Apparently it predicts intelligence:
body symmetry more strongly predicts intelligence than brain size, nerve conduction velocity, reaction time reliability, and a number of other measures.
And the point:
The authors suggest that human intelligence may therefore be a “fitness indicator,” like a male peacock’s tail is a sexual advertisement to female peacocks.
Here’s another interesting sentence:
Bodily symmetry may reflect “developmental stability” – i.e., influences like disease, mutation and stress may cause a developmental divergence from DNA’s symmetric blueprint.
(Symmetric blueprint, eh? So nurture wins?)
Now, do I know anything about brain science or evolutionary biology? Absolutely not.
I do know that the measures of intelligence they used (two vocabulary tests and a pattern recognition test), don’t quite nail what I’d call genuine General Intelligence.
Let me put it this way: prospective mates don’t give each other math tests and actually using the vocabulary you’d surely need to ace the “WAIS II vocabulary quiz” could well be a countra-signal of mating fitness (ie being a dorky ‘try-hard’).
These are proxies for intelligence, of course, but not the proxies real people use. For real people, general intelligence is signaled through humor, social facility and (messily) through brute force financial might.
I’m not arguing against the conclusion, nor indeed against the hypothesis. It rings true. I just get the impression that ‘academics’ like to think ‘book smarts’ matters in a direct evolutionary sense. I don’t think it does.
It’s a byproduct. These studies work because intelligence developed for one thing bleeds over into everything else.
Robin Hanson gets it (obviously):
an “intelligent” thing has a great many useful capabilities, not some particular specific capability called “intelligence.”