The Mismeasure of Man by Stephen Jay Gould

2l (^8) THE MISMEASURE OF MAN
near the top both in IQ and eminence. One might paraphrase Vol-
taire's famous quip about God and conclude that even though
adequate information on the IQ of history's eminent men does not
exist, it was probably inevitable that the American hereditarians
would try to invent it.
Terman on group differences
Terman's empirical work measured what statisticians call the
"within-group variance" of IQ—that is, the differences in scores
within single populations (all children in a school, for example). At
best, he was able to show that children testing well or poorly at a
young age generally maintain their ordering with respect to other
children as the population grows up. Terman ascribed most of
these differences to variation in biological endowment, without
much evidence beyond an assertion that all right-minded people
recognize the domination of nurture by nature. This brand of
hereditarianism might offend our present sensibilities with its
elitism and its accompanying proposals for institutional care and
forced abstinence from breeding, but it does not, by itself, entail
the more contentious claim for innate differences between groups.
Terman made this invalid extrapolation, as virtually all heredi-
tarians did and still do. He then compounded his error by confus-
ing the genesis of true pathologies with causes for variation in
normal behavior. We know, for example, that the mental retarda-
tion associated with Down's syndrome has its origin in a specific
genetic defect (an extra chromosome). But we cannot therefore
attribute the low IQ of many apparently normal children to an
innate biology. We might as well claim that all overweight people
can't help it because some very obese individuals can trace their
condition to hormonal imbalances. Terman's data on the stability
of ordering in IQ within groups of growing children relied largely
upon the persistently low IQ of biologically afflicted individuals,
despite Terman's attempt to bring all scores under the umbrella of
a normal curve (1916, pp. 65-67), and thus to suggest that all var-
iation has a common root in the possession of more or less of a
single substance. In short, it is invalid to extrapolate from variation
within a group to differences between groups. It is doubly invalid
to use the innate biology of pathological individuals as a basis for
ascribing normal variation within a group to inborn causes.
At least the IQ hereditarians did not follow their craniological