Page:Popular Science Monthly Volume 63.djvu/23

Rh to ascribe specific rank to insular forms differing in details utterly inadequate for the diagnosis of widely distributed continental types. Multiplicity of species does not signify that the land-snails of the isolated valleys of the Hawaiian Islands are in a state of more rapid evolution than other mollusca, but that the characters of these segregated groups are so uniform that systematists can readily define and distinguish them. Many very small species are known, but they are extremely few in comparison with those of larger distribution, and with suggestive frequency they present indications of approaching extinction.

The uniformity of such narrowly segregated groups is the same as that of many of our varieties of domesticated plants and animals, the history of which is also brief. We have, moreover, with these the opportunity of observing the further symptoms of the process of decline.

As though to compensate for the want of access to the normal number of variations, those which occur become more and more striking, and may even be more different from the parent form than the wild species of the same genus are from each other. They have been said, in other words, to 'answer the definition of species.' Professor De Vries has courageously accepted the results of this reasoning and has equipped his new Oenotheras with specific names and introduced them to the scientific world as new members of the vegetable kingdom in regular standing, while the description of many other 'De Vriesian species' is threatened by some of our too-progressive naturalists.

The inadequacy of natural or other forms of selection as an explanation of evolution has become more and more appreciated, and has decreased confidence in the Darwinian idea that species originate by imperceptible gradations, impelled by natural selection. Professor De Vries and his followers argue accordingly that species must originate by definite and abrupt changes, and have set out to search the biological field for instances to support this theory. But if the present interpretation of evolutionary facts and factors be correct the forms described as 'mutations' are not true evolutionary species, either actual or potential. Mutations more fertile than the parent type have not been reported. They do not arise through normal evolution, but are symptoms of debility due to the absence of evolutionary opportunities; they are not parts of an ascending series, but are obviously declining toward extinction. This difference of interpretation well shows the antithesis of static