Genes, Brains, and Human Potential The Science and Ideology of Intelligence

66 PRETEND GENES

estimates should be abandoned. Th ey are based on false ge ne tic and en-

vironmental premises and are fatally fl awed methodologically.

AN ALTERNATIVE TO TWIN STUDIES?

As mentioned in chapter 1, gene- sequencing studies have found no reliable
associations between gene variants (SNPs) and mea sures of intelligence.
So there is currently widespread dismay at this “missing heritability”
prob lem. Instead of seriously considering the possibility that these are
artifacts of the fl aws in the twin method, however, behavioral ge ne ticists
have sought other ways to rescue their preconceptions.
Th e main argument is that the genes are not really missing. Th at is, the
heritability must be the result, they suggest, of hundreds or thousands of
genes, each making an infi nitesimal diff erence, too small to be detected
by the DNA sequencing methods. Th eir single eff ects on individual dif-
ferences in potential are vanishingly small, they argue, but collectively
they are still there, just as the twin studies suggest.
So a new and convoluted method has been devised to support that
idea. Although involving numerous statistical maneuvers and yet more
assumptions, behavioral ge ne ticists have been very excited about it. So
convinced are authors like Ian Deary and colleagues of its fl awlessness
that they claimed it established and unequivocally confi rmed previous
results.^36 Th ese are terms not widely (or wisely) used in science.
Th e new method involves sequencing the genomes of thousands of
individuals. Th at identifi es which version of each variable SNP (i.e., the
component letters in the ge ne tic words) each individual actually has. Th e
degree of ge ne tic correlation between each and every pair of individuals
in the sample is then computed. Th eir IQ correlations are also computed.
And the correlation between the two correlations is computed, leading to
an estimate of heritability. Th e method is called genome- wide complex
trait analy sis (GCTA).
Unfortunately, the method entails a formidable battery of assumptions,
data corrections, and statistical maneuvers. One of these is the assump-
tion of genes (and SNPs) as in de pen dent units, as just mentioned. Another
is that (as usual in this fi eld) all correlations are taken, without further

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