Sunday, February 23, 2014

Heritability of Personal Characteristics Does Not Imply Heritability of Social Characteristics

Gregory Clark has a very interesting article in the NY Times regarding research he has conducted tracking surnames and high status occupations. I recommend reading it.

However, while the data presented is fascinating I find the conclusions he draws highly questionable.

For example he writes that:

The notion of genetic transmission of “social competence” — some mysterious mix of drive and ability — may unsettle us. But studies of adoption, in some ways the most dramatic of social interventions, support this view. A number of studies of adopted children in the United States and Nordic countries show convincingly that their life chances are more strongly predicted from their biological parents than their adoptive families. In America, for example, the I.Q. of adopted children correlates with their adoptive parents’ when they are young, but the correlation is close to zero by adulthood. There is a low correlation between the incomes and educational attainment of adopted children and those of their adoptive parents.
Then goes on to say that:

These studies, along with studies of correlations across various types of siblings (identical twins, fraternal twins, half siblings) suggest that genetics is the main carrier of social status.
If we are right that nature predominates over nurture, and explains the low rate of social mobility, is that inherently a tragedy? It depends on your point of view.
I have to confess that I'm not as familiar with studies showing correlations between children's incomes and their adoptive parents, what little I have read does seem to indicate the correlation is much stronger than it is with IQ making this assertion questionable.

The real problem, however, has to do with the vastly different timing of reversion to the mean in IQ and social status. Dr. Clark is writing about reversion to the mean taking 15 or more generations. However, reversion to the mean with IQ only takes a couple of generations. I found this blog post by  Steve Sailer illustrating this, I'm not really familiar with the blog so can't vouch for the source but it is consistent with what I know from more formal reading:

The speed of the regression to the mean.
If one starts with two parents whose IQs are 160 and looks at the average IQs across generations the speed of the regression to the mean is quite fast.

Parents 160, 160
Children average 136 (assume these mate with a 136)
Grandchildren average 122 (assume these mate with a 122)
Greatgrandchildren average 113 (assume these mate with a 113)
How can genetic reversion to the mean explain the very slow social reversion to the mean? There is almost an order of magnitude difference in speed (2 generations vs 10 - 15).

Furthermore, while IQ studies tend to show high correlations between IQ and job performance the correlation between IQ and social status or income is much lower. The data certainly hint that social outcomes are the result of something other than merit and it stands to reason that something other than genetic heritability of merit is at work. Of course, there could be a strong genetic component that is not linked with ability, it is pretty well established that people tend to like and hire people more like themselves so it may be that non-performance related characteristics are being selected for and leading to unequal social outcomes. But the implications of this are very different than if elite selection is based on performance related personal characteristics.

To mention another major issue, personal characteristics associated with success have changed radically over the past 300 - 450 years. In the 18th century membership in the elite meant living a life of leisure. Only little people worked and commercial striving was considered crass. Attitudes like this persisted into the next century. How is it that a society which selected for vastly different personal characteristics would result in a better genetic profile for their heirs in the modern world?

The question remains valid over shorter time frames. The kinds of work that are most remunerative have changed a great deal over only the past century. We associate very different characteristics with success than our great grandparents. How can selection pressures for a different set of traits result in the traits being selected for today being more prevalent in high status families?

While Clark's research is fascinating I just don't find the conclusions he tries to draw from it convincing. There are much easier links to be drawn from social power to outcomes than from social power to genetics to outcomes. Over the long time period written about reversion to the mean in status can be adequately explained by the existence of individuals with below average competence.* There is no strong grounds to assert that this heritability of status has anything to do with the heritability of ability; these are concepts that can remain distinct and the evidence I'm aware of, at least, is more consistent with separate heritability than joint heritability.

*Explanations involving social power are attempting to explain why individuals of moderate ability manage to gain and maintain power while individuals of high, but not exceptional, ability do not. They do not claim that individuals of low or no ability can gain positions of high power and influence. While this can happen under some regimes, like primogeniture in the middle ages in some countries, the normal state for societies is to have mechanisms to week out individuals with exceptionally little ability while maintaining the position of individuals with average or better endowments.

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