3. If the time of reaching maturity in the new form is different from that in the parent forms, then the new species will be kept from crossing with the parent form, and since this new character will be present from the beginning, the new form will have much better chances of surviving than if a difference in time of reaching maturity had to be gradually acquired. 4. The new species that appear may be in some cases already adapted to live, in a different environment from that occupied by the parent form; and if so, it will be isolated from the beginning, which will be an advantage in avoiding the bad effects of intercrossing. 5. It is well known that the differences between related species consists largely in differences of unimportant organs, and this is in harmony with the mutation theory, but one of the real difficulties of the selection theory. 6. Useless or even slightly injurious characters may appear as mutations, and if they do not seriously affect the perpetuation of the race, they may persist. In Chapters X and XI, an attempt will be made to point out in detail the advantages which the mutation theory has over the Darwinian theory. ------------------------------------------------------------------------ CHAPTER IX EVOLUTION AS THE RESULT OF EXTERNAL AND INTERNAL FACTORS We come now to a consideration of other theories that have been advanced to account for the evolution of new forms; and in so far as these new forms are adapted to their environment, the theories will bear directly on the question of the origin of adaptive variations. One school of transformationists has made the external world and the changes taking place in it the source of new variations. Another school believes that the changes arise within the organism itself. We may examine these two points of view in turn. The Effect of External Influences We have already seen that Lamarck held as a part of his doctrine of transformation that the changes in the external world, the environment, bring about, directly, changes in the organism, and he believed that all plants and many of the lower animals have evolved as the result of a reaction of this sort. This idea did not originate with Lamarck, however, since before him Buffon had advanced the same hypothesis, and there cannot be much doubt that Lamarck borrowed from his patron, Buffon, this part of his theory of evolution.