It seems to be almost an article of faith among those who study and theorize about such things that those peoples who had to adapt to colder climates developed greater intelligence as a result.
If you look at the general distribution among the races, the highest average IQs did develop among races which evolved at a good distance from the equator, i.e., the northern Europeans and the northeast Asians. At a certain level, that makes sense: surviving a long, frigid winter required planning and foresight in a way that living in the tropics did not. People in colder climates had to figure out how to build fires, built shelters, dress themselves in animal skins, and wrest a living out of much harsher, bleaker landscapes.
But the pattern is far from perfect.
The southern Chinese -- the Han -- seem to be just as intelligent as northern Chinese, on average. And the Nepalese and Mongolians, both of whom lived in cold climates, aren't known for their high average IQs. Both are admirable, hardy peoples, but neither group, to my knowledge, ever invented anything which has benefitted mankind overall. The Mongolians, by dint of their ferocity and hardiness, at one point conquered most of the known world. But the Chinese, including those who lived near present day Shanghai, seem to have won out on the IQ sweepstakes.
Why aren't Native Americans -- who, after all, came across the Bering Strait -- known for their high IQs? By the cold climates result in higher IQs line of reasoning, Eskimos ought to be the smartest people of all; but that doesn't seem to be the case.
Nothing of significance was ever invented in Siberia, either, for that matter.
India, despite its reportedly low average IQ (as referenced five posts ago), developed a relatively advanced culture. Angkor Wat was built in the hot, steamy jungles of Cambodia. And the Mayans not only developed the only known written language in the pre-Columbian Americas, but built pyramids to boot -- all in hot, steamy Central America.
Speaking of pyramids, the most sophisticated ones were built in Egypt, as long ago as 2600BC. Egypt is located right below the Tropic of Cancer.
Two thousand years ago the original Greeks and Romans, who lived in a more temperate climate then the northern Europeans, had the most advanced civilizations in the world. They subsequently interbred with their slaves, and their average IQ went down. But before that, they both led -- and conquered -- the world.
It's true, you don't have to plan ahead quite as far where there is no winter. But there's no reason intelligence would help just as much in the tropics as elsewhere. Wouldn't the ability to track animals, to build solid two story houses, to invent the wheel, to make better weaponry (for both hunting and waging war), and to domesticate beasts of burden have all have helped in conquering (and outbreeding) one's neighbors in the tropics?
Hot climates -- both arid and humid -- come with their own set of challenges. Wouldn't inventing irrigation and agriculture have helped people in sub-Saharan Africa or (pre-colonial) Australia? And wouldn't those who knew how to use them gradually displace those who didn't?
The different races did end up with varying levels of intelligence. But it seems to be just genetic chance, the great roulette wheel of mutation, that dictated which peoples developed greater intelligence.
It's easy to see why pale skin and thinner nostrils evolved: they were direct adaptations to less sunlight and the cold.
But intelligence? It helps everywhere. I think it's just chance that some races evolved more than others.