In the other paragraph, Darwin presented his own brief summary of Jenkin’s swamping argument. This paragraph is fascinating because of two apparently small yet extremely significant differences from Jenkin’s original text. First, Darwin assumes here that a pair of animals has two hundred offspring, of which two survive to reproduce. In spite of his nonmathematical background, therefore, Darwin appears to have anticipated already in 1869 the correction to Jenkin pointed out in A. S. Davis’s letter to Nature in 1871: For the population not to disappear, two offspring, on the average, must survive. Second, and even more intriguing, Darwin assumes in his summary that only half of the offspring of the “sport” inherit the favorable variation. Note, however, that this assumption is contrary to the predictions of blending heredity! Unfortunately, Darwin was still unable at that time to elaborate on the possible consequences of a nonblending theory of heredity, and he accepted Jenkin’s conclusions without any further discussion.

There are, nevertheless, quite a few signs that Darwin had not been happy with blending heredity for quite a while. In a letter he wrote in 1857 to the biologist Thomas Henry Huxley, his friend and champion in the public arena, he explained:

Approaching the subject [of evolution] from the side which attracts me most, viz inheritance, I have lately been inclined to speculate very crudely and indistinctly, that propagation by true fertilization, will turn out to be a sort of mixture and not true fusion, of two distinct individuals, or rather innumerable individuals, as each parent has its parents and ancestors. I can understand on no other view the way in which crossed forms go back to so large an extent to ancestral forms. But all this, of course, is infinitely crude.

Crude or not, this observation was extremely insightful. Darwin recognized here that the combination of paternal and maternal heredity material was more like the shuffling together of two packs of cards rather than like the mixing of paints.

While Darwin’s ideas in this letter can definitely be considered impressive forerunners of Mendelian genetics, Darwin was eventually driven by his frustration with blending heredity to develop a completely wrong theory known as pangenesis. In Darwin’s pangenesis, the entire body was supposed to issue instructions to the reproductive cells. “I assume,” he wrote in his book The Variation of Animals and Plants Under Domestication,