The answer to every question

Recently I've been thinking about how the most recent research on human intelligence seems to indicate that it's decided more by nurture than by nature. Going by the latest studies, it seems that the biggest factor in a child's intellectual growth isn't anything genetic, it's the degree to which the child's mind was stimulated during the first few years of life. Kids whose parents talked to them and played with them a lot as babies tend to end up doing better on intelligence tests.

But the trouble with those studies is that it doesn't really mean anything conclusive when you prove that parents who stimulate their babies' minds end up having more intelligent children. You have to separate the environmental from the genetic: for all we know, the type of parents who do the best job at stimulating their children's minds might be the type of parents who have genes for intelligence, and maybe they're passing the intelligence on through genes rather than through mental stimulation.

To test this, you'd have to do a similar study on people with high IQs who had adopted infants biologically unrelated to them. If the adopted babies' intellectual growth responded in the same way to mental stimulation as that of biological children, you could be pretty sure that the connection was mostly nurture and not nature, and it would be another point against intelligence being mainly genetic.

Unfortunately, you couldn't make as conclusive a deduction if the adopted children's development did not follow that of the biological children, because one could argue that the adopted children's development was stunted by their time in the adoption system before being placed with the family, or that the family subconsciously did a poorer job of stimulating their minds because they loved them less than they would love a biological child. This is the trouble with the nature/nurture debate: it is very difficult to prove anything beyond a reasonable doubt. The only possible conclusive proof of genetic determinism would be if genes were found that were always associated with high intelligence, regardless of the environment in which one grew up.

However, I find that unlikely, because my own view of nature and nurture is that they're inextricably mixed up with each other. A lot of genes can be turned on or off by environmental factors, and some people seem more ruled by their biology than others, while some seem unable to overcome childhood experiences that shaped their personalities. I think making any blanket statement about what shapes human minds is foolish, because in nearly all cases it's a mix of factors, and individual cases can vary hugely in what part of that mix is most dominant, and how dominant that part is. Once again I have to come to my usual conclusion that the answer to every question is "it depends."