Twin studies are the foundation of realism in all subjects pertaining to human beings (although their implications are wider). They reveal two crucial pieces of information:
(1) Heredity overwhelms environment in the (rigorous, statistical) explanation of human psychology, and
(2) Humans are massively predisposed to under-emphasize hereditary factors in the folk explanation of human psychology (including their own).
Both points emerge lucidly from Brian Boutwell’s article on twin research in Quillette:
Based on the results of classical twin studies, it just doesn’t appear that parenting — whether mom and dad are permissive or not, read to their kid or not, or whatever else — impacts development as much as we might like to think. Regarding the cross-validation that I mentioned, studies examining identical twins separated at birth and reared apart have repeatedly revealed (in shocking ways) the same thing: these individuals are remarkably similar when in fact they should be utterly different (they have completely different environments, but the same genes). Alternatively, non-biologically related adopted children (who have no genetic commonalities) raised together are utterly dissimilar to each other — despite in many cases having decades of exposure to the same parents and home environments.
Without wanting to play down the importance of the parenting angle, it’s worth bearing in mind that this is a rare zone where it remains politically acceptable to bring hereditarian findings to the table. Upsetting parents is still OK, and even vaguely commendable, so it provides a doorway through which to introduce matters of far broader significance. The truly critical point, from the perspective of this blog, is that we should expect a systematic cognitive bias against the influence of heredity and thus — intellectual integrity demands — we should lean against it.
There’s an important lesson here:
Children who are spanked (not abused, but spanked) often experience a host of other problems in life, including psychological maladjustment and behavioral problems. In a study led by my colleague J.C. Barnes, we probed this issue in more detail and found some evidence suggesting that spanking increased the occurrence of overt bad behavior in children. We could have stopped there. Yet, we went one step further and attempted to inspect the genetic influences that were rampant across the measures included in our study. What we found was that much of the association between the two variables (spanking and behavior) was attributable to genetic effects that they had in common. The correlation between spanking and behavior appeared to reflect the presence of shared genetic influences cutting across both traits.
Parents are twin sources of influence. They “pass along two things to their kids: genes and an environment” — which facilitates the misattribution of genetic to environmental factors. If you find yourself regularly spanking your kids, it’s very likely that you’ve genetically-endowed them with the same spank-worthy characteristics you have yourself (because you were spanked as a kid, too, right?). The environmentalist delusion practically leaps out of this situation, pre-packaged for credulous belief.
See original (of both quotes) for references.
(Don’t just read the whole of Boutwell’s article, read the whole of Quillette.)