transformations in evolution, such as the origin of life or the Cambrian explosion, took place hundreds of millions, or even billions, of years ago. In comparison, this human transformation happened only yesterday. But it is just as significant. Modern humans have become the world’s dominant species, able to live just about anywhere on the planet. Our success is so staggering, in fact, that it threatens to destroy many other species. And while we may threaten the evolution of other species, we have also created a new form of evolution: the evolution of culture.

The First Moderns

Only in the last 20 years has the possibility of such a revolution become clear. Earlier generations of scientists had a very different idea of how modern humans arose. In the old view, modern human evolution began a million years ago. At that point, a single species of hominid, Homo erectus, lived in Africa, Asia, and Australia. Although H. erectus was spread out across thousands of miles, each population continued to keep at least some contact with its neighbors. As men and women from these scattered bands mated, the genes of H. erectus flowed across its entire range. No group became isolated enough to fragment into a new species of its own. Some populations may have taken on a distinctive look here and there as they adapted to local conditions. In Europe, for example, where humans had to cope with harsh ice ages, the people we now call Neanderthals had stocky bodies and thick, low‑browed skulls. In the tropics of Asia, on the other hand, populations of H. erectus became tall and slender. But together, the thinking went, all of these humans evolved into their modern form.

Neanderthal fossils can be found in Europe and the Near East from about 200,000 years ago to 30,000 years ago. Scientists initially believed that Neanderthals then evolved into modern Europeans, and along the way their tool kit evolved as well. Instead of the old stone tools and spears of the Neanderthals, the earliest Europeans (known as Cro‑Magnons) used exquisitely crafted tools made of many different materials, such as fishhooks made of antlers and bones or spear‑throwers with detachable foreshafts. Cro‑Magnons buried their dead in elaborate rituals and wore necklaces and other ornaments. The fossil record of human evolution was spottier in Asia and Africa, but researchers assumed that H. erectus also evolved into modern humans in those regions and developed the new technology at the same time.

But in the 1970s a few paleoanthropologists began to contemplate a radically different vision of human evolution. They proposed that Neanderthals and Homo erectus in Asia were actually two distinct species, and that neither was the ancestor of Homo sapiens.

At the Natural History Museum in London, for example, paleoanthropologist Christopher Stringer found that fossils of Cro‑Magnons looked less like Neanderthals than they looked like slightly older Africans. Instead of evolving from Neanderthals, Stringer proposed that modern Europeans descended from African immigrants. The Neanderthals who were alive 30,000 years ago did not evolve into modern Europeans, Stringer declared. They became extinct.

As Stringer stared at fossil skulls, a geneticist at the University of California at Berkeley named Allan Wilson was trying to reconstruct human history with biochemistry. He set out to analyze the DNA in human mitochondria–those energy‑generating factories of the cell that carry their own DNA. He chose mitochondrial DNA rather than any of the genes in the nucleus because it passes from one generation to the next relatively unchanged. Unlike most genes, which are shuffled between the chromosomes we inherit from both our parents, mitochondrial genes come only from our mother. (This is because sperm cannot inject their mitochondria into an egg.) Any differences between a mother’s mitochondrial DNA and her child’s can arise only when the genes spontaneously mutate. As different mutations build up through the generations, it becomes possible to use mitochondrial DNA to distinguish different lineages.

Wilson’s team analyzed samples of mitochondria from people throughout the world, sequencing the genes and grouping them together based on their similarity to one another. In the process they created an evolutionary tree of living humans. The branches of living Africans, Wilson discovered, all reached deepest into the tree of humanity. The tree suggested that Africa is the source of the common ancestor of living humans.

Most paleoanthropologists at the time might have gone along with this idea if Wilson had been talking about an early species of Homo that lived in Africa 2 million years ago, before any hominids had left the continent. But Wilson found that human genes were saying something very different. Once his team had constructed their evolutionary tree, they calculated how long ago the common ancestor of present‑day humans lived. They estimated the rate at which the mitochondrial DNA mutates, and then they compared the variations in the genes to judge how much mutation had occurred in the different lineages. Their molecular clock then gave them an estimate for the age of the first modern human: somewhere in the neighborhood of 200,000 years.

