In the letters written even in boyhood we see foreshadowed the direction and extent of his future researches. "Exactly what he determined in youth to accomplish," says Dr John Todhunter in his Preface to Harvey's _Memoir_, "he accomplished; the work which he took upon himself to do he did, honestly and thoroughly; the fame which he desired to achieve, he achieved." He saw that his strength lay in discrimination, description, and illustration, and to these--the necessary census task which forms the groundwork on which great theories may be built up--he confined himself. The latter years of his life fell within that stimulating period which followed the publication of Darwin's _Origin of Species_. But in the battle of giants which ensued he took no part. His attitude, indeed, was rather that of an amused spectator; and in the letters which are available, his references to the great controversy of the day, and allied topics, are mostly in a playful vein. "I do not know how cats purr," he writes to his friend Mrs Gatty, "and am glad you asked.... Have you never felt a something stop your own windpipe when pleased or grieved, when suddenly affected either way? 'Tis the first gurgle of a purr; you were a cat once, away in the ages, and this is a part of the remains." Almost his only contribution to the literature of natural selection was a "serio-comic squib," which was read before the Dublin University Zoological and Botanical Association on 17 February, 1860 and subsequently printed for private circulation, entitled "A Guess as to the Probable Origin of the Human Animal considered by the light of Mr Darwin's Theory of Natural Selection, and in opposition to Lamarck's notion of a Monkey Parentage." Darwin thought this production a little unworthy of the author. "I am not sorry for a natural opportunity of writing to Harvey," he says, "just to show that I was not piqued at his turning me and my book into ridicule, not that I think it was a proceeding that I deserved, or worthy of him[115]." Similarly, Harvey rejoices over Charles Kingsley's _Water Babies_, and especially over the sly fun which is poked at Darwinism, and also at certain types of men of science. Only once did he enter the lists with a serious criticism, when, in the _Gardeners' Chronicle_[116], he cites the case of a monstrous Begonia in objection to Darwin's views. Harvey, indeed, did not like the new theory. "I am fully disposed to admit natural selection as a _vera causa_ of much change," he writes, "but not as the _vera causa_ of species." Further than this he could not go, though much impressed with the arguments drawn from geographical distribution. "I heartily wish we were nearer in accord," writes Darwin at the end of a long letter to Harvey, "but we must remain content to be as wide asunder as the poles, but without, thank God, any malice or other ill-feeling[117]."