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 sooften, 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 colonistsmoved 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.
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 sooften, 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 colonistsmoved 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.
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