52 PRETEND GENESTh e statistical models must assume randomized mating. Th at is, par-
ents do not select one another by compatibility of perceived mental traits,
or anything else (called assortative mating); instead, they select one
another randomly, like names out of a hat. But this assumption is most
obviously false. In their 2015 article in the journal Molecular Psychiatry,
Robert Plomin and Ian Deary note that IQ correlations between spouses
is around 0.4, and is greater for intelligence (i.e., IQ scores or some ap-
proximation of it) than any other behavioral trait.^12
Th e statistical model also assumes that there has been no natu ral
se lection for human potential. Th is assumption implies that plenty of
variable genes are randomly spread across individuals in the species. In
real ity, it is a logical consequence of natu ral se lection that traits impor-
tant to survival have usually been through intense se lection. Th is implies
progressive reduction in ge ne tic variation and heritability across genera-
tions as deleterious alleles are eliminated (the bearers fail to reproduce).
I return to this below.
Th ere is also the assumption that the genes, in passing from parents to
off spring, do so as random collections of in de pen dent units. In fact this
is known to be unlikely, especially for genes that have been subjected to
natu ral se lection and that form integrated (i.e., linked) sets or are close
to each other on chromosomes.
A NAÏVE MODEL KNOWN TO BE FALSEAll these assumptions are known to be false. As a consequence, heritabil-
ity estimates based on them are likely to be distorted. Th e strange thing
is that those who make loud claims about the ge ne tics of intelligence also
know that the assumptions are false. Occasionally they admit it. Th is was
indicated in the quote from Burt and Howard cited above. In a 2007 paper
in the same tradition, Wendy Johnson admitted that one of their model-
fi tting assumptions (random mating) is “contrary to evidence” and that
other assumptions “are generally oversimplifi cations of the actual situation,
and their violation can introduce systematic distortions and estimates.”^13
In sum, the in de pen dent/additive model— the basis of nearly all pro-
nouncements (to scientists, governments, or the general public) about the
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