Page:Popular Science Monthly Volume 68.djvu/490

486 American species produced by Mr. Burbank, have been in past years sold in the cities of Germany. In any event, we have as yet no reason to assume that the various mutants of the evening primrose are in any sense comparable to the wild species of the same group now existing in America.

While saltation remains as one of the probable sources of specific difference, its actual relation to the process of species-forming in nature is yet to be proved.

Dr. de Vries's assertion that the process of natural selection is mainly a conflict between saltatory offshoots and not a competition between similar individuals ('intraspecific instead of interspecific competition') is hardly justified by the facts. The real conflict is that of the individuals maintaining life against the pressure of external conditions.

In the struggle for existence, each individual survives which can. The close presence of other similar individuals and that of unlike individuals are alike parts of the environment which each individual that leaves progeny has in some degree succeeded in conquering. This conquest takes place through adaptation to the actual conditions, concession to the actual environment.

It is highly probable that saltations in general are of the same nature as fluctuations, and that they occur in nature far more commonly than has been supposed. Unless in some way protected by isolation, the traits thus developed are likely to be swamped and lost by interbreeding with the mass. But it is conceivable that they are not always thus lost, as a very favorable variation may overwhelm the mass. But it is also clear that isolation of some sort would be usually, if not always, essential to any survival of a group possessing saltatory characters.

In crossing related species, new forms arise, having in part a blend or a mosaic of the characters of the two parent species, in part other traits or characters, the origin of which may not be clearly traced. Usually the second generation shows a great range of variation, often deviating farther in some respects from the average type than was the case with either of the original parents. The progeny of these variants may also vary widely. It has been sought to define the laws governing these variations. When only a few easily recognized characters are concerned, it has been possible to trace a certain regularity, conforming in general to the Mendelian law. But different species differ not in one way, but in a thousand ways. These traits are so interwoven and so variously related, some of them cumulative and some contradictory, that in most cases no law determining which characters shall be dominant in each case and which recessive can be made out. While the