by Morris, Ian;
If this new theory is correct, the population crisis would have done several things at once. On the one hand, by shrinking the gene pool it would have made it easier for mutations to flourish; but on the other, if Homo sapiens bands became smaller they would die out more easily, taking any advantageous mutations with them. If (as seems likely from the tiny number of sites known from this period) there were also fewer bands, groups would meet less often and have less chance to pool their genes and knowledge. We should probably imagine that for a hundred thousand years tiny bands of protohumans eked out livings in Africa in unfriendly and unpredictable environments. They did not meet, interbreed, or exchange goods and information very often. Genetic mutations flourished in these isolated pockets of people, some producing humans very like us, some not. Some groups figured out harpoons, many made beads, but most did neither, and the specter of extinction haunted them all.
These were dark days for Homo sapiens, but around seventy thousand years ago their luck changed. Eastern and southern Africa became warmer and wetter, which made hunting and gathering easier, and humans reproduced as rapidly as their food sources. Modern Homo sapiens had been evolving for a good hundred thousand years, with a lot of trial, error, and extinctions, but when the climate improved, those populations with the most advantageous mutations took off, outbreeding less brainy humans. There were no monoliths; no Great Leap Forward; just a lot of sex and babies.
Within a few thousand years early humans reached a tipping point that was as much demographic as biological. Instead of dying out so often, bands of modern humans grew big enough and numerous enough to stay in regular contact, pooling their genes and know-how. Change became cumulative and the behavior of Homo sapiens diverged rapidly from that of other ape-men. And once that happened, the days of biological distinctions between East and West were numbered.
OUT OF AFRICA—AGAIN
Figure 1.3. The unity of mankind restored: the spread of fully modern humans out of Africa between roughly 60,000 and 12,000 years ago. The numbers show how many years ago humans arrived in each part of the world and the coastlines represent those of the late Ice Age, around 20,000 years ago.
Climate change is rarely simple, and while Homo sapiens’ homelands in eastern and southern Africa were getting wetter seventy thousand years ago, North Africa was drying out. Our ancestors, multiplying rapidly in their home ranges, chose not to spread in that direction; instead, little bands wandered from what is now Somalia across a land bridge to southern Arabia, and then to Iran (Figure 1.3). At least, this is what we think they must have done. There has been relatively little archaeological exploration in South Asia, but we have to assume bands of modern humans moved this way, because by 60,000 BCE they had reached Indonesia, taken to boats, crossed fifty miles of open water, and wandered as far as Lake Mungo in southern Australia. The colonists moved fifty times faster than Homo erectus/ergaster had done when they left Africa, averaging more than a mile a year compared to the earlier ape-men’s thirty-five yards.
Between fifty thousand and forty thousand years ago a second wave of migrants probably moved through Egypt into southwest and central Asia, spreading from there into Europe. Clever enough to make themselves delicate blades and bone needles, these modern humans cut and sewed fitted clothing and built houses out of mammoth tusks and skins, turning even the frigid wastes of Siberia into a home. Around 15,000 BCE humans crossed the land bridge linking Siberia and Alaska and/or sailed in short hops along its edge. By 12,000 BCE they had left coprolites (scientist-speak for dung) in caves in Oregon and seaweed in the mountains of Chile. (Some archaeologists think humans also crossed the Atlantic along the edge of ice sheets then linking Europe and America, though as yet this remains speculative.)
The situation in East Asia is less clear. A fully modern human skull from Liujiang in China may be 68,000 years old, but there are some technical problems with this date, and the oldest uncontroversial remains date back only to around 40,000 BCE. More digging will settle whether modern humans reached China relatively early or relatively late,* but they certainly reached Japan by twenty thousand years ago.
