Page:Popular Science Monthly Volume 66.djvu/234

230 though seen only in minute features, may always be recognized again. These varieties in time Waagen termed mutations. In 1891 Scott unearthed this distinction of Waagen's and clearly defined it as the hereditary or phylogenetic change of animals in time. Previous to this Osborn, without knowing of Waagen's statement, had discussed the same facts of the birth of new characters, describing them as 'definite variations.' Cope, it happens, did not follow this line of thought at all; but many other paleontologists did, notably Hyatt, whose peculiar style and multiplicity of terms obscured his depth of thought and extent of observation. Thus the term mutation acquired a definite significance among paleontologists.

It happened that De Vries, the eminent Dutch botanist, reading Scott's paper, mistakenly identified these new characters succeeding each other in time with those which he was observing as occurring contemporaneously in plants, and he adopted Waagen's term for the 'mutation theory,' which he has so brilliantly set forth, of the sudden production of new and stable varieties, from which nature proceeds to select those which are fit.

If paleontologists are correct in their observation, mutations may be figured graphically as an inclined plane, whereas De Vries's phenomena in plants represent a series of steps more or less extensive. Scott expressly excluded the element of discontinuity; and I believe there is no ground whatever for the assertion that the phenomena first named mutations by Waagen and independently observed by many paleontologists, are identical with the phenomena observed by De Vries in plants.

On the contrary, De Vries's facts accord with the favorite hypothesis of St. Hilaire. They demonstrate the law of saltation. This is the inevitable interpretation of the expositions of De Vries himself, of Hubrecht, and of the more recent references of Bateson in his British Association address. That saltation is a constant phenomenon in nature, a vera causa of evolution, no one can longer deny. Bateson shows that it harmonizes with Mendel's conceptions of heredity, and it may be regarded as par excellence the contribution of the experimental method.

Similarly, I regard mutation as a quite distinct phenomenon, and as par excellence the contribution of the paleontological method; it is the gradual rise of new adaptive characters neither by the selection of accidental variations nor by saltation, but by origin in an obscure and almost invisible form, followed by "direct increase and development in successive generations until a stage of actual usefulness is reached, where perhaps selection may begin to operate. While clearly setting forth the difficulties, I at one time attributed definite variation or mutation to Lamarck's principle of the inherited effects of habit as the