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Not so fast. If a climate promotes a gene for strong selection which results in a new behavioral trait, that is not the same as the climate causing an environmental change in behavior.

There are several factors affecting evolution of skin color in regional populations. UV radiation’s ability to effect folate and vitamin D levels seems to be most important historically. UV radiation is highly correlated to latitude. Diet seems to play a factor in this selection process as well (vitamin D and folate sources).

I suspect that behavioral traits associated with lighter pigmentation also play a role in the rapid spread of lighter gene variants in the last 10k years. Theres evidence that dark pigmentation in many species is associated with high libido, high aggression, etc. I have no idea if laziness is caused by pigmentation or another gene or by just simply being hot. I think there’s a constellation of behaviors that seem to “work” in primitive tropical populations like high libido, violence, high sociability and laziness (similar behavior patterns exist in pacific negritos and central africans) but we don’t know how much of these behaviors are implemented through the melanocortin system. Shitskins have higher sex hormone levels and higher frequencies of the “warrior gene” allele (MAOI-A variant). Clearly its not all about melanin.

A key part of our divergence from “tropical” people is the difference in economies even in the paleolithic. North eurasians had to rely on hunting more than gathering (plant food) since theres little plant food in winter. The tropics favored a matrilineal society since the women were the bread winners. Men led families as maternal uncles, not fathers. Polygamy meant paternity was uncertain.

Cold climate hunter gatherers relied on meat which favored a patrilineal system. Men who risked their lives bringing home the bacon needed to be assured of paternity, so no polygamy or at least no female promiscuity. This is presumably because men had more economic leverage than in the tropics. Patrilineality and monogamy appears to be necessary and sufficient for men to be bread winners and have lower male-on-male aggression for reasons I have stated ad nauseum elsewhere.

Tropical men had lesser incentive to be industrious to support families that they were less related to (e.g. maternal uncle’s half sister’s children) This is why modern day matrilineal hunter gathers (or groups who were so until recently) are the most backward economically. Men evolve to be competitive bread winners only under certain conditions. Else where the competition is about “muh dick”. I’m getting at an r/K selection dichotomy. So the question is not why tropical hunter gatherers are lazy but why would’nt they be.

But the paradox for me is this: if much of these behavioral changes are implemented through melanocortin system, then you have a sort of chicken or egg problem. Did lighter pigmentation caused by migration to higher latitudes make higher levels of civilization possible ? A massive selective sweep for light skin in Europeans and north east eurasians is attributed to agriculture (low vit D grain based diets) but that shift was contemporaneous with a massive increase in population density and maybe even rudimentary forms of law enforcement.

Well Ive gone on a tangent. Yes I agree there is a behavioral cline which is discernable in almost every sizeable country. I had a Korean friend who once described all the stereotypes which southern Koreans had of northern Koreans and vice versa. It was all really predictable stuff. This is clearly a case of convergent evolution, as its unlikely that northern koreans and chinese were unknowingly infiltrated by scandinavians with genes for more prudent habits. Its truly amazing to me that east asians are more related to abos than to whites and that their light skin is dependent on a different set of genes than our light skin. Convergent evolution explains our similarity to east asians and africans’ similarities to abos. Both cases are of two highly divergent groups.