In terms of compelling evidence, let’s start with a study published recently in the prestigious journal Nature Genetics.1 Tinca Polderman and colleagues just completed the Herculean task of reviewing nearly all twin studies published by behavior geneticists over the past 50 years....So, good news for those of you who are parents: Junior is a rat because of your rotten genetics, not because of your moral failings.
Before progressing, I should note that behavioral geneticists make a finer grain distinction than most about the environment, subdividing it into shared and non-shared components.1,2,3,4 Not much is really complicated about this. The shared environment makes children raised together similar to each other.3 The term encompasses the typical parenting effects that we normally envision when we think about environmental variables. Non-shared influences capture the unique experiences of siblings raised in the same home; they make siblings different from one another. Another way of thinking about non-shared environments is that they represent the parts of your life story that are unique from the rest of your family. Importantly, this also includes all of the randomness and pure happenstance that life tends to hurl in our direction from time to time. Returning to the review of twin research, the shared environment just didn’t matter all that much (that’s on average, of course, for some traits it mattered more than others). The non-shared environment mattered consistently.
The pattern of findings mentioned above is nothing new.1,2,3,4,5 The importance of genetics and the non-shared environment (and the relatively minor importance of the shared environment) was already so entrenched in behavior genetics that years before the Polderman study was published it had been enshrined as a set of “laws.”2 The BG laws, though, are based largely (but certainly not completely) on twin studies, the meta-analysis by Polderman et al. was comprised of twin studies, and if you pay attention to this sort of thing you’ve probably heard some nasty things about twin studies lately.3 You’ve read that twin studies contain an insidious flaw that causes them to underestimate shared environmental effects (making it seem like parents matter less than they do). The assumptions of twin research, however, have been meticulously studied. The methods of twin researchers have been around for decades and have been challenged, critiqued, refined, adjusted, and (perhaps most importantly) cross validated with other techniques that rely on different assumptions entirely.3,4 They work, and they work with impressive precision.
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).3
Well, and his peer group: it turns out that the 'socialization' that really matters is the kind of kids he runs with. "As Harris notes, parents are not to blame for their children’s neuroses (beyond the genes they contribute to the manufacturing of that child), nor can they take much credit for their successful psychological adjustment."
Psychoanalysts hardest hit.