statements and arguments with fatal flaws in them are made by writers who express themselves easily, than by writers whose rhetorical inability compels them to be painstaking. When the expression is laboriously evolved by an intellect that is otherwise strong, the thought comes during the process to be regarded from more points of view. In details there is greater assurance of accuracy, and the proper relative importance is more likely to be assigned to the different phases of the truth. Given two intellects equally conscientious, the slower moving and more deliberate one will always hit upon more phases of the truth than the quicker one. Darwin attributed the success of the "Origin of Species" to the way in which it was developed. Only when he had spent a number of years in investigation, after he had got hold of the theory of natural selection, did he allow himself, in 1842, to draw up a brief thirty-five page sketch of it. In 1844 he wrote a larger sketch of two hundred and thirty pages. Then followed years of laborious investigation, the vast results of which were cast into an abstract which, if it had been published, would have been a very large work. Upon the urgent advice of his friends, Lyell and Hooker, he decided not to delay publication any longer;

but the large work was not in condition for publication. An abstract of it was made; and this abstract was the "Origin of Species." He had written two condensed sketches, and finally abstracted a much larger manuscript which was itself an abstract.1 Probably no work was ever better tempered and tested before it reached. the public eye.

1 Life and Letters, Vol. I. p. 70.

XV.

LOGICAL HISTORY OF THE PRINCIPLE OF NATURAL SELECTION.

ARWIN'S own views of method, his treat

DAR

ment of evidence, and some of the various logical processes which he employed in his investigations, having been discussed and illustrated by examples from his many works, it now remains necessary to trace the logical history and examine the present logical status of the principle of natural selection, which gave inspiration to and lay at the basis of his lifework. The theory of natural selection has permeated and colored modern thought more deeply than perhaps any other scientific theory, and this fact alone makes the study of its logical history extremely interesting.

The scientific influences, both in the form of teachers and of books, to which Darwin was exposed during and after his university life, were opposed to the already well known doctrine of the descent of species. Various reasons have been assigned for the failure of the doc

trine to impress itself upon scientific men. The difficulty did not lie in the circumstance. that the facts of botany and zoology were opposed to it; for it first took its rise out of them. The affinities of species and of the higher groups, and the facts of embryology, distribution, and palæontology by themselves were sufficient to force the conviction that species are derived, and the doctrine would doubtless have won its way at once had it not had to make head against the imported belief in creation. Had the doctrines of descent and creation been for the first time presented to the scientific mind as alternative beliefs, there can be no doubt that the former would have been chosen as the true explanation of the facts, even though no force capable of producing the effects had been assigned. The cause would still remain to be investigated, while the facts would be brought together under a single point of view. With the adoption of creation as an explanation, an efficient cause is provided, but the facts remain worthless either to prove or to disprove the doctrine. It is not enough that a cause should be capable of producing given effects, but it should produce the given effects and be incapable of producing any other set of effects. In short, by the former view the

special character of the facts is accounted for, but from the latter it is impossible to deduce the specific character of any phenomena. Any other set of facts exhibiting a plan or purpose of any kind could be deduced with equal ease from the doctrine of creation.

When Darwin started on the Beagle voyage he was orthodox on the question of the origin of species. As he travelled, and as his knowledge of zoology and palæontology became wider and deeper, the doctrine of descent began to take hold of him. The relation of the living animals to the fossil species in South America, the manner in which closely allied animals replaced one another as he proceeded southward over the continent, the South American character of the productions of the Galapagos archipelago, and especially the slight but distinct differences of the flora and fauna on neighboring islands of the archipelago, impressed him so strongly with the peculiar character of the facts and the necessity of a definite mode of origin that he began to see the difference in the logical characters of the doctrines of creation and descent.1 The facts were better explained by the latter than by the former; and he connected them at least tentatively with the 1 Life and Letters, Vol. I. p. 67; Origin of Species, p. 2.