How We Evolve

How We Evolve

by Benjamin Phelan

When the previous generation of life scientists was coming up through the academy, there was a widespread assumption, not always articulated by professors, that human evolution had all but stopped. It had certainly shaped our prehuman ancestors — Auralopithecus, Paranthropus, and the rest of the ape-men and man-apes in our bushy lineage — but once Homo sapiens developed agriculture and language, it was thought, we stopped changing. It was as though, having achieved its aim by the seventh day, evolution rested. "That was the stereotype that I learned," says population geneticist and anthropologist Henry Harpending. "We showed up 45,000 years ago and haven't changed since then."

The idea makes a rough-and-ready kind of sense. Natural selection derives its power to transform from the survival of some and the demise of others, and from differential reproductive success. But we nurse our sick back to health, and mating is no longer a privilege that males beat each other senseless to secure. As a result, even the less fit get to pass on their genes. Promiscuity and sperm competition have given way to spiritual love; the fittest and the unfit are treated as equals, and equally flourish. With the advent of culture and our fine sensibilities, the assumption was, natural selection went by the board.

Moreover, evolution had never been observed in humans, except in a few odd cases, so the conclusion was drawn that it wasn't happening. One can't fault the logic. The most famous case of adaptive change in humans, that of sickle cell trait as an evolutionary response to malaria, seemed to prove the point that human evolution must be rare: Even in as dire and malaria-stricken an environment as West Africa, the only response evolution has been able to come up with is an imperfect defense that can cause serious health problems along with its solitary benefit. Selection pressures as strong as those brought about by endemic malaria are uncommon, and civilization was thought to wash out those less powerful.

But since the turn of the millennium, genomics has undergone a revolution. With the completion of such landmark studies as the Human Genome Project and the publication of HapMap, scientists finally have access to the particles of evolution. They can inspect vast stretches of DNA from people of all ethnicities, and the colossal amount of information suddenly available has spurred a revision of the old static picture that will render it unrecognizable. Harpending and a host of researchers have discovered in our DNA evidence that culture, far from halting evolution, appears to accelerate it.

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