Wherever the new humans went, they seem to have wrought havoc. The continents where earlier ape-men had never set foot were teeming with giant game when Homo sapiens arrived. The first humans to enter New Guinea and Australia encountered four-hundred-pound flightless birds and one-ton lizards; by 35,000 BCE these were extinct. The finds from Lake Mungo and a few other sites suggest that humans arrived around 60,000 BCE, meaning that humans and megafauna coexisted for twenty-five millennia, but some archaeologists dispute the dates, putting humanity’s arrival just forty thousand years ago. If they are right, the great beasts disappeared suspiciously quickly after humans arrived. In the Americas, the first human colonists fifteen thousand years ago met camels, elephants, and huge ground sloths; within four thousand years these, too, were all extinct. The coincidence between the coming of Homo sapiens and the going of the giant animals is, to say the least, striking.
There is no direct evidence that humans hunted these animals to extinction or drove them off their ranges, and alternative explanations for the extinctions (like climate change or comet explosions) abound. But there is less debate over the fact that when modern humans entered environments already occupied by ape-men, the ape-men became extinct. Modern humans had entered Europe by 35,000 BCE, and within ten thousand years Neanderthals had vanished everywhere except the continent’s mountainous fringes. The latest Neanderthal deposits known to us, from Gibraltar in southern Spain, date to around 25,000 BCE. After dominating Europe for 150,000 years, the Neanderthals simply disappeared.
The details of how modern humans replaced ape-men, though, are crucial for deciding whether racial explanations for Western rule make sense. We do not know, yet, whether our ancestors actively killed less intellectually gifted species or just outcompeted them for food. At most sites, modern human deposits simply replace those associated with Neanderthals, suggesting that the change was sudden. The main exception is Reindeer Cave in France, where phases of Neanderthal and modern human occupation apparently alternated between 33,000 and 35,000 years ago, and the Neanderthal layers contain stone foundations for huts, bone tools, and necklaces of animal teeth. The excavators suggested that Neanderthals learned from modern humans and were moving toward a Dawn of Neanderthal Consciousness. Several finds of ocher on Neanderthal sites in France (twenty pounds of it in one cave) may point the same way.
It is easy to imagine heavily muscled, low-browed Neanderthals watching the quicker, talkative newcomers painting their bodies and building huts, then struggling to repeat these actions with their clumsy fingers, or perhaps trading freshly killed meat for jewelry. In The Clan of the Cave Bear, Jean Auel imagined modern humans contemptuously chasing off Neanderthal “Flatheads,” while Neanderthals just tried to stay out of the way of “the Others”—except, that is, for Ayla, an orphaned five-year-old human girl whom the Neanderthal Cave Bear clan adopt, with transformative results. It is all fantasy, of course, but it is as plausible as anyone else’s guess (unless we follow those unromantic archaeologists who point out that sloppy excavation is the most economical explanation for the interleaved Neanderthal and human deposits at Reindeer Cave, meaning that there is no direct evidence for Flatheads learning from Others).
The bottom line is sex. If modern humans replaced Neanderthals in the Western Old World and Homo erectus in the Eastern regions without interbreeding, racist theories tracing contemporary Western rule back to prehistoric biological differences must be wrong. But was that what happened?
In the heyday of so-called scientific racism in the 1930s, some physical anthropologists insisted that modern Chinese people were more primitive than Europeans because their skulls had similarities (small ridges on top, relatively flat upper faces, nonprotruding jaws, shovel-shaped incisors) to those of Peking Man. So, too, these anthropologists pointed out, the skulls of Australia’s indigenous peoples had similarities—ridges around the
back for attaching neck muscles, shelflike brows, receding foreheads, large teeth—with those of Indonesian Homo erectus a million years ago. Modern Easterners, these (Western) scholars concluded, must have descended from these more primitive ape-men, while Westerners descended from the more advanced Neanderthals; and that might well explain why the West rules.
No one puts things so crudely today, but if we are serious about asking why the West rules we have to confront the possibility that Homo sapiens interbred with premodern peoples, and that Eastern populations remain biologically less advanced than Western. We will never be able to excavate copulating cavemen to see whether Homo sapiens merged their genes with Neanderthals in the West and with Peking Man in the East, but fortunately we do not need to, because we can observe the consequences of their trysts in our own bodies.
