Razib Khan on Human Differences

Drawing on the work of James F. Crow, Razib Khan offers a stimulating discussion of human differences. 

As Crow noted above if you sample from the tails of the distribution then very modest differences between groups become rather salient. Consider long distance running. To be successful in international competitions one presumably has to be many, many, standard deviations above the norm. One can’t be a 1 out of 100, or 1 out of 1,000. Rather, presumably one should be 1 out of hundreds of thousands, at a minimum. This would be the fastest ~100,000 or so people in the world (out of 7 billion). With this in mind, we should not be surprised a priori at the success of the Kalenjin people of Kenya in this domain. They may have both the biological and social preconditions which allow their distribution of talent to be moderately above that of the human norm. Even a marginal shift can make a huge difference at the tails. 1 out of 100,000 is 4.26 deviation units above the mean. Increasing the mean of a population by half a standard deviation units (e.g., if 100 is the mean, 15 is the standard deviation, then for the population with the higher mean you’d be at 107.5) results in a disproportion in ratio of above 8:1 at 4.26 units (as measured in the first population). This is modest, about 1 order of magnitude, but consider possible gene-environment correlations and synergies that might ensue when you have a critical mass of very fast individuals. This could amplify the effect of a difference in distributions on a single variate (more importantly I suspect, consider that virtuosity in many domains requires an intersection of aptitudes many units deviated from the norm across many traits).

In the early 2000s James F. Crow was responding to the Human Genome Project. As has been thoroughly covered elsewhere human genomics has probably underwhelmed in terms of outcomes 10 years out. But it is often the case that with new technologies we overestimate the short-term change which they will effect and underestimate their long-term consequences. I believe with the rise of mass genomics, a radical increase in population coverage and full genome sequencing, we may finally start to adduce the underpinnings of quantitative traits. We already have indirect methods, but I believe that by 2020 we will have direct means at our disposal. We’ll have a good sense how deeply humans are commensurable on a population genetic level. I doubt it will change much in our values, but it may entail some rhetorical adjustments.

This kind of discussion tends to people uncomfortable, for obvious reasons. As Razib observes earlier in the post, “whenever a society singles out individuals who are outstanding or unusual in any way, the statistical contrast between means and extremes comes to the fore. I think that recognizing this can eventually only help politicians and social policymakers.” So when we single out individuals with unusually high IQs, for example, the fact that a disproportionately large share are drawn from some groups and not others can be seen as problematic. There are two thoughts I’d like to add.

(1) IQ seems to vary over the life course, as Sue Shellenbarger reports:

There are practical steps people can take to see longer-term IQ changes. A 30-year study at the National Institute of Mental Health found that people whose work involves complex relationships, setting up elaborate systems or dealing with people or difficult problems, tend to perform better over time on cognitive tests. Test scores of people whose jobs are simple and require little thought actually tend to decline, according to the research, published in 1999 in Psychology and Aging.

People often lament the fact that our economy is changing in such a way that, as Arnold Kling has observed

A job seeker is looking for something for a well-defined job. But the trend seems to be that if a job can be defined, it can be automated or outsourced.

The marginal product of people who need well-defined jobs is declining. The marginal product of people who can thrive in less structured environments is increasing.

On one level, high IQ individuals thrive in jobs that aren’t well-defined. Yet jobs that aren’t well-defined might tend to increase the IQ of those who have them. So perhaps the much-lamented fact that well-defined jobs are evaporating is actually a good thing.

(2) There is good reason to believe that environmental influences count for a lot. Garett Jones cites interesting research in “National IQ and National Productivity” to this effect:

A study of excessive fluoride in Indian drinking water found a 13 IQ point-difference between children “residing in two [separate] village areas of India with similar educational and socioeconomic conditions” (Trivedi et al. 2007, 178). If even half of this relationship is genuinely causal, and if intelligence has some of the technological and political spillover effects discussed below, then public health matters are of first-order concern for economic development.

Arsenic and fluoride exposures are also associated with low IQ in the People’s Republic of China’s (PRC) Shanxi province, even when comparing “groups [who] lived in rural areas with similar geographic and cultural conditions and a comparable level of socioeconomic development” (Wang et al. 2007, p. 664). High arsenic exposure was associated with a 10-point IQ gap, and high fluoride exposure with a 4-point gap. In both cases, the “normal” group had an IQ of 105, 5 points above the US mean.

In the Visayas region of the Philippines, Solon et al. (2008) found evidence that lead levels reduced the IQ of children. In their study, one microgram of lead per liter of blood was associated with a 2.5 point reduction in the verbal IQ of older children, and a 3.3 point reduction in the IQ of young children. In their sample of children, the levels of lead in the blood averaged 7.1 micrograms per liter, so lead exposure could be costing the average child in this sample 15 IQ points even under conservative estimates.

In an experimental nutritional study in Pune City, India, 10 weeks of zinc supplementation caused a 15–25 percent increase in the number of correct answers on the Raven’s Progressive Matrices (Tupe and Chiplonkar 2009).

What we should care about is upward absolute mobility in IQ across the spectrum. Addressing environmental influences with greater care could be helpful in this regard.

Reihan Salam — Reihan Salam is executive editor of National Review and a National Review Institute policy fellow.

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