My latest Mind and Matter column in the Wall Street Journal:
Hardly any subject in science has been so politically fraught as the heritability of intelligence. For more than a century, since Francis Galton first started speculating about the similarities of twins, nature-nurture was a war with a stalemated front and intelligence was its Verdun-the most hotly contested and costly battle.
The genes for intelligence are there, but there are thousands of them and each has only a tiny impact.
So would it not be rather wonderful if a scientific discovery came along that called a truce and calmed all the fury? I think this is about to happen. Call it the Goldilocks theory of intelligence: not too genetic, not too environmental-and proving that intelligence is impossible to meddle with, genetically.
The immediate cause of this optimism is arecent paper in Molecular Psychiatry, which confirms that genes account for about half of the difference in IQ between any two people in a modern society, but that the relevant genes are very numerous and the effect of each is very small.
There has always been a gap between the emphatic conclusions of the behavior geneticists studying twins and adoptees-yes, genes matter very much-and the equally emphatic conclusions of the molecular biologists using tools like quantitative trait analysis: No, we cannot find any particular genes that vary in concert with IQ.
It turns out the genetic differences may have been all just below the measurement radar. A new technique, which can now detect very slight genetic influences, has succeeded where the old techniques failed. The genes for intelligence are there, but there are thousands of them and each has only a tiny impact. To be clever you must have a good combination of the clever versions of lots and lots of genes. There is an evolutionary reason for this: Any gene difference with big effect is going to get grabbed by natural selection and quickly turned into a universal trait.
So the old terror, which so alarmed many psychologists and educationalists, that one day people-or governments-would use genes to decide whom to kill, sterilize or prevent being born because of their intelligence, suddenly looks a lot less scary. There are just too many genes.
People, and governments, did kill, sterilize and prevent people being born, for sure, but they were never able to use specific genes to justify their unscientific theories. In other words, it was ignorance about genetics, not knowledge of genetics, that made eugenics possible.
To be clever you must have a good combination of the clever versions of lots and lots of genes.
Nor is this the only happy outcome of intelligence research. Some of the more extreme "nurturists," especially those who dominated the debate in the 1960s to 1980s, might not welcome the new confirmation of the nearly 50% role of genes in determining IQ differences, even though it has been blindingly clear for a long time now.
They should, though. A world in which intelligence is 100% genetic would be horribly unfair. But so would a world in which intelligence is 100% environmental. Think what it says about education: Bad luck, you went to a poor school, or had dud teachers, or neglectful parents, so you can never be clever. For an aspirational, meritocratic society, in which people can thrive despite their disadvantaged start, there absolutely must be a genetic element to talents of all kinds, but it must not be too big.
Intriguingly, the heritability of intelligence has probably been increasing in recent decades. The more we make sure everybody gets sufficient nutrition and education, the less these factors will determine differences in outcome, so the more differences in genes will determine the differences that remain. The fairer society becomes, the higher heritability will be.
The new results are just right for proving that education is not futile, but nor is it a life sentence. And that the genes that matter are so many and so slight in their impact that seeking them out for your children through genetic engineering will never be practical anyway. Now, isn't that a happy result?