CHAPTER III
THE DESCENT OF MAN, AND OTHER BOOKS
When Darwin wrote the Origin of Species he considered it as little more than an abstract or outline of the subject, to be followed by a series of larger books giving in full the evidence for evolution which he possessed. One of these, "Variations of Animals and Plants under Domestication," he began on January 1, of 1860—less than six weeks after the publication of the Origin—but could not get on with it very rapidly. This partly was because of the great deal of work necessary to correct the successive editions of the Origin, but even more because of illness. At one time Darwin was unable to do anything for seven months, and shorter periods of disability were common. Also, conditions had shown that scientists were having trouble enough comprehending the preliminary book on evolution, so there was no pressing need for a series of larger treatises for a while, at least.
But perhaps the most important factor of all in the delay of the larger books was the great accumulation of data on lines other than evolution, which Darwin felt it his duty to publish. Thus as far back as 1839 he had begun to study the part which insects played in the cross-fertilization of flowers. Every summer he had devoted time to that work, and the accumulation of twenty years of investigation lay on his hands—valuable, indeed, yet doing no good
