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

74 PRETEND INTELLIGENCE

course huff and puff that this is not true and insist that they are mea sur-

ing impor tant cognitive diff erences in children and adults. Th ey point

to correlations with school per for mance, job status, and earnings. But

the fact is that intelligence testing is another game of let’s pretend, quite

diff er ent from ordinary scientifi c mea sure ment.

In scientifi c method, and in medicine, we do oft en need to take or

infer diff erences in some observable variable as a mea sure of an internal

function. But we only do that if we can mechanistically (causally) relate

diff erences in one to diff erences in the other. For example, we can dem-

onstrate why the height of a column of mercury (or digital readout) in a

blood pressure machine will genuinely co- vary with the pressure of blood

in the arteries. Likewise, we know why a white blood cell count is an in-

dex of levels of internal infection, why erythrocyte sedimentation rate is

a reasonable mea sure of tissue infl ammation, and why degree of breath

alcohol corresponds fairly accurately with level of consumption.

Such mea sures are said to be valid because they rely on detailed, and

widely accepted, theoretical models of the functions in question. In each

case, diff erences in the mea sure truly correspond with diff erences in the

internal function, and we know why. Th ere is no such theoretical basis

for human intelligence nor, therefore, for the true nature of individual

diff erences in it. Diff erences in IQ cannot be reliably related to such in-

ternal functions. Instead, they are calibrated against some other diff erences

of individuals, also assumed to refl ect diff erences in intelligence. Th at is

how IQ testing operates.

So how can we purport to be mea sur ing impor tant cognitive func-

tions with an IQ test? And, if it is not mea sur ing cognitive functions,

what is it mea sur ing? To answer those questions, we need to look back quite

a long way.

IDEOLOGICAL ORIGINS

Th e pretense started with Sir Francis Galton, cousin of Charles Darwin,
in late Victorian Britain. As mentioned in chapter 1, Galton proposed a
eugenic, or selective, breeding program for the intellectual improvement
of society. And that required a scientifi c mea sure ment of ability “for the

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