What does acceleration mean for evolutionary psychology?

The Newsweek a couple of weeks ago had a long (7 pages in the magazine!) essay/article titled, “Don’t Blame the Caveman”. Writer Sharon Begley sets out the thesis that evolutionary psychology is bad science.

If you haven’t been following Newsweek lately, you may not be aware that it’s not a news magazine anymore; it’s been transformed into a journal of opinion. I for one don’t like it. For one thing, a lot of people don’t follow science reporting, except for what they read in general newsmagazines. The old Newsweek tended to have one to three five-paragraph science stories every week, with a feature article about science (or health) every couple of months. The new Newsweek has had a couple of long-form opinion essays on science during the last four weeks, in addition to a one-page story and some columns by Begley. It ran a very good essay by Carl Zimmer on the reasons why it’s hard to find genes explaining the variance in risk for common disorders. On the other hand, last week’s issue on “What to Read” covered a lot of recent books, but hardly any about science. In terms of science coverage, the editorial change seems to have brought a reduction of breadth in exchange for some depth on the subjects covered.

Probably the sample is too small so far to make conclusions. But it seems to me, if you’re going to devote the resources of a national magazine to a long-form science essay every few weeks, why not get real scientists to write them? For instance, three weeks ago the magazine put out an issue guest-edited by Stephen Colbert. Putting aside the inherent lunacy of a news magazine edited by a parody artist, I had high hopes for this – Colbert’s program is one of the few general-interest television shows that does interviews with serious scientists (granted, they’re serious scientists who are all trying to promote their books….). But the Colbert-edited Newsweek got nobody and no science at all except for Sharon Begley’s column.

The evolutionary psychology essay featured Kim Hill and Elizabeth Cashdan as the “rational” voices of human behavioral ecology. So, gee, why not get one of them to write it? They’re both engaging writers with really interesting stories to tell. And either one of them would give a more balanced critique of evolutionary psychology’s excesses (and strengths).

The part where I come in

OK, enough about that. Begley’s essay raises several points that are worth discussing. The one that motivated me to start writing is that the essay mentions my research:

And for a final nail in the coffin, geneticists have discovered that human genes evolve much more quickly than anyone imagined when evolutionary psychology was invented, when everyone assumed that "modern" humans had DNA almost identical to that of people 50,000 years ago. Some genes seem to be only 10,000 years old, and some may be even younger (62).

It’s pretty cool that we’re now mainstream enough to show up in stories that seem unrelated (David Brooks also raised the issue in a NY Times op-ed). But is Begley right? Is the reality of recent human evolution a “nail in the coffin” for evolutionary psychology?

One thing is certain: we shouldn’t assume that human minds are “adapted to the Stone Age.” I can’t take credit for this – the fact of Holocene human evolution has been well documented for more than a hundred years! Besides that, anybody who knows a smattering of genetics (say, the breeder’s equation) would know how silly it is to claim that human behaviors couldn’t in principle have recently changed under selection.

Now, the question is how much would selection have influenced human behavioral phenotypes during the last 30,000 years or so? Could it have changed us into radically different creatures? Would it make us unfit for Pleistocene life?

Short answer: It’s impossible yet to generalize.

I’ve taken a while to write up this little post, because I think it’s a very important problem, and the answer isn’t obvious (at least, to me). We know that some radical phenotypic changes have happened in human populations during the last 30,000 years. Some pseudogene-making mutations – like the Duffy null allele, or the truncated allele of caspase-12 – have gone to near fixation in one or more populations. That’s a shallow genetic change – it only takes one mutation to have a large fitness effect.

How likely are behavioral phenotypes to be improved by such shallow changes? Domestication of animals seems to show that it’s possible to effect big changes in behavior in a similar timespan, given standing variation and relatively simple genetic changes. Even so, we might guess that humans are different from domesticates. Human populations have been subject to conflicting behavioral demands, making directional selection for tameness a questionable model.

Meanwhile, human learning depends on neural plasticity. As the environment changes, humans can adjust many of their behavioral phenotypes by learning from the novel environments. This plasticity might take the sharp edge off of fitness differentials among individuals, reducing the strength of selection on the genes that influence behavior. Or rapid environmental change might select for plasticity itself – changing the facility of learning, without necessarily changing any outcomes that are observable from archaeological sources. All this means that it’s not obvious whether I can form any simple, general answer to the question.

I am a little hopeful, though, because it seems to me that we have to answer the same questions with evolutionary psychology in general. Holocene evolution isn’t different from Pleistocene evolution, except to the extent that Holocene conditions were different. If we ask “How would humans adapt to large, sedentary populations?” it’s the same kind of question as “How would humans adapt to small band-sized groups?” and ought to involve the same evolutionary mechanisms.

The question bears much more consideration than I can give in this short post. I have a raft of notes already from the last couple of weeks it’s been percolating on my stack. So while I’m out of town this week I’ll see if I can pull those thoughts together into a more coherent form.