THE HEREDITARIA N THEORY OF IQ
impressed upon me by the studies of so many other scientists, that
intellectual superiority is tied to superiority of cerebral volume"
(1900, p. 427).
Binet found his differences, but they were much too small to
matter and might only record the greater average height of better
pupils (1.401 vs. 1.378 meters). Most measures did favor the better
students, but the average difference between good and poor
amounted to a mere millimeter—"extremement petite" as Binet wrote.
Binet did not observe larger differences in the anterior region of
the skull, where the seat of higher intelligence supposedly lay, and
where Broca had always found greatest disparity between superior
and less fortunate people. To make matters worse, some measures
usually judged crucial in the assessment of mental worth favored
the poorer pupils—for anteroposterior diameter of the skull,
poorer students exceeded their smarter colleagues by 3.0 mm.
Even if most results tended to run in the "right" direction, the
method was surely useless for assessing individuals. The differ-
ences were too small, and Binet also found that poor students var-
ied more than their smarter counterparts. Thus, although the
smallest value usually belonged to a poor pupil, the highest often
did as well.
Binet also fueled his own doubts with an extraordinary study
of his own suggestibility, an experiment in the primary theme of
this book—the tenacity of unconscious bias and the surprising
malleability of "objective," quantitative data in the interest of a pre-
conceived idea. "I feared," Binet wrote (1900, p. 323), "that in
making measurements on heads with the intention of finding a dif-
ference in volume between an intelligent and a less intelligent
head, I would be led to increase, unconsciously and in good faith,
the cephalic volume of intelligent heads and to decrease that of
unintelligent heads." He recognized the greater danger lurking
when biases are submerged and a scientist believes in his own
objectivity (1900, p. 324): "Suggestibility... works less on an act of
which we have full consciousness, than on a half-conscious act—
and this is precisely its danger."
How much better off we would be if all scientists submitted
themselves to self-scrutiny in so forthright a fashion: "I want to
state very explicitly," Binet wrote (1900, p. 324), "what I have
observed about myself. The details that follow are those that the