So much evolution, so little time

The Society’s April book is Before the Dawn by Nicholas Wade, the NYT science writer. He gives a précis of what science – especially genetics – has learned in the last ten years about recent human evolution. He quotes extensively from Charles Darwin at the top of each chapter, but I have to say that in a way, the story Wade tells makes me sympathize with the creationists. It is a hard story to get your head around.

He tells a riveting tale: that the human family as we know it is only 50,000 years old. That about that time, a group 1/5th the size of my graduating class at West High School ‘65 - maybe 150 people - from the ancestral population in NW Africa crossed the Red Sea and – to make a long story short – populated the world. (Presumably, their cousins who stayed behind populated Africa.) There were older hominids around like Neanderthal and H. erectus, but Wade avers they lacked that special something, maybe language, to make them fully human. Humans may have looked modern for 100,000 years or more, but the new population was “behaviorally modern,” which is to say they lived like modern hunter-gatherer societies.

We are used to thinking of evolution in millions of years. The time of the glaciers is recent history, at least in geologic time. But Wade postulates that human intelligence, language, pacific behavior, races and many other sine qua nons of humanity evolved quickly, and in some cases, multiple times in the space of only a few hundred generations. In his words:

Human behavior, whether in the search for reproductive advantage or the defense of territory, shows a clear continuity with that of apes. But it also developed its own characteristic pattern with two pivotal steps: the emergence of long-lasting bonds between men and women some 1.7 million years ago, and at 50,000 years ago, the evolution of language. Language opened the door to a new level of social interaction. Early human groups developed the institutions that shape even the largest and most sophisticated of today’s urban societies. These included organized warfare; reciprocity and altruism; exchange and trade; and religion. All were present in embryo form in the hunter-gatherer societies of the upper Paleolithic. But it required another development, a diminution of human aggression and probably the evolution of new cognitive faculties, for the first settlements to emerge, beginning 15,000 years ago, and it was in the context of settled societies that warfare, trade and religion attained new degrees of complexity and refinement.

The relentless search for new solutions produced not one, but a whole clutch of hominid species. At least three: the Neanderthals, Homo erectus, and Homo floresiensis, (all descended from the earlier lines of humanity) survived until modern humans made their exit from Africa. Had these archaic people endured till the present day, our own species would surly seem less special, being evidently just one of many ways in which evolution could spin variations out of the basic ape lineage.

The evidence now accumulating from the genome establishes that human evolution has continued throughout the last 50,000 years. The recent past, especially since the first settlements 15,000 years ago, is a time when human society has undergone extraordinary developments in complexity, creating many new environments and evolutionary pressures. Hitherto it has been assumed that the human genome was fixed and could not respond to those pressures. It now appears the opposite is the case.