What if we’ve been thinking about the genetics of intelligence
from completely the wrong angle? Intelligence (as indexed by IQ
or the general intelligence factor “g”) is clearly highly
heritable in humans – people who are more genetically similar
are also more similar in this factor. (Genetic variance has been
estimated as explaining ~75% of variance in g, depending on age
and other factors). There must therefore be genetic variants in
the population that affect intelligence – so far, so good. But
the search for such variants has, at its heart, an implicit
assumption: that these variants affect intelligence in a fairly
specific way – that they will occur in genes “for intelligence”.
An implication of that phrase is that mutations in those genes
were positively selected for at some stage in humanity’s descent
from our common ancestor with apes, on the basis of conferring
increased intelligence. This seems a fairly reasonable leap to
make – such genes must exist and, if variation in these genes in
humanity’s ev