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Thursday, March 06, 2014

Not (all) in our genes?


Economic historian Greg Clark describes his latest research (and new book) in the NYTimes:
Your Ancestors, Your Fate: ... my colleagues and I estimate that 50 to 60 percent of variation in overall status is determined by your lineage. The fortunes of high-status families inexorably fall, and those of low-status families rise, toward the average — what social scientists call “regression to the mean” — but the process can take 10 to 15 generations (300 to 450 years), much longer than most social scientists have estimated in the past.

We came to these conclusions after examining reams of data on surnames, a surprisingly strong indicator of social status, in eight countries — Chile, China, England, India, Japan, South Korea, Sweden and the United States — going back centuries. Across all of them, rare or distinctive surnames associated with elite families many generations ago are still disproportionately represented among today’s elites.

... Our findings suggest, however, that the compulsion to strive, the talent to prosper and the ability to overcome failure are strongly inherited. We can’t know for certain what the mechanism of that inheritance is, though we know that genetics plays a surprisingly strong role. Alternative explanations that are in vogue — cultural traits, family economic resources, social networks — don’t hold up to scrutiny.

... Our findings were replicated in Chile, India, Japan, South Korea and, surprisingly, China, which stands out as a demonstration of the resilience of status — even after a Communist revolution nearly unparalleled in its ferocity, class hatred and mass displacement.

... 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.

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. ...  [ Italics mine ]
These results, and the original working paper in which they first appeared, were discussed in an earlier post:
While at UC Davis to give a colloquium earlier this week, I had the pleasure of meeting economic historian Greg Clark in person. Here's a sample of his latest work, which suggests that convergence of social classes has been surprisingly slow: averaged parent-child correlations of variables such as wealth, education and occupation are in the 0.7 -- 0.8 range over the last 200 years, the same as found in India, with its caste system! IIRC, Greg said he got the idea of using rare surnames from Nicholas Wade during an interview :-)
Correlations as high as 0.7 -- 0.8 are implausible from genetic factors alone without highly assortative mating. Traits such as height and IQ have narrow sense heritabilities as large as h2 ~ 0.6, so fraction of variance accounted for is ~ 60%, and midparent-child correlation as high as ~ 0.8, but under even somewhat random mating the parental midpoint is significantly closer to average than the phenotype of the more exceptional parent. This would cause children to regress to the mean much faster in height and IQ than in social status as indicated in Clark's data. It's also important to note that social status itself is only imperfectly correlated to observable phenotypes such as IQ, Conscientiousness or Extraversion. See Intergenerational mobility: Bowles, Gintis, Clark for more.

It seems likely that there is a social component which boosts the correlation due to genetic factors. This is not implausible (i.e., kids get a leg up in social status due to parenting or purely financial factors), but somewhat vitiates Clark's conclusion in the NYTimes essay above.

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