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Waste Heat II: Some Like It Hot [Aug. 8th, 2012|10:05 pm]
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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.

xuenay links to Gregory Cochran's writings on difference in mutational load in the tropics and the temperate regions. Apparently mutations happen more quickly in higher temperatures (why?) and since most mutations are harmful and the brain is the most easily-harmed organ in the body, we would expect higher-temperature regions to produce less efficient brains. If brains are less efficient, it's less valuable to have them and we could expect them to be smaller; this provides an alternative (and better) explanation for variation in cranial capacity (and IQ) with latitude.

alicorn24 points out that mammalian diving reflex explains why cold water on the face is invigorating better than a selective brain cooling explanation. We were discussing last night whether cold water on any other part of the body, or cold air on the face, or any other combination other than water + face, was also invigorating and settled on "Um, maybe?". Also, does cold water to the face really only work at < 70 degrees F? And does rubbing a little bit on from the sink really trigger the diving reflex?

I am willing to retract my claim that waste-heat dissipation explains the latitude-IQ gradient in favor of Cochran's much superior theory, and say diving reflex probably explains away cold water to the face, but I'm not quite abandoning the rest of the theory - yawning, boredom and tiredness - just yet.
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[User Picture]From: gcochran
2012-08-09 07:39 am (UTC)

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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?
[User Picture]From: squid314
2012-08-10 02:27 am (UTC)

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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!
[User Picture]From: gcochran
2012-08-10 03:03 am (UTC)

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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.