For years I’ve been defending Lynn’s rule (that cold winters selected for intelligence at least in humans) and people would find one or two exceptions (Ashkenazi Jews being smarter than Eskimos despite the latter evolving in a much colder climate) and declare the whole thing pseudoscience.

Yet these same people believe in Bergmann’s rule (cold winters selecting for bigger animals). And even when these people would admit that cold adapted people are smarter, they would give all the credit to Bergmann’s rule, insisting they’re only smarter because the cold selects for big brains, with intelligence just being a byproduct rather than having adaptive value in its own right.

However Davide Piffer found that not only are education genes (a proxy for genetic IQ) strongly correlated with latitude at the population level, but they’re more than twice as so correlated as height genes!!! Piffer writes:

This shows that the high IQs of cold adapted people can not be explained by bigger bodies keeping us warm, and since bigger bodies have bigger brains, IQ is just a bonus. If that were the case, body size would better correlate with latitude than cognition does since it would be the direct cause. Instead it’s just the opposite! Surviving the cold requires intelligence, and since intelligence requires brain size which requires body size, big bodies are just a bonus.

In fact when it’s comes to the cold, there’s no evidence that body size has any adaptive value in its own right, and that’s because unlike other animals, we have intelligence which is your ability to adapt. When you yourself can adapt, you don’t need your body to do likewise. We didn’t need to evolve morphologically to survive the cold because we evolved culturally, except for that aspect of morphology that allows culture: brain size.

Of course this only undermines Bergmann’s rule (in humans). It’s still possible that Allen’s rule, which predicts that surface area to volume declines as a function of latitude, has some relevance in humans but don’t hold your breath.