Greg Cochran over at West Hunter has a pretty damning critique of this paper.
In two recent papers, Gerald Crabtree says two correct things. He says that the brain is complex, depends on the correct functioning of many genes, and is thus particularly vulnerable to genetic load. Although he doesn’t use the phrase “genetic load”, probably because he’s never heard it. He goes on to say that that this is not his area of expertise: truer words were never spoken!
His general argument is that selection for intelligence relaxed with the development of agriculture, and that brain function, easier to mess up than anything else, has probably been deteriorating for thousands of years. We are dumber than out ancestors, who were dumber than theirs, etc.
The first bit, about the relaxation of selection for intelligence in the Neolithic -. Sure. As we all know, just as soon as people domesticated emmer wheat, social workers fanned out, kept people from cheating or killing their neighbors, and made sure that fuckups wouldn’t starve to death. Riiight -it’s all in the Epic of Gilgamesh. In the online supplement.
Why do people project a caricature of modernity back thousands of years before it came into existence? Man, he doesn’t know much about history.
Nor does he know much about biology. If he did, he’d understand that truncation selection is what makes such complex adaptations possible. If only the top 85% (in terms of genetic load) reproduce, the average loser has something like 1 std more load , so each one takes lots of deleterious mutations with him. But then, he’s probably never heard of truncation selection. I’m sure they never taught him that in school, but that’s no excuse – they never taught me, either.
If his thesis was correct, you’d expect hunter-gatherers to be smarter than people from more sophisticated civilizations, which is the crap that Jared Diamond peddles about PNG. But Crabtree says that everyone’s the same – stepping on the dick of his own argument. Of course, in reality, hunter-gatherers score low, often abysmally low, and have terrible trouble trying to fit in to more complex civilizations. They do a perfect imitation of being not-smart, amply documented in the psychometric literature. Of course, he doesn’t know anything about those psychometric results.
Which reminds me of secret clearances: it used to be that having a clearance mean that you were entrusted with information that most people didn’t have. Now, it means that you can’t read Wikileaks, even though everyone else does. In much the same way, you may have the silly impression that having a Ph.D. means knowing more than regular people – but in the human sciences, the most important prerequisite is not knowing certain facts. Some kind soul should post the Index, so newbies won’t get themselves in trouble.
He doesn’t even know things that would almost support his case. Average brain size has indeed decreased over the Neolithic- but in every population, not just in farmers. He might talk about paternal age effects, and how average paternal age varies – but he doesn’t know anything about it. He ought to be thinking about the big population increase associated with agriculture, and the ensuing Fisherian acceleration – but he’s never heard of it.
He even gets the peripheral issues wrong. He talks about language as new, 50,000 years old or so – much more recent than the split between Bushmen/Pygmies and the rest of the human race. Yet they talk. He says that the X chromosome isn’t enriched for cognition and behavioral genes – but it is (by at least a factor of two) , and the reference he quotes confirms it.
Selection pressures and mutation rates can vary in space and time. Intelligence could decrease – it’s not impossible. But we know that the pattern he suggests does not exist. Or, to be exact, in exists only in that neighboring world that’s full of Melanesian super-hackers, gay men whose main concern is avuncular investment, and butt-kicking pixies.