The cold winter theory is extremely important to HBD.  In fact I don’t even understand how one can believe in racially genetic differences in IQ without also believing that cold winters select for higher intelligence because of the survival challenges of keeping warm, building shelter, and hunting large game.  By contrast, warm climates select for small heads (and by extension smaller brains and low IQs) because in the tropics, an oversized head will overheat like a light bulb.

Nonetheless, there remains much skepticism of the cold winter theory, both from HBDers and HBD deniers.  One such skeptic is commenter MeLo who writes:

 Heidelbergensis’ brain size would be all you actually need to survive pretty much anywhere. Around 1200-1300 CC. It’s the same size as modern African hunter-gatherers(bushmen 1270), which implies bushmen are more than equipped to deal with cold conditions.

There are a couple problems with this reasoning:

The below map shows in red, the region where Homo heidelbergensis lived:


Below is a map of the World by temperature in January (cold climates are in Purple, very cold, in darker purple, and freezing in the very dark purple).  Notice how little overlap there is between the Homo heidelbergensis range in the above map, and the purple ranges in the below map (let alone darker purple ranges).


Even Neanderthals, who were not only more evolved than heidelbergensis, but had bigger brains, and were physically adapted to the cold,  scarcely lived in the coldest regions. There geographic range is shown in red below.


It seems modern humans are the only species in the Homo genus that is adaptable enough to survive extreme cold climates.  I suspect that during prehistoric times, a tribe needed an average IQ of at least 90 to live with such weather.  If the tribe’s  IQ fell below 90, there wouldn’t be enough people who could quickly make fire, build warm, sturdy water tight shelter, sew weather tight clothes, and hunt scarce large game.

One definition of intelligence is the (cognitive) ability to use tools, and scholar Richard Lynn cites research by Torrence (1983), showing:

an association between latitude and the number and complexity of  tools used by contemporary hunter-gatherers. He found that hunter-gatherer peoples in tropi-
cal and subtropical latitudes such as the Amazon basin and New Guinea typically have be-
tween 10 and 20 different tools, whereas those in the colder northern latitudes of Siberia,
Alaska, and Greenland have between 25 and 60 different tools. In addition, peoples in cold
northern environments make more complex tools, involving the assembly of components,
such as hafting a sharp piece of stone or bone onto the end of a spear and fixing a stone axe  head onto a timber shaft.