Evolutionary psychologists attribute the superior IQs of light-skinned populations to genetic imprints left by millenary processes promoted by cold. But a novel theory that explains IQ gains observed across recent generations ascribes them to a latitude→UVB radiation→vitamin D3→parents' sexual hormones→family size→child's intellectual environment→IQ chain of effects. Analyses of 506,347 Peruvian children's math and reading scores from a national census confirmed that complex cognitive ability increases with absolute latitude even under tropical megathermal climates and decreases with high altitude above sea level, birth rate and social development mediate most of the effects, and reading is more strongly influenced than math. The findings weaken the evolutionary cold hypothesis and strengthen the view that contraception has the potential to reduce latitudinal IQ gaps. © 2014 Elsevier Inc.