The above are some commonly accepted values for the heritabilities of complex traits in the scientific literature. By heritability I mean to refer to the proportion of the variation in the trait within the population which can be explained by variation of genes within the population. The reason I am very precise is that heritability should not be taken to be some sort of obvious correlation statistic. Even though height is highly heritable in modern societies, the average sibling difference is 1.8 inches (4.6 cm). But, heritability is informative when it comes to populations and patterns of variation that we see around us. A highly heritable trait is amenable to selection for a breeder, while a non-heritable trait is not. But just because a trait is highly heritable does not mean that environment does not matter. One can imagine a scenario of “all boats rising” where environment shifts the trait value equally across the population, while all the variation within the population is still due to genes.
I’m bringing all this up because W. Bradford Wilcox has a new piece in Slate, What’s the most important factor blocking social mobility? Single parents, suggests a new study. The variable what Wilcox is alluding to in the title is illustrated in the figure to the left: the proportion of single parents in the community is very predictive. Importantly he’s arguing for very powerful community level effects. And certainly the correlation is pretty impressive. And knowing the Left’s love affair with the idea of science, he flogs this correlation rather for all that it’s worth:
Throughout his presidency, Barack Obama has stressed his commitment to data-driven decision-making, not ideology. Similarly, progressives like Krugman have stressed their scientific bona fides, as against the “anti-science” right. If progressives like the president and the Nobel laureate are serious about reviving the fortunes of the American Dream in the 21st century in light of the data, this new study suggests they will need to take pages from both left and right playbooks on matters ranging from zoning to education reform. More fundamentally, these new data indicate that any effort to revive opportunity in America must run through two arenas where government has only limited power—civil society and the American family.
The author is a visiting scholar at the Right-leaning American Enterprise Institute, but he does a good job of being evenhanded and not overtly ideological from what I have read. W. Bradford Wilcox seems to be sincerely driven by a commitment to the social issues he writes about so often. He’s also intellectually honest enough to admit that the lead author of the study which reports this stark correlation “has been careful to stress that this research cannot prove causation.”
At this point you know where I’m going with this. Wilcox admits the complexity and confounds at the heart of phenomenon he’s trying to describe. Naturally one aspect he leaves out are the innate dispositions of individuals due to their heritable makeup. More concretely, personalities differ, and those differences have consequences, and those differences partly have a genetic component. I haven’t thought about all the policy implications of this, but I do know that it makes the story that Wilcox and company tell more complicated, and likely alters the nature of the solutions that they might posit (and definitely the effect sizes they might see). Conservatives often accuse Left-liberals of being “social engineers” who neglect the complex interdependencies of organically evolved cultures. The argument is that they presume that they can model cultural outcomes as if they were as predictable as thermodynamics. But modern American conservatives have fallen into a similar trap, with the mantra “the family” “the family” “the family” as a catchall solution to all social ills. As if society is a simple pliable physical process, and the family one of its easy-to-modulate regulatory components.
It is somewhat tedious to get on this high horse over and over, but it needs to be done. Modern Left-liberals certainly won’t do it. While conservatives harp on the family, liberals focus on the economy. Ultimately both parties are missing a part of the picture, but neither is going to challenge the other on their shared lacunae.