Published on:

Paradoxical features of the genetics of intelligence

My fellow Times writer the
cricketer Ed Smith posed me a very good question the other day. How
many of the people born in the world in 1756 could have become
Mozart? (My answer, by the way, was four.) So here’s a similar
question: how many Britons born in 1964, if educated at Eton and
Balliol, could have achieved what Boris Johnson has achieved? It’s
clearly not all of them; it’s probably not one; but it’s not a big

My point? There is little doubt that Boris Johnson is a highly
intelligent man, notwithstanding his inability to cope with a radio
ambush of IQ test questions, and that he would be a highly
intelligent man even if he had not gone to Eton and Balliol —
barring extreme deprivation or injury.

The recent burst of interest in IQ, sparked first by Dominic
Cummings (Michael Gove’s adviser), and then by Boris, has been
encouraging in one sense. As Robert Plomin, probably the world’s
leading expert on the genetics of intelligence, put it to me, there
used to be a kneejerk reaction along the lines of “you can’t
measure intelligence”, or “it couldn’t possibly be genetic”. This
time the tone is more like: “Of course, there is some genetic
influence on intelligence but . . .”

The evidence from twin studies, adoption studies and even from DNA evidence is relentlessly consistent: in children, in
Western society, the heritability of IQ scores is about 50 per
cent. The other half comes equally from family (shared environment)
and from unshared individual experiences: luck, teachers,

This numerical precision easily misleads us into thinking genes
and environment struggle against each other. In fact, they are like
two pillars supporting an arch: nature makes you seek out nurture,
which brings out your nature. But here is where things get
interesting. The acceptance of genetic influence on intelligence
leads to some surprising, even paradoxical implications, some of
which turn the assumptions of both the Right and the Left upside

First, if intelligence was not substantially genetic, there
would be no point in widening access to universities, or in grammar
schools and bursaries at private schools trying to seek out those
from modest backgrounds who have more to offer. If nurture were
everything, kids unlucky enough to have been to poor schools would
have irredeemably poor minds, which is nonsense. The bitter irony
of the nature-nurture wars of the 20th century was that a world
where nurture was everything would be horribly more cruel than one
where nature allowed people to escape their disadvantages.

The Left, which has championed nurture against nature, is
learning to take a different view — over homosexuality, for
example, or learning disability, genetic influence is used as an
argument for tolerance. A recent Guardian headline
criticised Boris by saying “gifted children are failed by the
system”, which presupposes the existence of (genetically) gifted

The second surprise is that genetic influence increases with age. If you measure the
correlation between the IQs of identical twins and compare it with
that of adopted siblings, you find the difference grows
dramatically as they get older. This is chiefly because families shape the
environments of young children, whereas older children and adults
select and evoke environments that suit their innate preferences,
reinforcing nature.

[See the new paper by Briley, D. A. , &
Tucker-Drob, E. M. (in press). Explaining the
increasing heritability of cognitive ability over development: A
meta-analysis of longitudinal twin and adoption studies.
Psychological Science.]

It follows — the third surprise — that much of what we call the
“environment” proves to be itself under genetic influence. Children
who are very good at reading are likely to have parents who read a
lot, schools that give them special opportunities and friends who
recommend books. They create a reading-friendly environment for
themselves. The well-documented association between family
socio-economic status and IQ, routinely interpreted as an
environmental effect, is, writes Professor Plomin and colleagues,
“substantially mediated by genetic factors”. Perhaps intelligence is an appetite, at least much as
an aptitude, for learning.

The fourth surprise is that the better the economy, education,
and welfare are, the more heritable IQ will be. Just as having
extra food will make you brighter if you are starving, but not if
you are plump, so the same applies to toys, teachers, books and
friends. Once you have enough of any of these things, having more
will not make as much difference. So differences due to environment
will fade. In a world when some are starving and some are kings,
the differences would be mainly environmental. In a world where all
went to Balliol, the main difference remaining would be genetic.
Social reformers rarely face this fact — the more we equalise
opportunity, the more the people who get to the top will be the
genetically talented.

And this brings a final paradox: a world with perfect social
mobility would show very high heritability. The children of Balliol
parents would qualify for Balliol disproportionately, having
inherited both aptitude and an appetite for evoking the
environments that amplified that aptitude. Far from indicating that
parents are giving their children unfair environmental advantages,
a high correlation between the achievements of parents and
offspring suggests that opportunity is being levelled, albeit
slowly and patchily. In Professor Plomin’s words: “Heritability can
be viewed as an index of meritocratic social mobility.”

Moreover, assortative mating is probably reinforcing the trend.
That is to say, 50 years ago, when women were not often allowed
near higher education, Professor Branestawm chose to marry the girl
next door because she was good at ironing his shirts, whereas today
he marries another professor because she writes gorgeous equations
about quantum mechanics, and they have children who are professors

We are a long way from equality of opportunity, but when we get
there we will not find equality of outcome. Already IQ — for all
its flaws as an objective measure of intelligence — is good at
predicting not just educational attainment, but income, health and
even longevity remarkably well.

Do we reconcile ourselves to inequality, then? No! Just because
capability is inherited does not mean it is immutable. Hair colour
and short sight are highly heritable , but both can be altered.
Education is not just about coaxing native wit from the gifted, but
also coaching it into the less gifted.

By Matt Ridley | Tagged:  rational-optimist  the-times