As most of you know, Richard Lynn pushed the theory that the further North modern humans migrated during the ice age, the more IQ they needed to survive the cold winters, and so Northern populations evolved to be especially smart.  However lately people have been telling me that Northern populations have higher IQs, not because they’re genetically smarter, but because cold climates have less infectious disease which damage the brain during childhood.

Because this is a plausible alternative theory, I decided to check it out.

It turns out these people are citing a 2010 paper called Parasite prevalence and the worldwide distribution of cognitive ability by Christopher Eppig, Corey L. Fincher, Randy Thornhill.  The paper does indeed find that parasite load is a stronger predictor (-0.82) of a nation’s IQ than winter temperature is (-0.72). 

The authors concluded that when all other variables are held constant “infectious disease is the best predictor of intelligence by a large margin. The effects of years of education are not significant, while temperature and evolutionary novelty seem to have distinct predictive power beyond infectious disease.”

So while IQ differences between countries are related much more to a country’s health than to its genes, the genetic legacy of the ice age still has some predictive power.  Contrary to what many are saying, this study does not debunk Lynn’s cold winter theory, it merely states that Worldwide, one’s biological environment has much more effect on IQ than one’s DNA.

Of course Lynn already knew environment mattered greatly when discussing international IQ differences, which is why he stated that only half of the IQ deficit of Third World countries is genetic, though perhaps it’s less than half.

The study may have found even stronger support for Lynn’s cold winter theory if instead of using winter temperature as the measure of ancestral climate, they used skin color.  Average skin darkness correlates -0.92( Templer & Arikawa (2006) ) with national IQ, which trumps virtually all other correlations with national IQ, even parasite load.  Of course I’m well aware that Lynn’s IQ data has been severely criticized for inaccuracies and bias, but so far it’s the only worldwide database of directly measured IQ I know of.

 

 

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