Why the West Rules--For Now (12 page)

Clarke set his
2001
moment 3 million years ago, presumably to account for the invention of tools by
Homo habilis
, but I always felt that the place where a good monolith would really do some work was when fully modern humans appeared. By the time I started studying archaeology in college I had learned not to say things like that, but I couldn’t shake the feeling that the professionals’ explanations were less compelling than Clarke’s.

The big problem archaeologists had in those far-off days when I was an undergraduate was that they simply had not excavated very many sites dating between 200,000 and 50,000 years ago. As new finds accumulated across the 1990s, though, it began to become clear that we did not need monoliths after all; in fact, the Great Leap Forward itself began to dissolve into a series of Baby Steps Forward, spread across tens of thousands of years.

We now know of several pre-50,000-
BCE
sites with signs of surprisingly modern-looking behavior. Take, for instance, Pinnacle Point, a cave excavated in 2007 on the South African coast.
Homo sapiens
moved in here about 160,000 years ago. This is interesting in itself: earlier ape-men generally ignored coastal sites, probably because they could not work out how to find much food there. Yet
Homo sapiens
not only
headed for the beach—distinctly modern behavior—but when they got there they were smart enough to gather, open, and cook shellfish. They also chipped stones into the small, light points that archaeologists call bladelets, perfect as tips for javelins or arrows—something that neither Peking Man nor Europe’s Neanderthals ever did.

On a handful of other African sites people engaged in different but equally modern-looking activity. About a hundred thousand years ago at Mumbwa Cave in Zambia people lined a group of hearths with stone slabs to make a cozy nook where it is easy to imagine them sitting around telling stories, and at dozens of sites around Africa’s coasts, from its southern tip to Morocco and Algeria in the north (and even just outside Africa, in Israel), people were sitting down and patiently cutting and grinding ostrich eggshells into beads, some of them just a quarter of an inch across. By ninety thousand years ago people at Katanda in the Congo had turned into proper fishermen, carving harpoons out of bone. The most interesting site of all, though, is Blombos Cave on Africa’s southern coast, where in addition to shell beads, excavators found a 77,000-year-old stick of ocher (a type of iron ore). Ocher can be used for sticking things together, waterproofing sails, and all kinds of other tasks; but in recent times it has been particularly popular for drawing, producing satisfyingly bold red lines on tree bark, cave walls, and people’s bodies. Fifty-seven pieces turned up at Pinnacle Point, and by 100,000
BCE
it shows up on most African sites, which probably means that early humans liked drawing. The truly remarkable thing about the Blombos ocher stick, though, is that someone had scratched a geometric pattern on it, making it the world’s oldest indisputable work of art—and one made for producing more works of art.

At each of these sites we find traces of one or two kinds of modern behavior, but never of the whole suite of activities that becomes familiar after 50,000
BCE
. Nor is there much sign yet that the modern-looking activities were cumulative, building up gradually until they took over. But archaeologists are already beginning to feel their way toward an explanation for the apparent baby steps toward fully modern humanity, driven largely by climate change.

Geologists realized back in the 1830s that the miles-long, curving lines of rubble found in parts of Europe and North America must have been created by ice sheets pushing debris before them (not, as had previously been thought, by the biblical flood). The concept of an “ice
age” was born, although another fifty years passed before scientists understood exactly why ice ages happen.

Earth’s orbit around the sun is not perfectly round, because the gravity of other planets also pulls on us. Over the course of a hundred thousand years our orbit goes from being almost circular (as it is now) to being much more elliptical, then back again. Earth’s tilt on its axis also shifts, on a 22,000-year rhythm, as does the way the planet wobbles around this axis, this time on a 41,000-year scale. Scientists call these Milankovich cycles, after a Serbian mathematician who worked them out, longhand, while interned during World War I (this was a very gentlemanly internment, leaving Milankovich free to spend all day in the library of the Hungarian Academy of Sciences). The patterns combine and recombine in bewilderingly complex ways, but on a roughly hundred-thousand-year schedule they take us from receiving slightly more solar radiation than the average, distributed slightly unevenly across the year, to receiving slightly less sunlight, distributed slightly more evenly.

None of this would matter much except for the way Milankovich cycles interact with two geological trends. First, over the last 50 million years continental drift has pushed most land north of the equator, and having one hemisphere mostly land and the other mostly water amplifies the effects of seasonal variations in solar radiation. Second, volcanic activity has declined across the same period. There is (for the time being) less carbon dioxide in our atmosphere than there was in the age of the dinosaurs, and because of this the planet has—over the very long run and until very recently—steadily cooled.

Through most of Earth’s history the winters were cold enough that it snowed at the poles and this snow froze, but normally the sun melted this ice every summer. By 14 million years ago, however, declining volcanic activity had cooled Earth so much that at the South Pole, where there is a large landmass, the summer sun no longer melted the ice. At the North Pole, where there is no landmass, ice melts more easily, but by 2.75 million years ago temperatures had dropped enough for ice to survive year-round there, too. This had huge consequences, because now whenever Milankovich cycles gave Earth less solar radiation, distributed more evenly across the year, the North Pole ice cap would expand onto northern Europe, Asia, and America, locking up more water, making the earth drier and the sea level lower, reflecting back more solar radiation, and reducing temperatures further still. Earth then spiraled down
into an ice age—until the planet wobbled, tilted, and rotated its way back to a warmer place, and the ice retreated.

Depending on how you count, there have been between forty and fifty ice ages, and the two that spanned the period from 190,000 through 90,000
BCE
—crucial millennia in human evolution—were particularly harsh. Lake Malawi, for instance, contained just one-twentieth as much water in 135,000
BCE
as it does today. The tougher environment must have changed the rules for staying alive, which may explain why mutations favoring braininess began flourishing. It may also explain why we have found so few sites from this period; most protohumans probably died out. Some archaeologists and geneticists in fact estimate that around 100,000
BCE
there were barely twenty thousand
Homo sapiens
left alive.

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.