“Mitochondrial Eve”–as this common ancestor came to be known–was certainly ancient, but to scientists who championed a multiregional origin of Homo sapiens, she was far too young. None of the older Neanderthals in Europe or Homo erectus in Asia could have contributed their genes to living humans. But for Stringer, Wilson’s tree offered stunning support.

Stringer, Wilson, and other scientists began formulating a scenario for modern humans they called “Out of Africa.” As Homo spread out of Africa, they proposed, it evolved into several distinct species that did not breed with one other. Homo erectus settled across much of Asia, while Neanderthals (also known as Homo neanderthalensis, a species in its own right) established themselves in Europe and the Near East. During this time, Homo sapiens was evolving from older hominids back in Africa. At some point, Homo sapiens migrated to Asia and Europe. The cave paintings of Chauvet, as well as the jewelry, weapons, clothing, and other artifacts that turn up in the fossil record after 50,000 years ago were all made by Homo sapiens, who left them behind as they explored the world. And when Homo sapiens arrived on the territory of Homo erectus or Neanderthals, these other humans disappeared.

Although the Out of Africa hypothesis drew heavy fire when it was first proposed, it has been drawing strength from recent fossil discoveries in Asia, Europe, and Africa. Paleoanthropologists have found fossils of Neanderthals in Israel that lived alongside anatomically modern humans for 30,000 years without any sign of mixing before the Neanderthals disappeared. In Asia, Homo erectus survived long after Homo sapiens’s first fossils turned up. Some evidence suggests that Homo erectus was still alive as recently as 30,000 years ago on Java.

Meanwhile, discoveries in Africa have offered support of their own. “If we look at Europe 100,000 years ago,” says Richard Klein of Stanford University, “they’re exclusively Neanderthals. And then you look to Africa, and the people who were living in Africa are physically very modern in appearance.”

Geneticists who have followed up on Wilson’s initial work have generally confirmed the Out of Africa model. No matter which genes they analyze to construct the tree of human evolution, Africans consistently occupy branches that reach down closest to the base of the tree. With more sequences available to compare, mitochondrial genes now point to an origin 170,000 years ago. In the late 1990s, a team of geneticists compared the Y chromosomes of humans (the chromosome that determines whether a person is male). Those studies indicate that modern humans date back only 50,000 years. Of course, all the studies have a margin of error of tens of thousands of years, so they do not necessarily contradict one another.

These researchers will have to sort out who’s precisely right and who’s precisely wrong, but one thing is clear from all their work: we are a very young species.

Neanderthal DNA

If more proof was needed of our collective youth, the genes of Neanderthals can now provide it. In 1995 the German government asked Svante Pääbo, an expert on fossil DNA at the University of Munich, to see whether the original Neanderthal fossil found in 1856 still preserved any DNA. Pääbo was skeptical, since genes are so fragile, but he agreed to look. He and his graduate student Matthias Krings took a small sample of bone from the Neanderthal fossil’s upper arm and analyzed it for amino acids, the building blocks of proteins. They were surprised to find some, and they embarked on a search for genes. Where amino acids might still survive, they reasoned, DNA might survive as well.

The search was a difficult one, because even a speck of dust could contaminate the fossil with the DNA of living human beings. To eliminate the risk, Krings bleached the outside of the bone and then set up his equipment in a sterilized room. Only when he was sure he was free of contamination did he grind up the Neanderthal bone and apply chemicals that would copy any fragments of DNA it held.

Krings’s spine tingled as he watched the results come up on his computer: a sequence of 379 bases of DNA that was similar–but not identical–to human DNA. The champagne stayed corked, though, until the entire procedure was performed by researchers at the lab of Mark Stoneking at Penn State University on a second set of samples from the Neanderthal fossils. Stoneking independently discovered the same sequence.

Pääbo’s team then built an evolutionary tree by comparing the Neanderthal DNA to almost 1,000 sequences of human DNA, as well as the DNA of chimpanzees. On their tree, Europeans and Africans cluster together on one branch, while the Neanderthal belong to a completely separate branch. And judging by the number of differences that have accumulated between the genes of Neanderthals and Homo sapiens, Krings and his colleagues estimated that their common ancestor may have lived as long as 600,000 years ago. This common ancestor presumably lived in Africa; one branch of its descendants migrated into Europe and became Neanderthals. The one that stayed behind evolved into us.

