In the nature vs. nurture debate it is common to look at the fraction of the variation in outcomes due to genetic factors “nature”), and the fraction of variation in outcomes due to other factors (“nurture” + other things). Noah Smith and I discuss these kinds of comparisons in “There’s One Key Difference Between Kids Who Excel at Math and Those Who Don’t” and I look at them even more closely in “How to Turn Every Child into a ‘Math Person.’” The thing people often don’t realize is that how much of the variation in outcomes is due to genes and how much is due to upbringing are as much a reflection of how much genes and upbringing vary in the population of interest as it is about the strength of the effects of genes and upbringing.

For example, the fraction of the variation accounted for by genes is much, much larger if one is looking at many species than if one is only looking only at members of one species: homo sapiens. The reason racist views about the genes of different ethnic groups are wrong is that Homo sapiens descended from a small group of common ancestors not that long ago at a time when only a few humans were left, and there has been a lot of mixing of the gene pool in the thousands of years since. The otherwise tragic extinction of Homo floresiensis 12,000 or so years ago saves us from serious racism against a relative much closer than chimpanzees, but distant enough that claims of substantial genetic differences would actually be true. 

Focusing in on nurture, the fraction of the variation accounted for by upbringing is less if one is looking at the population of adopted kids (say identical twins adopted into different families), simply because adoption agencies try and to some extent succeed at screening out the lower tail of people who would be bad parents (along with screening out many people who would be great parents). At the other extreme, the striking differences in human behavior across cultures have to be attributed mostly to differences in upbringing.

Differences in human behavior are so large between different cultures because the influences of everyone else in the society–and the structure of the society itself–are added to the influences of parents. Psychologists often emphasize how much people’s behavior is affected by the situations they are in. But the situations they are in have a lot to do with the culture they are in. 

I emphasized in my column “Why You Should Care about Other People’s Children as Much as Your Own” that how we set up our culture has a big effect on how children turn out. It is our responsibility as adults to make sure that the next generation is better than we are. This view is one I share with John Stuart Mill. He emphasizes the importance of how a society raises its children and how effective its power can be in that child-rearing in On Liberty, Chapter IV, “Of the Limits to the Authority of Society over the Individual” paragraph 11:

But with regard to the merely contingent, or, as it may be called, constructive injury which a person causes to society, by conduct which neither violates any specific duty to the public, nor occasions perceptible hurt to any assignable individual except himself; the inconvenience is one which society can afford to bear, for the sake of the greater good of human freedom. … But I cannot consent to argue the point as if society had no means of bringing its weaker members up to its ordinary standard of rational conduct, except waiting till they do something irrational, and then punishing them, legally or morally, for it. Society has had absolute power over them during all the early portion of their existence: it has had the whole period of childhood and nonage in which to try whether it could make them capable of rational conduct in life. The existing generation is master both of the training and the entire circumstances of the generation to come; it cannot indeed make them perfectly wise and good, because it is itself so lamentably deficient in goodness and wisdom; and its best efforts are not always, in individual cases, its most successful ones; but it is perfectly well able to make the rising generation, as a whole, as good as, and a little better than, itself. If society lets any considerable number of its members grow up mere children, incapable of being acted on by rational consideration of distant motives, society has itself to blame for the consequences. Armed not only with all the powers of education, but with the ascendancy which the authority of a received opinion always exercises over the minds who are least fitted to judge for themselves; and aided by the natural penalties which cannot be prevented from falling on those who incur the distaste or the contempt of those who know them; let not society pretend that it needs, besides all this, the power to issue commands and enforce obedience in the personal concerns of individuals, in which, on all principles of justice and policy, the decision ought to rest with those who are to abide the consequences.

In other words, society should fight self-destructive behavior with good education and child-rearing.