PRETEND GENES 53importance of genes— seems to be the solution to another spherical horse
prob lem. Th is is why critics like Stig Omholt complain of “the abyss that
currently exists between quantitative ge ne tics theory and regulatory
biology.”^14 Th e only reasonable conclusion is that if the behavioral ge ne-
ticists’ data fi t such unlikely models, there must be something seriously
wrong with the data, the interpretation of them, or both. So now let us
look at those data.
THE “GE NE TIC” DATATh e logic of behavioral ge ne tics indicates that the ideal sources of infer-
ences are pairs of twins. In the case of IQ, the degree of IQ resemblance
among such pairs should, the logic says, be an indication of the impor-
tance of ge ne tic resemblances and therefore of ge ne tic diff erences (assum-
ing that IQ is a mea sure of human intelligence; see chapter 3). Th ere have
been two main types of study.
Twins Reared Apart
Th e existence of separated identical twins has been seized on as a con ve-
nient natu ral experiment for the direct estimation of heritability in
humans. Th e average degree of resemblance between pairs must refl ect
their shared genes, because they have not shared environments—or so it
is argued.
Th ere have been a number of such studies since the 1930s. I mentioned
above how Burt’s study is now disregarded because of suspected fabrica-
tion of data. Th e most famous study by far is the Minnesota Study of
Twins Reared Apart (MISTRA), conducted since the 1970s by Th omas
Bouchard and colleagues. Th eir fi rst major publication was in 1990 in the
prestigious journal Science. Th ey began by saying, “Monozygotic and
dizygotic twins who were separated early in life and reared apart (MZA
and DZA twin pairs) are a fascinating experiment of nature. Th ey also pro-
vide the simplest and most power ful method for disentangling the infl u-
ence of environmental and ge ne tic factors on human characteristics.”
Th ey conclude that the MZA correlation “directly assesses heritability.”^15
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