When Pääbo’s team published their report in 1997, skeptics wondered if such a small fragment of Neanderthal DNA had enough information in it to put Neanderthals in their proper evolutionary place. But by 2000 two more pieces of Neanderthal DNA had come to light. Pääbo’s team discovered one of them in a set of 42,000‑year‑old bones from Croatia, while a separate team found genes in 29,000‑year‑old Neanderthal fossils from the Caucasus Mountains. In both cases, the scientists isolated the same stretch of DNA that Pääbo had discovered in the original Neanderthal material. The three sequences of DNA resembled one another much more than any of them resembled the genes of any living human. These genetic fragments came from Neanderthals separated from one another by hundreds of miles and thousands of years. The chances that they should all just happen to have such similar sequences is close to impossible.

The new evidence from Neanderthal DNA supports the hypothesis that Neanderthals went extinct. And yet the fossil record shows that Neanderthals were not a delicate species waiting to be nudged into oblivion. They were tough, resourceful humans, rugged enough to survive the ice ages of Europe. They made spears as elegantly balanced as Olympic javelins, which they used to kill horses and other big mammals. They were so good at hunting that their diet consisted almost entirely of meat. Neanderthals took care of their sick, as demonstrated by a skeleton from the Shanidar Cave in Iraq: it belongs to a man whose head and body had been smashed, yet who had lived for several more years.

Likewise, Homo erectus was not some hothouse flower of a hominid. Its range reached from the bleak northern edges of China to the sticky jungles of Indonesia, and in this domain it survived for well over a million years. And yet Homo sapiens is still here, while H. neanderthalensis and H. erectus are now gone. What was the difference that allowed us to survive?

A New Kind of Mind

The most obvious difference that paleoanthropologists can make out between modern humans 50,000 years ago and Homo erectus and Neanderthals is in the things that they made and left behind. Homo erectus in Asia never seems to have gotten beyond a hand‑axe level of technology. Neanderthals could make spears and a collection of stone blades, but little more.

Modern humans, on the other hand, invented new tools that demanded great skill to make, and invented them at an astonishing rate. Modern humans made spears tipped with antler–a lightweight but strong material that had to be soaked for hours and sanded down in order to make a point. They invented spear‑throwers that allowed them to flick their spears over their shoulders and hurl them much farther. Compared to Neanderthals, who charged their prey with wooden bayonets, modern humans could kill more game and put themselves at less risk in the process.

Not all of the inventions of modern humans were designed for practical purposes like hunting. In caves in Turkey, for example, scientists have found necklaces of snail shells and bird claws dating back at least 43,000 years. From the start, modern humans were wearing jewelry. It’s possible that these ornaments were a sort of tribal identification or a way people marked their rank in their band.

“People were investing thousands of hours of labor in the production of body ornaments,” says Randall White of New York University. “It was a priority in their lives, marking status and roles. When people put something on their bodies, it communicates immediately to other people who they are socially.”

The artifacts that humans left behind speak to a profound shift in the way humans saw themselves and the world. And that shift may have given them a competitive edge. “Something happened about 50,000 years ago,” explains Klein. “It happened in Africa. These people who already looked quite modern became behaviorally modern. They developed new kinds of artifacts, new ways of hunting and gathering, that allowed them to support much larger populations.”

Researchers can only speculate for now about what brought the shift about. Some have proposed that the creative revolution was purely a matter of culture. Anatomically modern humans in Africa experienced some change–perhaps a population boom–that forced their society to cross some kind of threshold. Under these new conditions, people invented modern tools and art. “Cro‑Magnons were perfectly capable of going to the moon neurologically, but they didn’t because they weren’t in a social context where the conditions were right,” says White. “There was no challenge to provoke that kind of invention.”

But Richard Klein, a paleoanthropologist at Stanford University, has grave doubts about such an explanation. If humans had the potential to paint the caves of Chauvet or build superior spears for hundreds of thousands of years, why was there such a long delay? If the revolution was purely cultural, then why didn’t the Neanderthals living side by side with modern humans for thousands of years adopt the new tools and art and make them their own, in the way today’s cultures borrow from one another?

