In Pursuit of the Gene

36 ¨ REVERSION TO THE MEAN
hereditary transmission, “a simple and far-reaching law,” as he later described
it. 34
The phenomenon of reversion to the mean raised an interesting paradox,
which Galton illustrated by considering the case of gigantism. The
principle of reversion implied that exceptionally tall people would tend to
have somewhat shorter children, and therefore the expectation would be
that the relative number of “giants” ought to decrease over time. However,
it was clear that the fraction of giants in successive generations remained
more or less constant. Two winters after he’d first begun analyzing his pea
data, Galton believed he had successfully resolved the apparent paradox. In
his grand style, Galton introduced his new theory in a well-publicized
lecture delivered in the theater of the Royal Institute in February 1877. By
tradition, the men in the audience wore evening dress and the women
were done up in their finest gowns.
Preparation of the lecture, subsequently published in three parts in Nature,
had required painstaking work. As early as the spring of 1876, Galton
had sent the manuscript to Darwin’s son George for his comments on a
preliminary draft. Its unprepossessing title was “Experiments with Plants
and the Causes of Statistical Uniformity in Successive Generations.” George,
the most mathematically inclined of Darwin’s sons, had found the manuscript
too obscure and advised a total rewrite, a setback Galton took in
stride: “These confounded law of error ideas, which in themselves are so
simple and clear but to express which no proper language exists and which
lies so completely out of the everyday lines of thought are very baffling to
deal with and to present, but I don’t despair yet.” 35
By January 1877, Galton completed a new, totally revised draft. But the
revision still did not earn George’s approval. “I am aghast at the trouble my
unlucky memoir gives,” Galton apologized, promising to undertake yet a
third rewrite. 36 The final version of the paper presented a highly contrived
model that attempted to reconcile the fact that children tended to revert
to the mean with the fact that variability was not actually lost over successive
generations. 37 Galton did not even mention the pea data. As he explained
a decade later, this data had been so beset by inconsistencies and ir-