In Pursuit of the Gene

VIVA PANGENESIS © 11
Military College at Sandhurst that did. “There is, therefore, little room for
doubt,” he asserted, “if everybody in England had to work up some subject
and then to pass before examiners who employed similar figures of merit,
that their marks would be found to range, according to the law of deviation
from an average, just as rigorously as the heights of French conscripts, or
the circumferences of the chests of French soldiers.” 38
Although it was true that certain tests could be found to give a normal
distribution of scores, the equation of test scores with mental capacity remained
open to question. Nonetheless Galton forged ahead, using the assumption
of normality to divide the population into 14 groups, separated
by equal increments of “natural aptitude.” Arrayed to the right of center
were classes A, B, C, D, E, F, and G of increasing aptitude. To the left were
the mentally challenged, fittingly denoted in lowercase, a, b, c, d, e, f, and g.
The size of each class could be predicted by using the same table Quetelet
had used to find his theoretical values for height. Galton arranged the scale
so that the top two classes, F and G, combined would contain 1 in 4,000
men, which was his best estimate of the fraction of all educated men who
achieved eminence. He stretched for new poetic heights in order to explain
the extraordinary thing it was to be an F or a G: “On the most brilliant of
starlight nights there are never so many as 4,000 stars visible to the naked
eye at the same time; yet we feel it to be an extraordinary distinction to a
star to be accounted as the brightest in the sky.” 39
Despite the fact that he still had no solid basis for believing that intelligence
is analogous to height and chest size, Galton did not hesitate to apply
Quetelet’s reasoning to the mental realm. While reading Darwin’s theory of
pangenesis in the winter of 1868–69, Galton suddenly saw how Darwin’s hereditary
particles could be used to argue that intelligence, or any other
mental or physical trait, for that matter, would be normally distributed. As
he expressed it in a hastily composed concluding chapter of Hereditary Genius,
“It gives a key that unlocks every one of the hitherto unopened barriers to
our comprehension of [inheritance].” 40
In the simplest case, in which a trait was determined by two forms of a
particular gemmule that existed in equal numbers in each of the parents,
one would expect the trait to be normally distributed. If, for example, intelligence
depended on the inheritance of two forms of a gemmule, one that