Darwin first began to be interested in the idea of modification by descent during his voyage on the Beagle and in the year 1837.[400] In his earlier years he had been satisfied with the conventionally orthodox theological and scientific conception of the creation of distinct species, and all his youthful work had been on the basis of this view. Such phrases as the note, written in 1834, in Valparaiso: ‘It seems not a very improbable conjecture that the want of animals may be owing to none having been created since this country was raised from the sea,’[401] are obviously significant of the earlier attitude. But as he observed more widely and became more and more impressed with the infinite diversity of forms and the delicacy of shading with which they pass into each other, the conviction grew that the possibilities of development were unlimited, and that individual differences might pass into varieties and these again into species, making the origin of varied life far simpler and more unified than had ever been imagined. And such an evolutionary process seemed much more in accord with general natural laws than the abrupt appearance of fixed, highly organized forms in sudden sufficiency. As he says, ‘the subject haunted me,’ and from a very early period he began making notes and memoranda of all observations that might bear for—or against—the gradual modification of species. [Illustration: A PAGE FROM A NOTEBOOK OF 1837] The difficulty was to imagine just how the process of modification was brought about, and until he could get some light on this point, his enthusiasm for the general idea was chilled and baffled. As we have seen, Lamarck’s view, that living beings directly adapted themselves to their surroundings and then transmitted these adaptations to their descendants, seemed at least inadequate, and Darwin felt that the theory must have some more solid basis, if it was to prevail at all. He set his mind to work for months and months, and he applied the intellectual method which he himself has so admirably defined in a letter to his young son: ‘I have been speculating last night what makes a man a discoverer of undiscovered things; and a most perplexing problem it is. Many men who are very clever—much cleverer than the discoverers—never originate anything. As far as I can conjecture, the art consists in habitually searching for the causes and meaning of everything which occurs.’[402]