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

190 HOW THE BRAIN MAKES POTENTIAL

deeply aff ect perceptions, cognitions, and be hav iors, as well as physiol-

ogy and epige ne tics. Th ose emotional values can in turn be the source of

large individual diff erences in response to challenging situations, such as

cognitive and educational tests (of which more in chapter 10). Just feeling

inferior, or thinking that others might think of you as inferior, can have

devastating eff ects on cognitive per for mance. Again, this is rarely if ever

considered in the simple linear determinism (genes → brains → intelligence

diff erences) that dominates the lit er a ture.

INDIVIDUAL DIFFERENCES

So now let us briefl y consider the implications of all this for the descrip-
tion and mea sure ment of individual diff erences in human brains and the
possibility of correlating those with diff erences in intelligence. (Th e ac-
count here is brief, because I elaborate much more on this issue in
chapters 10 and 11).
Unfortunately, studies in the area have been founded on the old view
of ranked brains and mechanical meta phors: that individual diff erences
in ability stem from diff erences in constitutional aspects of the brain-
machine. Th is has meant using meta phors of “brain power”— capacity,
size, speed, effi ciency, or whatever—as criteria of ability, and always on
the assumption they fall into simple ranks in normal distributions deter-
mined by the chance permutations of genes.
I mentioned earlier James Flynn’s reference to “ge ne tic potential for
a better- engineered brain” with likeness to a “high- performance sports
car.” But such allusions are quite widespread. An article by Kenia Marti-
nez and colleagues in the journal Brain Mapping (2015) says that some
individuals are more cognitively effi cient than others. Ian Deary sees
brain functions as having more or less “biological fi tness” (refl ecting a
kind of Darwinian survival- of- the- fi ttest race to be fi rst).
Almost all these attempts have taken IQ- like mea sures and some
quantitative mea sure of (assumed) brain structure or function, and
looked for correlations between them. Eff orts to correlate intelligence
with brain size, for example, were started in the nineteenth century. But
the methods were acknowledged to be crude and inaccurate. In the past

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