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My latest Mind and Matter column in the Wall
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
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
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
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
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
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?