Children making pillow lace for a home workshop. Germany, 1847. During the early stages of Europe’s market economy, successful entrepreneurs would expand their workforce by having more children.

There are several obstacles to our understanding of geographic variation in human mental performance.

First, the subject is taboo. When people do discuss it, they often resort to euphemisms, “code words,” and the like. The result, all too often, is confused thinking. When ideas cannot be expressed clearly, the resulting theory is likewise obscure.

Second, there has been a tendency to imitate the physical sciences by seeking a “unified theory,” i.e., Phil Rushton and r-K life history theory (Rushton, 2000), Ed Miller and parental investment (Miller, 1994), etc.

There is indeed a unified theory. It’s called evolution by natural selection. But natural selection acts in many different ways in many different environments. This could hardly be less true for our species, which has had to adapt to a wide range of physical environments—from the tropics to the arctic—and a wide range of cultural environments—from nomadic hunter-gatherers to socially complex urban civilizations.

Third, until recently, human evolution was supposed to have happened a long time ago, surely no later than the Pleistocene. Our mental traits, like all other traits, are thus a product of ancient environments, when humans lived by hunting and gathering. As for all of the later developments—agriculture, civilization, literacy, State societies, class stratification—these things have shaped us culturally but not genetically.

Well, they have shaped us genetically. Changes to the human genome have accelerated over the past 40,000 years and especially over the past 10,000 years (Hawks et al., 2007). We are a young species. Human nature—or rather natures—is largely post-Pleistocene.

Recent selection

Thus, one theoretical model cannot account for all or even most variation in cognitive capacity among present-day humans. The higher IQ of East Asians, for example, almost certainly came about during historic times and was probably favored by the widespread use of exams as a means of social advancement. Likewise, the higher IQ of Ashkenazi Jews and other European populations is probably post-medieval in origin and driven by the high fertility of successful entrepreneurs, particularly those in cottage industries who could expand their workforces only by having larger families (Frost, 2007).

Another relevant factor is the rise of the State, particularly its monopoly on violence (Frost, 2010). This is discussed with respect to English society in Gregory Clark’s Farewell to Alms. Clark (2007) argues that the slow but steady demographic expansion of the English middle class from the 12th century onward gradually raised the population mean for predispositions to non-violence, deferment of pleasure, and other future-oriented behavior. Although the embryonic middle class was initially a small minority in medieval England, its descendants grew in number and gradually replaced the lower class through downward mobility. By the 1800s, its lineages accounted for most of the English population.

This natural selection came to an end with the Industrial Revolution. Previously, successful entrepreneurs expanded their workforce primarily by having larger families. With the decline of cottage industry and the commodification of labor, it became possible to hire workers on a large scale. Henry Ford was a successful businessman, but his economic success did not translate into reproductive success. He had only one child.

No-so-recent selection

Even further back in time, neither Rushton’s model nor Miller’s fits all of the facts. Yes, cognitive capacity does seem to show some kind of relationship with family structure, specifically low incidence of polygyny and high paternal investment. I am not convinced, however, that this relationship is best understood in terms of K-type versus r-type reproductive strategy.

Today, most of the human gene pool is derived from populations that only 15,000 years ago were confined to the northern tier of Eurasia. These populations have since expanded southward into temperate and even tropical Eurasia, as well as Oceania and the Americas. In the process, they have displaced other populations that were nonetheless better adapted in terms of climate and ecology.

What was their competitive advantage? It could not have been a K-type reproductive strategy. If we look at present-day hunter-gatherers from the northern arctic and sub-arctic, we find that they pursue a moderately r-type strategy despite high levels of paternal investment. Traditional Inuit, for instance, have short inter-birth intervals, with menstruation being a rare occurrence.

The competitive advantage seems to involve three characteristics of ancestral northern Eurasians:

1. A predictable yearly cycle, which favored the ability to plan ahead and make future decisions in the present. Indeed, early modern humans had more complex tools and weapons at arctic latitudes than at tropical latitudes, apparently because of the yearly cycle of resource availability: “Technological complexity in colder environments seems to reflect the need for greater foraging efficiency in settings where many resources are available only for limited periods of time.” (Hoffecker, 2002, p. 135)

2. A low incidence of polygyny, which reduced male-male competition for mates and the consequent disruptive effects on social organization.

3. A high level of paternal investment in the family, which in turn emancipated women from food provisioning and enabled them to develop a ‘family workshop’ of garment making, structure building, food processing, etc. (Kelly 1995, p. 262-270).

These northern Eurasians were thus mentally pre-adapted, despite their simple social organization, for later technological developments, even though such developments were possible only in more southern environments for which these populations were less ecologically adapted. It is perhaps no surprise that they were able to expand southward into the temperate and tropical zones, eventually peopling almost all of Eurasia, Oceania, and the Americas.