We hypothesized that correlations would be higher for mean winter temperatures (January in the Northern Hemisphere and July in the Southern Hemisphere) than for mean summer temperatures.

Appendix 1: Major theories supporting the evolution of population specific difference in cognition Selection due to differences in Population Density Cochran and Harpending, 2009.

The 10,000-year explosion: How civilization accelerated human evolution (Here’s a decent review: Gorelik and Shackelford, 2010.

Their temperature and IQ analyses have been descriptive rather than quantitative, however.

In the present quantitative study, we predicted a negative correlation between IQ and temperature.

It is viewed by the present authors as a multigenerational reflection of the climates one’s ancestors have lived in for thousands of years.

Another reason to predict correlations of IQ with temperature and skin color is the product–moment correlation reported by Beals, Smith, and Dodd (1984) of 0.62 between cranial capacity and distance from the equator. based on findings from every continent and representing 122 ethnically distinguishable populations.

If there were a sufficient number of novel, non recurrent problems throughout human evolutionary history, any genetic mutation that allows its carrier to think and reason logically would have been selected for.

Given the extraordinary constancy and continuity of the EEA, general intelligence in its evolutionary origin was not general at all, and its importance was limited to occasional problems that other evolved psychological mechanisms could not solve.

Chemostat experiments on Escherichia coli show a continued response to selection (6), with continuous and repeatable responses in large populations but variable and episodic responses in small populations (7).

These results are explained by a model in which smaller population size limits the rate of adaptive evolution (8). Population Differences In Intelligence: Causal Hypotheses. In: The g Factor: The Science of Mental Ability Jensen, 2006.

A review of Gregory Cochran and Henry Harpending, The 10,000 Year Explosion: How Civilization Accelerated Human Evolution.