organs, the consequences of which are that very _adaptation_ of the organism to external conditions, which is expressed as the _selection_ of the structures best adapted. The selections are the results of the struggle, according to my proposed extension of the term “struggle.” Mr. Darwin defines the struggle: “The dependence of one being on another, and including (what is more important) not only the life of the individual but success in leaving progeny.” This definition seems defective, since it omits the primary and more important struggle which takes place between the organic affinities in operation. To succeed in the struggle with competitors, the organism must have first acquired--by selection--a superiority in one or more of its organs. 118_f_. A little reflection will disclose the importance of keeping our eyes fixed on the internal causes of variation, as well as on the external conditions of the struggle. Mr. Darwin seems to imply that the external conditions which cause a variation are to be distinguished from the conditions which accumulate and perfect such variation, that is to say, he implies a radical difference between the process of variation and the process of selection. This, I have already said, does not seem to me acceptable; the selection, I conceive, to be simply the variation which has survived.[63] If it be true that a Variety is an incipient Species and shows us Species in formation, it is in the same sense true that a variation is an incipient organ. A species is the result of a slowly accumulating divergence of structure; an organ is the result of a slowly accumulating differentiation. At each stage of differentiation there has been a selection, but we cannot by any means say that this selection was determined by the fact of its giving the organism a superiority over rivals, inasmuch as during all the early stages, while the organ was still in formation, there could be no advantage accruing from it. One animal having teeth and claws developed will have a decided superiority in the struggle over another animal that has no teeth and claws; but so long as the teeth and claws are in an undeveloped state of mere preparation they confer no superiority.