Each of us has inherited our DNA from all the ancestors we ever had, which means that in theory geneticists could compare the DNA of everyone alive and draw a family tree going back to humanity’s most recent shared ancestor. In practice, though, the fact that half the DNA in your body comes from your mother’s line and half from your father’s makes disentangling the information as difficult as unscrambling an egg.
Geneticists found a clever way around this problem by focusing on mitochondrial DNA. Rather than being reproduced sexually, like most DNA, mitochondrial DNA is transmitted solely by women (men inherit mitochondrial DNA from their mothers but do not pass it on). Once upon a time we all had the same mitochondrial DNA, so any difference between the mitochondrial DNA in my body and that in yours must be the result of random mutations, not sexual mixing.
In 1987 a team led by the geneticist Rebecca Cann published a study of mitochondrial DNA in living people from all over the world. They distinguished about 150 types within their data and realized that no matter how they shuffled the statistics, they kept getting three key results: first, that there is more genetic diversity in Africa than anywhere else; second, that the diversity in the rest of the world is just a subset of the diversity within Africa; and third, that the deepest—and therefore oldest—mitochondrial DNA lineages all come from Africa. The conclusion was unavoidable: the last female ancestor shared by everyone in the world must have lived in Africa—African Eve, as she was immediately dubbed. As Cann and her colleagues observed, she was “one lucky mother.” Using standard estimates of mutation rates in mitochondrial DNA, they concluded that Eve lived 200,000 years ago.
Throughout the 1990s paleoanthropologists argued over the Cann team’s conclusions. Some questioned their methods (there are thousands of ways to arrange the scores, in theory all equally valid) and others their evidence (most of the “Africans” in the original study were actually African-Americans), but no matter who redid the samples or the numbers, the results came out much the same. The only real change was to push Eve’s lifetime closer to 150,000 years ago. To clinch matters, African Eve got company at the end of the 1990s when technical advances allowed geneticists to examine nuclear DNA on the Y chromosome. Like mitochondrial DNA, this is reproduced asexually, but is transmitted only through the male line. The studies found that Y-chromosome DNA also has the greatest variety and deepest lineages in Africa, pointing to an African Adam living between sixty thousand and ninety thousand years ago, and an origin for non-African variants around fifty thousand years ago.* In 2010, geneticists added one more detail: immediately after they left Africa, Homo sapiens copulated enough with Neanderthals to pick up a trace of their DNA, and they then spread this mix across the rest of the planet.
But some paleoanthropologists remain unconvinced, insisting that genetics counts for less than the skeletal similarities they see between Western Homo sapiens and Neanderthals and between Eastern Homo sapiens and Homo erectus. In place of the out-of-Africa model they propose a “multiregional” model. Maybe, they concede, the initial Baby Steps Forward did happen in Africa, but population movements between Africa, Europe, and Asia then promoted such rapid gene flows that beneficial mutations in one place spread everywhere within a few thousand years. As a result, slightly different kinds of modern humans evolved in parallel in several parts of the world. That would explain both the skeletal and the genetic evidence, and would also mean that Easterners and Westerners really are biologically different.
Like so many theories, multiregionalism can cut two ways, and some Chinese scientists have insisted that China is exceptional beause—as the China Daily newspaper puts it—“modern Chinese man originated in what is present-day Chinese territory rather than Africa.” Since the late 1990s, though, the evidence has tipped steadily against this idea. There has been relatively little analysis of ancient DNA in East Asia, and still less that offers cheer to the multiregionalists. The authors of one Y-chromosome study even conclude that “the data do not support even a minimal in situ hominid contribution to the origin of anatomically modern humans in East Asia.” In Europe, initial studies of Neanderthal mitochondrial DNA found zero overlap with human mitochondrial DNA (whether found in 24,000-year-old skeletons or in living, breathing Europeans), suggesting that Neanderthals and Homo sapiens did not—perhaps could not—interbreed at all. The unraveling of the full Neanderthal genome has now shown that this went too far, and that Neanderthals did once inspire enough passion among Homo sapiens to make a small mark on our DNA; but it also showed that that mark is exactly the same all the way from France to China. Everywhere in Eurasia, people (in large groups) are all much the same.
