[T]he institution of property protection can be regarded as only a necessary but not also as a sufficient condition of economic growth, that is of rising per capita incomes. So some other empirical factor which does not figure in pure economic theory must explain the length of the Malthusian Age and how we got out of it. And this missing factor is the historical variable of human intelligence.
Man is physically weak and ill-equipped to deal with brute nature. It was advantageous for him to develop his intelligence -- that is, his knowledge of cause and effect relations -- and to be successful as hunter and gatherers and even more so as agriculturalists (and keep in mind until about 1800 90% of the population worked in agriculture). This required some intelligence.
Not every person was equally intelligent, however, and higher intelligence translated into greater economic success and greater economic success in turn translated into greater reproductive success; that is, led to producing a larger number of surviving descendants. For the existence of both of these relationships, that is intelligence leads to success and greater success leads to reproductive success,there exists a massive amount of empirical evidence.
Now further, this tendency of selecting for higher intelligence would be particularly pronounced under harsh external conditions. If the human environment is unchangingly constant and mild as in the seasonless tropics for instance, where one day is like another year in and year out, high or exceptional intelligence offers a lesser advantage than in an inhospitable environment with widely fluctuating seasonal variations. The more challenging the environment, the higher the premium placed on intelligence as a requirement of economic and consequently of reproductive success. Hence the growth of human intelligence would be most pronounced in harsher -- and that historically of course in more northern -- regions of human habitation.
That's Hans-Hermann Hoppe, speaking at the Austrian Scholars Conference 2010 (audio available here).
I confess myself quite interested to learn that the climes where the Industrial Revolution occurred are more "challenging" than the Atlantic Hurricane Belt, the Sahara or Lapland.
Hat tips -- Roderick Long mentioned this speech in an email, which got me interested. Jonathan Carp mentioned the Inuits in passing in an email on the same thread, which gave me the title.