We may conveniently summarize what we have said in the foregoing chapters in the following statement: The theory of Descent is almost universally recognized to-day by naturalists as a working hypothesis. Still, in spite of assertions to the contrary, no conclusive proof of it has as yet been forthcoming. Nevertheless it cannot be denied that the theory provides us with an intelligible explanation of a series of problems and facts which cannot be so well explained on other grounds.

On the other hand, Darwinism, i.e., the theory of Natural Selection by means of the Struggle for Existence, is being pushed to the wall all along the line. The bulk of naturalists no longer recognizes its validity, and even those who have not yet entirely discarded it, are at least forced to admit that the Darwinian explanation now possesses a very subordinate significance.

In the place of Darwinian principles, new ideas are gradually winning general acceptance, which, while they are in harmony with the principles of adaptation and use, (Lamarck) enunciated before the time of Darwin, nevertheless attribute a far-reaching importance to internal forces of development. These new conceptions necessarily involve the admission that Evolution has not been a purely mechanical process.