• November 22, 2014

Fast Evolution

For the 10th-anniversary issue of The Chronicle Review, we asked scholars and illustrators to answer this question: What will be the defining idea of the coming decade, and why?

The Human Genome Project failed to deliver what it promised—a code book in which we could identify the genes responsible for many diseases. But the reason for this failure is itself a major discovery: The genome is far more dynamic and variable than we thought. Gene activity varies within each person, across the life span, and in response to changing environments. Genes vary at high levels across people, ethnic groups, and eras. This is big news, and I predict that it's going to rock many boats, in many academic departments.

When I was in graduate school in the 1990s, the prevailing view was that evolution was so slow that there could be no meaningful genetic differences among human groups. The genetic "blueprint" was assumed to have been finalized during the Pleistocene era, the two million years during which our ancestors lived as relatively egalitarian bands of hunter-gatherers. Modern humans all draw cards from the same deck, the same population of genes, except for some trivial variations related to adaptations for cold weather (such as lighter skin and smaller noses).

But now that we can examine partial genetic maps from thousands of people around the world, the old view is crumbling. Genetic evolution is not slow, and it certainly did not stop around 50,000 years ago, when people began leaving Africa and filling every continent save Antarctica. In fact, it now appears that the human diaspora greatly increased the pace of genetic change. When people exposed themselves to new climates, pathogens, diets, technologies, and social structures, they exposed their genes to new selection pressures. You don't need 50 millennia to get big changes. Some Russian fox breeders created what was essentially a new species of tame, doglike foxes in just 30 generations.

Over the next 10 years, therefore, we'll be hearing less about the Pleistocene and more about the Holocene—the 12,000 years since the beginning of agriculture. We've accepted findings that some ethnic groups adapted during the Holocene to digest milk as adults or to breathe more easily at high altitudes. But what will happen when findings come in about personality traits? Nearly all traits are heritable, and some traits surely paid off more handsomely in commercial cultures than in agricultural ones, or on peaceful islands than on raid-prone steppes. Such findings will be among the greatest threats to political correctness ever to emerge from the natural sciences.

The good news is that because evolution is so fast we'll stop talking about continentwide "races." We'll be looking at smaller groups that shared sustained selection pressures for dozens of generations or more. Also, the differences across groups are sure to be small when compared with the large variations found within every group. And finally, any recently selected traits were selected because they were strengths in their original contexts, so future talk about genetic variation might be productively assimilated into our current discourse about diversity, rather than forcing us to replay The Bell Curve controversies of the 1990s. But whichever way it goes, we'll be talking about fast evolution for the rest of the decade.

Jonathan Haidt is a professor of psychology at the University of Virginia.

Comments

1. gahnett - September 01, 2010 at 07:20 pm

yikes, this is really bad.

2. virgilr - September 02, 2010 at 08:26 pm

For some traits subject to very recent selection pressure, much of the variation will be, as Haidt suggests, unique to particular local populations. Yet there are clearly also traits for which large geographically isolated populations (i.e. the classically defined major races) have gradually diverged. The fact we have yet to find common variations responsible even for the heritable individual differences already well documented by behavior geneticists (such as for height, personality, disease risk etc.) does not mean, as generally assumed, that this variation must consist entirely of large numbers of low frequency polymorphisms. In fact, it may be that little of this variation is caused by single nucleotide polymorphisms at all, even though this has been the primary target of our search. Differences in the number of copies of entire DNA segments, (even entire genes) now appear to be a larger source of biologically significant within species variation. Correlations between these “copy number variations” (which are just now being systematically documented) and differences in important behavioral traits, may be the primary source of the politically explosive findings Haidt predicts.

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