I review Michael H. Hart's answer to Jared Diamond at VDARE.com: Hart's Understanding Human History is a better History of Everything than Guns, Germs, and Steel. Here's an excerpt:
"Throughout history, most of the instances of people from one region attacking and conquering substantial portions of another region have involved 'northerners' invading more southerly lands."
(The biggest exception: the Arabs of the 7th Century A.D. And the Romans conquered in all directions.)
This overall pattern of north conquering south has long been apparent from the historical record—even though northern lands are generally less populous, due to shorter growing seasons.
For example, mighty China, a vast empire with a competent bureaucracy chosen by meritocratic tests, was never much threatened by southerners, but it built the vast Great Wall to keep out its much less numerous northern neighbors. Nonetheless,
Likewise, the vastly populous Indian subcontinent was seldom a threat to its northern neighbors, but was frequently overrun from the northwest.
This pattern has been validated by recent DNA studies. (Hart fails to mention this, which is surprising considering how otherwise up to date he is on the human sciences). In populations of mixed background, the male line of descent (as seen in the Y-chromosome) tends to derive from north of the homeland of the female line of descent (as seen in the mitochondrial DNA). Implication: men from the north more frequently overcame the men from the south and took their women.
Examples: Latin Americans (white fathers and Indian or black mothers), African-Americans (whites and blacks), Asian Indians (Aryans and Dravidians), and Icelanders (Vikings and Celts). Similarly, the Han Chinese, the world's largest ethnic group, are more likely to be descended from northern Chinese men and southern Chinese women than vice-versa.
Likewise, the man who left the largest footprint yet found on the Y-chromosomes of humanity was Genghis Khan from cold
The Manchu founder of the Qing dynasty that ruled
The pattern is even true in
Hart offers a simple, deliberately reductionist model for explaining this (and much else): Foresight is needed to survive cold winters. So harsher, more northerly climates select for higher average intelligence. And intelligence is useful in war.
Indeed, there is a positive correlation between latitude and the average intelligence of modern countries, as summarized in Richard Lynn's and Tatu Vanhanen's IQ and the Wealth of Nations. (Here's my table listing their data.) In 2006,
On the other hand, within continents there often aren't obvious latitude-related IQ disparities. For instance, the IQ differences among most European countries are too small to worry about.
Northerners have tended to be better at organizing on a large scale. This could be related to intelligence, but doesn't have to be. During WWII, for example, according to military historian John Keegan, the Italians were probably the worst soldiers in Europe and the Finns the best. But
No doubt other factors contribute to the long history of Northern military successes. For example, the ease of raising horses on the Eurasian steppe, varying family structures—and of course the ancient moral explanation, going back to the Roman historian Tacitus, that contrasts northern hardiness, self-sacrifice, and motivation with southern decadence, backstabbing, and enervation.
Nor is climate the only factor determining intelligence—or the Eskimos would be the smartest people on Earth. (They are, however, probably the smartest hunter-gatherers). [More]
A few years ago, an anthropologist emailed me to call my attention to a 1982 article on this tendency of the north to intrude more upon the south than vice-versa:
See "Winter temperature as a constraint to the migration of preindustrial peoples." John M. Whiting, John A. Sodergren, Stephen M. Stigler, American Anthropologist, June 1982
Main conclusions: 1. Based on the distribution of language phyla, the 10 degree centigrade (50 degree Fahrenheit) isotherm has been a major barrier to migration. (The isotherm is two lines going around the globe, one north and one south of the equator, at which the mean temperature in the coldest month is 10 degrees C.) Plenty of language families stretch a long ways longitudinally on either side of the isotherm. Not many cross it. (Indo-European, with its extension into
2.When language phyla *do* straddle the barrier, it's much commoner for cold-centered phyla to have warm-ward extensions than the reverse, indicating that migrations from high to low latitudes are more common than the reverse. The authors propose a technological explanation, drawing on earlier research on climate, clothing, and infant care: "It is easier for people who wear two layers of clothing to take one off when they move into a warmer climate than it is for single-layer people to produce a second layer when they move to a colder climate. Similarly it is much easier for cold-adapted people to substitute a shawl for a cradle as a device for carrying infants than it is for warm-adapted people to learn to make a cradle." Obviously this doesn't apply when people get clothing and cradles in stores instead of making their own.
In other words, cold weather favors a higher level of technological sophistication. (There were exceptions, such as the remarkably backward Tasmanians.)