I was reading an article in some American newspaper, where one of the comments some man made was that he believed ‘all IQ variations were due to environment’…
Which didn’t half make me laugh my socks off. If that were the case it would be possible to train a cat to beat Bobby Fischer at chess by raising it in a well to do middle class environment. It’s a very common belief. It’s very socialist too. But wrong. Barring one Russian study, the consensus is that the the heritability of IQ increases with age. Sorting the results by age suggests that heritability increases from ~20% in infancy to ~40% in childhood, to 60% later in life (McGue et al. 1993), even for individuals 80 years of age .(McClearn et al. 1997).
To extend this quote, the ‘later in life’ means late adolescence. Once you’re properly adult you’re looking at about 70% inheritable.
This heritability varies with environment. If you are malnourished your body will never reach its full height, and illnesses can have the same effect. A very bad environment will lower the heritability of IQ, and this will be most apparent in children from very abusive homes, where they are beaten and starved and denied an education. Expecting genetics to win in that situation is ridiculous. But the vast majority of the Western world have enough, and usually more than enough, to eat. The television blares vocabulary and new concepts at us, even if we don’t go to school. Most of us didn’t routinely fend off an abusive fist or get given hard drugs as children. For the majority of people in the West, genes decide how smart we are.