However, while the data presented is fascinating I find the conclusions he draws highly questionable.
For example he writes that:
Then goes on to say 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.
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.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.
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.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).
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)
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.