Greg Cochran and Henry Harpending have recently proposed a hypothesis on their blog that posits that the lower average IQ of tropical peoples may be related to the number of fitness reducing mutations these people carry. Apparently, the rate of mutation is higher in the tropics. The majority of mutations that occur are neutral and harmless, but the majority of the remainder are harmful. Some of these are severely so, and they are rather quickly eliminated by natural selection. But most are only mildly deleterious, only slightly reducing fitness. It takes selection a long time to remove such mildly deleterious mutations; hence populations that experience a high mutation rate will accumulate a large amount of these fitness reducing genetic changes (i.e., genetic load) because they appear faster than selection can eliminate them. This has all kinds of ill effects for humans, as all these minor dings and dents can negatively impact the individual that possesses them, including lowering IQ among a host of other things.
This hypothesis is potentially huge, because it presents the first real challenge to the standard sociobiological paradigm, which asserts that higher average IQ evolved among Eurasians because of the greater demands encountered in winter climates. While I’ve asserted my own refinements to this paradigm, I haven’t challenged the basic structure, because there is indeed a very strong correlation between average IQ and latitude. Cochran’s & Harpending’s hypothesis, however, suggests an alternative pathway to the evolution of IQ.
This theory, incidentally, would explain the apparent IQ ceilings that seem to exist across the world. This particularly addresses the latitudinal correlation with brain size, as Cochran explains:
In fact, if this pattern is real and has existed for a long time, it will change selective pressures. In a high-mutation environment, brain function probably doesn’t deliver as much fitness per cubic centimeter – but those brains cost just as much per cubic centimeter. In that situation, selection would likely favor smaller brains (than it would in a lower-mutation environment). So we would expect to see smaller brains in populations with lower average IQ – not enough to explain all of the lower IQ, but some smaller – and we do.
My own thought—and Cochran’s—is that genetic load is only part of the explanation. Selection—such as according to standard HBD theory—still likely plays a large role, if not the dominant role. But genetic load could still be an important part of the puzzle.
But is it? How much evidence is there for the negative impact of genetic load on IQ and for its role in differences between average IQ between groups? I think that I may have found some, and it has something to do with connection between IQ and physical attractiveness.
Evolutionary psychologist Satoshi Kanazawa discovered, using the Add Health data, that there is a link between IQ and physical attractiveness, such that people who are physically attractive have higher IQs, on average, than those who are less attractive. This pattern remains regardless of race. Good looks are associated with more than just health.
Of course, using the same data, as previously mentioned, Kanazawa also discovered that Black women are, on average, less attractive than women of other races, for which he was almost “Watsoned”. But in his discussion about this, he makes an important point that may shed light on the connection between attractiveness and IQ.
Why is there a connection between attractiveness and IQ? Or, as the question should be, why the connection between unattractiveness and lower IQ? In his attempt to explain the lower average attractiveness of Black women, Kanazawa touched on one reason I believe is behind this link.
That is genetic load. Presumably, just as a high degree of genetic load can lower an individual’s IQ, it likely can also degrade his or her physical attractiveness. Ugly people may be dull and ugly because they possess a high degree of genetic load. And because genetic load is still with us (presumably for most populations, at least), this explains, at least in part, why evolution hasn’t gotten rid of ugly people.
But, as Kanazawa noted, Black men weren’t rated as less attractive than men of other races, on average. Indeed, another study has found that Black men were rated as more attractive than men from other races (and also found that Black women were rated as less attractive than women of other races, confirming Kanazawa’s “controversial” finding). This is the case even though Africans, both male and female, have a higher genetic load than other races.
So how do we reconcile these finding? The answer comes back to natural selection. As Steve Sailer discussed, there are different aspects of facial attractiveness. I propose that there are at least two dimensions that are important. One is overall conformity to the group average (as seen here from these facial composites from The Postnational Monitor), which is a sign of physical health—which can apparently be quantified as the degree of absence of deleterious mutations. The closer one’s appearance to the group average, the lower one’s genetic load is likely to be.
The other dimension is degree of gender-specific traits one possesses, which for men means strong jaws and brows, and for women means more gracile jaws and brows, and larger lips and eyes. This, I believe, explains the racial gradient in attractiveness as seen in the aforementioned study. In that study, there was in fact a reliable progression of attractiveness that went from Black -> White -> East Asian for women and in the opposite direction for men. This finding was consistent for the average ratings from all three of those races. This is likely because, as compared to Europeans, Blacks tend to be more masculine overall, while East Asians tend to be more feminine. The greater masculinity of Black male faces may have rendered them more attractive despite their higher overall genetic load (with the exact opposite likely being true for East Asian males—whose faces probably weren’t ugly per se, just too feminine). Conversely, the greater degree of female-specific features (especially neotenous ones) likely render East Asian female faces more attractive. Black women are unfortunately left with the worst of both worlds—higher genetic loads hence more dings and dents detracting from the group ideal—and fewer female-specific features to counteract this.
This racial lean towards one gender-typed set of physical features may be a result of fairly recent selective forces in Africa and Eurasia. For Africans, specifically West Africans (who we’re discussing most of the time), the selective pressures of the tropical farming system, where women did most of the work and polygyny rates were very high (60% of all married women in some cases), men were under more selective pressure than were women. This would have selective for genes that led to more attractive male forms even if it came at the expense of attractiveness in women. In East Asia, and to a lesser extent Europe, the selection for docility by strong state governments would have favored genes for feminization. As well, the early and universal marriage common in East Asia would have also served to reduce the selection for masculinity. (This is also true, to a lesser extent, for Europe east of the Hajnal line; as one can see from the above facial averages, Slavs appear to possess more feminine features than Western Europeans—I’ll discuss this more in my post on ideology.)
But, as Slate notes, there have been many intelligent people who have been rather unattractive. Indeed, I’m not sure how the connection between attractiveness and IQ holds for those who have very high IQs. Anecdotally we can all think of some brilliant folks who aren’t at all lookers. Some of this is just a natural consequence of the normal variation in both IQ and attractiveness. However, what if there are other factors operating?
Most traits are the result of many genes with small effects. But there are a few genes with large effects that contribute to many traits. What of individuals whose high intelligence is the result of the contribution of a few genes with large effects? Two things are possible then: in a person with little genetic load, these genes can have a large negative effect on attractiveness while boosting IQ (an example of such genes may be those for male pattern baldness). Or, they may provide a large boost in IQ for those with a large genetic load, and who are hence rather homely.
One additional piece of evidence for the connection between genetic load and intelligence is the connection between height and IQ. In the cited article, Kanazawa and Reyniers presented several possibilities why these two would be connected, primarily assortative mating (assortative mating of both taller and smarter men with attractive women), but the other explanation (not necessarily mutually exclusive) is higher genetic load impacting both height and IQ, since, as Cochran notes, taller people tend to have lower genetic loads.
I think there is enough for a decent case for a connection between genetic load and attractiveness and IQ. Indeed, if one looks cross racially, races that have been in the tropics for many millennia (Australoids and sub-Saharan Africans) are also (in my opinion) some of the least attractive (women only in the case of sub-Saharan Africans). This could be a sign of the very high genetic load among these groups. I await further analysis with more groups from more places around the world to see if this indeed a real phenomenon.