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Cold Winter Theory (CWT) is the theory that population differences in IQ are largely explained by the ancestral climates that the peoples evolved in, with colder climates selecting for higher IQs because of the difficulty figuring out how to build warm shelters, make warm clothes, create fire, get food etc. Modern CWT can be credited to Richard Lynn, though the idea is so intuitive that it was independently inferred by multiple historical thinkers throughout the centuries.

Now if you don’t believe population IQ differences are genetic in origin, then you don’t need an evolutionary theory like CWT to explain the correlation between a population’s ancestral climate and their mean IQ; in theory it might be explained by non-genetic factors like parasite load.

But if you do believe they’re genetic, CWT is the obvious cause: Hominoids have spent 25 million years adapting to the tropics so these may not require as much novel problem solving as the arctic, which we only encountered in the last 40,000 years. Among extant hunter-gatherers, the higher the latitude, the more diverse and complex their tool kit. There’s a reason people travel South for vacation and take vacation in the summer and why many camp grounds close for the winter. It seems cold weather is generally more challenging than warm weather.

Nonetheless I’ve been alerted to yet another attempt to debunk CWT, this time by W. Buckner on a blog called TRADITIONS OF CONFLICT (hat-tip to MeLo & RR). Buckner makes three main arguments against CWT.

Argument 1: Climate can’t explain the low IQ of Bushmen because the Kalahari is sometimes cold.


While it’s true that temperatures can sink as low as 0 °C in the Kalahari desert, this is nothing compared to the lows of -30°C in Ukraine, -52°C in Kazakhstan, and -68°C reached in Russia; three countries that makeup the Pontic-Caspian steppe, the homeland of the Indo-Europeans, far and away the most successful language group on the planet, giving rise to nearly half of the World’s population. With their wits perhaps sharpened by millennia of surviving extreme cold, they domesticated the horse and used them to brilliantly exploit the wheel, allowing their chariots to conquer almost everyone from Europe to India in record time.

Argument 2: Cold climates don’t require more intelligence to hunt because tropical people hunt too.

CWT claims that because plant foods are scarce in cold, high latitude places, people needed to be smart enough to cooperatively and strategically hunt large game, while tropical peoples could mindlessly pick berries all day. Buckner debunks this claim by noting that hunter-gatherers of all latitudes depend roughly equally on hunted animals for subsistence.


While Buckner might be correct that today, even tropical hunter-gathers depend as much on hunted animals as their Northern counterparts (at least land-animals, Northern hunter-gatherers do more fishing); it was likely untrue in the Paleolithic when population differences were evolving.

Smithsonian Magazine writes:

Living in Eurasia 300,000 to 30,000 years ago…in places like the Polar Urals and southern Siberia—not bountiful in the best of times, and certainly not during ice ages. In the heart of a tundra winter, with no fruits and veggies to be found, animal meat—made of fat and protein—was likely the only energy source.

Further evidence that cold climate Paleolithic peoples were more hunting dependent than their tropical counterparts is the fact that the former likely drove the mammoth to extinction, while the tropical dwelling elephant remains extant.

Argument 3: cold climates don’t require more intelligence to make clothes because tropical tribes can make clothes too.

Part of CWT is that the need for warm clothing as humans migrated North selected for high intelligence because those lacking the cognitive ability to make such clothes quickly froze to death (or their babies did) leaving those with high IQ DNA as the survivors.

To counter this point, Buckner mentions the elaborate costumes donned by the Bororo hunter-gatherers of Mato Grasso, Brazil during ceremonies, to prove that tropical people evolved just as much tailoring talent.

Anthropologist Vincent Petrullo is quoted:

The dancer was painted red with urucum and down pasted on his breast. His face was also smeared with urucum. Around his arms were fastened armlets made from strips of burity palm leaf, and his face was covered with a mask made of woman’s hair. The foreskin of the penis was tied with a narrow strip of burity palm leaf, for these men under their tattered European clothing still carry this string. A skirt of palm leaf strips was worn, and a jaguar robe was thrown over his shoulders. The skins of practically every speeies of snake to be found in the pantanal hung from his head down his back over the jaguar robe, which was worn with the fur on the ontside. The inner surface of the hide was painted with geometrie patterns, in red and black, but no one could explain the symbolism. A magnificent headdress consisting of many pieces, and containing feathers of many birds of the pantanal completed the costume with the addition of deerhoof rattles worn on the right ankle.

Bororo ceremony from Lowie (1963)


There are three problems with Buckner’s thesis:

Firstly, although the Bororo currently live in the tropics, they are descended from cold adapted people who crossed the Beringia land bridge from Siberia to present-day Alaska during the Ice Age, and then spread southward throughout the Americas over the following generations. Their tailoring skills may have evolved during those ancestral cold journeys.

Secondly, just because some members of the Bororo have elaborate tailoring skills does not mean these people on average have the tailoring skills of high lattitidue hunter-gatherers. The existence of a few talented tropical tailors no more debunks the tailoring supremacy of high latitude people than the existence of a few really tall women debunks the male height advantage.

Lastly, although the Bororo costume is elaborate, it mostly just consists of wearing many skins on top of one another and attaching lots of things to one’s body. While this is impressive, it is nowhere near the proficiency of making body hugging clothes that cling to one snugly during the fierce winter. It reminds me a bit of cold nghts where I throw more and more blankets on myself to feel warm. This never works as well as putting on a pair of tightly knit jogging pants and a figure hugging sweater.

For all their pomp and circumstance, one dressed only in ceremonial Bororo costume could expect frostbite in less than 5 minutes during ice age winter Russia. Clearly this is nowhere near solving the problem of warm clothing, and that’s because it makes no use of one of the most revolutionary inventions of all time.

According to journalist Jacob Pagano  “…researchers found that humans developed eyed sewing needles in what is now Siberia and China as early as 45,000 years ago.” 

So crucial were eyed sewing needles that they are credited with allowing our species to out-survive the Neanderthals. A 2010 article in the guardian describes archaeologist Brian Fagan’s view:

While Neanderthals shivered in rags in winter, humans used vegetable fibres and needles – created by using stone awls – to make close-fitting, layered clothing and parkas: the survival of the snuggest, in short..

Of course no one is suggesting that cold climate was the only cause of population IQ gaps (it certainly doesn’t explain the high IQs of Ashkenazi Jews who largely descend from the warm Middle East). But it may help explain the more ancient differences between macro-level populations like North East Asians, West Eurasians and those from the tropics. I find it interesting to note that IQ tests involving spatial ability show larger gaps between humans from warm and cold regions than tests involving verbal skill. This is the opposite of what a culture bias explanation would predict, but is consistent with CWT since natural selection may have favored spatial ability in the cold for sewing, building shelters, making fires and hunting etc.