> mme_n_b and others point out that if there were a latitude-IQ correlation, we would expect people who adapted for cold climates to be at some sort of mental disadvantage in warm climates, and there's not a lot of great evidence for that.

There's not? I would have said the miserable performance of Europeans whenever they ventured outside of air-conditioning certainly seemed like evidence.

('That's just them overheating in tropical conditions', someone immediately counters. Yes. Yes, it is.)

Also, this doesn't explain why Inuit aren't one of the highest-scoring groups by IQ.

Inuit have the largest brain size of any human group.

I'm not sure why this doesn't imply higher IQ; maybe poor nutrition/education? In any case, they do have the highest IQ of any Native American group, and of any human group outside East Asians and Caucasians.

According to a sketchy racist site: "Lynn also notes some anomalies in the cold winter theory of intelligence. The most striking: the Inuit, exposed to the coldest winter temperatures, have a brain size equal to East Asians, and yet have an average IQ of only 91. To explain this anomaly, Lynn proposes that additional genetic processes are important—such as population size. The larger the network of co-operating and competing population groups ("demes"), the faster any mutations for advantageous alleles can spread. So large landmass groups like East Asians and Europeans average higher IQs than isolated hunter-gatherer groups like the Inuit. "

More mutations at higher temperatures because there's more chemical activity in general? Does it make sense that breakage would tend to get ahead of repair/redundancy?

High temperature locations have more diseases, which could redirect resources from the brain to the immune system.

There are now a couple of papers out (in Science) in which people claim to have found a higher incidence of rare mutations that look deleterious in Africans (about 25% higher) : loss-of-function mutations, nonsynonymous changes that seem likely to have a functional impact, etc. I ran into some stuff in 2011 that suggested higher mammalian mutation rates in the tropics. I thought that if true, that would likely be the case in humans as well, which idea was fraught with implications. It might explain some observed patterns, such as the IQ-latitude correlation, differences in lifespans, miscarriage rates, etc. On the other hand, Usain Bolt does exist. On the gripping hand, brain function is surely more complicated than skeletal muscles, maybe it is the function most susceptible to such genetic noise. More than half of all genes are expressed in the brain.

If this pans out, I think everyone will love me. Right?

You probably hear this a lot, but I loved your book!

I was linked to your blog post on this the other day and found them pretty convincing. I misspoke in the first paragraph of this entry: I totally accept the latitude-IQ correlation, I'm just abandoning the idea that it derives from a hare-brained theory of mine about brain waste heat.

Everyone already loves you, Professor Cochran!

The person who successfully explains the distribution of intelligence in different populations will probably be taken in chains to Stockholm and fined several hundred thousand dollars.