So, as we’ve seen, IQ tests throw up a paradox.
On the one hand, twin studies suggest IQ is largely determined by genes. On the other, IQ scores have risen steadily over the decades in just about every country studied, including developing nations such as Kenya. This cannot possibly be genetic, so the environment must play a huge role.
Roger Lewontin suggested one answer. Imagine planting seeds in two different fields. One field might be richer than the other, so the average height of plants would be higher. The differences between plants in this field, however, would be entirely down to genes. In the second field, the average height might be lower, but again the differences between plants in the field would be entirely down to genetic variation.
The trouble with this idea is that no single environmental factor, such as better nutrition, can explain the rising IQ levels around the world. But what if the link between a child’s IQ and the environment it is exposed to isn’t random?
To explain this, imagine two sets of twins, one pair somewhat taller than average and the other somewhat shorter. Even if the tall twins are adopted by very different families, their height will give them an advantage in basketball. That might encourage them to practice more, making them better at the game, getting them into a better team, meaning they get better coaching, making them even better…
The opposite will be true for separated short twins. So if you were to do a standard twin study, you’d conclude that basketball skills are 100% genetic. Indeed, that’s what many scientists have concluded about intelligence on the basis of such studies.
In reality, what might be happening is that very small genetic differences in young children are being translated into a huge difference in adult abilities by determining what environment children are exposed to.
What’s more, these small initial differences are not necessarily even genetic. The children of a good basketball player could end up reaping the same amplifying effect of a small initial difference. It’s what William Dickens and James Flynn, after whom the Flynn effect is named, call social multipliers.
Flynn’s book What is intelligence? cites the emphasis on education in Chinese immigrant culture as the primary reason for the success of this group in the US. He sees their higher IQs as a result rather than a cause.
Equally, of course, an anti-intellectual culture will have the opposite effect.
So let’s go back to Watson’s claims. The idea that gene variants affecting intelligence differ between various groups of people is undoubtedly plausible. If Flynn is right, however, we haven’t even come close to proving this.
Flynn’s book is a bit self-indulgent, but anyone who thinks they know anything about IQ should read it before pontificating.