It was Professor Henslow who secured for young Darwin the appointment of naturalist to the voyage of the “Beagle.”  This voyage lasted from Dec. 27, 1831, to Oct. 2, 1836.  The incidents of this voyage will be found set forth in Darwin’s “Public Journeys.”  The observations made by him in geology, natural history, and botany gave him a place of considerable distinction among scientific men.  In 1844 he published a series of observations on the volcanic islands visited during the voyage of the “Beagle,” and two years later “Geological Observations on South America.”  These two books, together with a volume entitled “Coral Reefs,” required four and a half years’ steady work.  In October, 1846, he began the studies embodied in “Cirripedia” (barnacles).  The outcome of these studies was published in two thick volumes.  The time came when Darwin doubted whether the work was worth the consumption of the time employed, but probably it proved of use to him when he had to discuss in the “Origin of Species” the principles of a natural classification.  From September, 1854, and during the four ensuing years, Darwin devoted himself to observing and experimenting in relation to the transmutation of species, and in arranging a huge pile of notes upon the subject.  As early as October, 1838, it had occurred to him as probable, or at least possible, that amid the struggle for existence which everywhere goes on in the animal world, favorable variations would tend to be preserved, and unfavorable ones to be destroyed.  The result would be the formation of new species.

It was not until June, 1842, however, that Darwin allowed himself the satisfaction of writing a very brief abstract of his theory in thirty-five pages.  This was enlarged two years later into one of 230 pages.  Early in 1856, Sir Charles Lyell, the well-known geologist, advised him to write out his views upon the subject fully, and Darwin began to do so on a scale three or four times as extensive as that which was afterwards followed in his “Origin of Species.”  He got through about half the work on this scale.  His plans were overthrown, owing to the curious circumstance that, in the summer of 1858, Mr. Alfred E. Wallace, who was then in the Malay archipelago, sent him an essay “On the Tendency of Varieties to depart indefinitely from the Original Type.”  It turned out upon perusal that this essay contained exactly the same theory as that which Darwin was engaged in elaborating.  Mr. Wallace expressed the wish that, if Darwin thought well of the essay, he should send it to Lyell.  It was Sir Charles Lyell and Sir Joseph Hooker who insisted that Darwin should allow an abstract from his manuscript, together with a letter to Prof.  Asa Gray, dated Sept. 5, 1857, to be published at the same time with Wallace’s essay.  Darwin was unwilling to take this course, being then unacquainted with Mr. Wallace’s generous disposition.  As a matter of fact, the joint productions excited very little attention, and the only published notice of them asserted that what was new in them was false, and that what was true was old.  From the indifference evinced to the papers which first propounded the theory of natural selection, Darwin drew the inference that it is necessary for any new view to be explained at considerable length in order to obtain the public ear.