Klein also points out that the ancestors of modern humans were probably not expanding their population when they suddenly changed their behavior. Geneticists can use the variability in the DNA of living humans to estimate how large their founding population was, and none of their estimates is very big. It now appears that all humans on the planet descend from just a few thousand Africans. “This emergence of fully modern humans appears to occur at a time when African populations were relatively sparse,” says Klein.

A small group may not be a good place for cultural changes to take place, but biologists have long known it can be good for evolutionary changes. Mutations can sweep through their ranks quickly, rapidly altering them in the process. And with that fact in mind, Klein has proposed that the dawn of modern humanity was brought about by biology. New mutations to the genes that shape the human brain cropped up in Africa 50,000 years ago and gave it the capacity to make art and technology–a capacity that no other earlier humans possessed. “My own view,” says Klein, “is that there was a brain change.”

That brain change might have allowed humans to escape the rigid mental constraints that had trapped their ancestors. Instead of viewing animals only as food, modern humans could also recognize that their bone and antlers could be used as tools. Instead of using the same weapons for all sorts of game, modern humans began to invent ones that were specialized for different kinds of game, be it fish or ibex or red deer. This new way of thinking–what Stephen Mithen, a University of Reading archaeologist, calls “fluid intelligence”–even allowed people to think abstractly about nature and themselves and create symbolic representations in the form of paintings and sculptures.

Language, at least in its fullest flower, might have also been part of this late‑blooming capacity. “It may be that what happened 50,000 years ago was the ability to produce speech rapidly, understandably, that other people could parse and make sense of; and then allow the use of that speech to spread information about new ways of doing things that people could not have spread in the same way before,” says Klein.

The complexity of the new technology was too great to learn simply by example. In Russia, people boiled mammoth tusks and then buried them with their dead. Such a tradition would be impossible for an inexpressive Neanderthal to carry on. Modern humans could describe their new inventions to other people, so that new ideas could spread quickly. Modern humans began making tools out of stone, ivory, and other materials that were transported hundreds of miles from their sources: language could have made it possible for bands to communicate with one another about the goods they wanted to trade. With language, modern humans could give particular meanings to jewelry and art, whether that meaning was social or sacred.

Researchers do not yet know exactly what happened when modern humans, equipped with a new culture and perhaps with new brains, emerged from Africa and began encountering Homo erectus and Neanderthals. Did they wage all‑out war? Did they bring devastating diseases to Europe and Asia, in the same way the Spanish brought smallpox to the Aztecs? Or perhaps, as many researchers suspect, the new brains of modern humans simply gave them a competitive edge. “They replaced Neanderthals in Europe principally because they were just behaving in a far more sophisticated way. And particularly, they were much more effective hunter‑gatherers,” says Klein.

Modern humans could trade with one another for supplies; they could use sophisticated language to settle disputes instead of spiraling into deadly battle. They could invent weapons and other tools to get more food and make clothes for themselves, and they could survive droughts and cruel winters that might have claimed other humans. The fossil evidence certainly suggests that they managed to live in higher densities than Neanderthals. The Neanderthals may have retreated to mountainous enclaves, where inbreeding and disasters eventually snuffed them out.

Not all modern humans headed into Europe, of course. The ones that spread into Asia may have hugged the coasts initially. Artifacts discovered along the Red Sea show that Africans had settled on its shores, living on shellfish, as early as 120,000 years ago. It’s possible that their descendants depended on this way of life as they colonized the coasts around the Arabian Peninsula and India and continued spreading toward Indonesia. When these troublesome newcomers arrived on the territory of Homo erectus, the resident hominids may have pulled back into the inland jungles to find refuge. Eventually they became so isolated that they winked out of existence 30,000 years ago. While some modern humans headed upriver into the heart of Asia, others set out to sea, using boats to get to New Guinea and Australia, where no hominid had ever set foot before. By 12,000 years ago humans had traveled from Asia to the New World, racing all the way to the southern tip of Chile. In an evolutionary flash, every major continent except for Antarctica was home to Homo sapiens. What had once been a minor subspecies of chimp, an exile from the forests, had taken over the world.