The debate over multiregional origins drags on, and as recently as 2007 new finds from Zhoukoudian and from Xuchang were being trumpeted as showing that modern humans must have evolved from Homo erectus in China. Even as the publication announcing these finds was being printed, however, other scholars drove what looks to be the final nail into the multiregionalist coffin. Their sophisticated multiple-regression analysis of measurements from more than six thousand skulls showed that when we control for climate, the variations in skull types around the world are in fact consistent with the DNA evidence. Our dispersals out of Africa in the last sixty thousand years wiped the slate clean of all the genetic differences that had emerged over the previous half million years.
Racist theories grounding Western rule in biology have no basis in fact. People, in large groups, are much the same wherever we find them, and we have all inherited the same restless, inventive minds from our African ancestors. Biology by itself cannot explain why the West rules.
PREHISTORIC PICASSOS
So if the racial theories are wrong, where did East and West begin? The answer has seemed obvious to many Europeans for more than a hundred years: even if biology does not enter into it, they have confidently asserted, Europeans have just been culturally superior to Easterners ever since there were such things as modern humans. The evidence that convinced them began to appear in 1879. Charles Darwin’s On the Origin of Species, published two decades earlier, had made fossil-hunting a respectable hobby for gentlemen, and like so many of his class, Don Marcelino Sanz de Sautuola took to looking for cavemen on his estates in northern Spain. One day, with his daughter in tow, he visited the cave of Altamira. Archaeology is not much fun for eight-year-olds, so while Sautuola fixed his eyes on the ground, little Maria ran around playing games. “Suddenly,” she told an interviewer many years later, “I made out forms and figures on the roof.” She gasped: “Look, Papa, bulls!”
All archaeologists dream of an “Oh my God” moment—the instant of absolute disbelief, when time stands still and everything falls away in the face of the unbelievable, awe-inspiring discovery. Not many archaeologists actually have one, and maybe no archaeologist ever had one quite like this. Sautuola saw bison, deer, layer upon layer of multicolored animals covering twenty feet of the cave’s ceiling, some curled up, some cavorting, some leaping gaily (Figure 1.4). Each was beautifully, movingly rendered. When Picasso visited the site years later, he was stunned. “None of us could paint like that,” he said. “After Altamira, all is decadence.”
Figu
re 1.4. “After Altamira, all is decadence …” Just part of the stunning Ceiling of Bulls discovered by eight-year-old Maria Sanz de Sautuola in 1879, which ruined her father’s life and took Picasso’s breath away.
Sautuola’s first reaction was to laugh, but quickly he became “so enthusiastic,” Maria recalled, “that he could hardly speak.” He gradually convinced himself that the paintings really were ancient (the latest studies suggest some are more than 25,000 years old). Back in 1879, though, no one knew this. In fact, when Sautuola presented the site at the International Congress of Anthropology and Prehistoric Archaeology in Lisbon in 1880, the professionals laughed him off the stage. Everyone knew that cavemen could not produce such art; Sautuola, they agreed, was either a liar or a sucker. Sautuola took this—rightly—as an attack on his honor. He died a broken man eight years later. His “Oh my God” moment ruined his life.
Not until 1902 did Sautuola’s main critic actually visit Altamira and publicly recant, and since then several hundred prehistoric painted caves have been found. Chauvet Cave in France, one of the most spectacular of all, was discovered as recently as 1994, so well preserved that it looked like the artists had just stepped out for a quick bite of reindeer and would be back at any moment. One of the paintings at Chauvet is thirty thousand years old, making it one of the earliest traces of modern humans in western Europe.