Concerning the Mutation Theory

Abstract

The mutation theory of evolution has met with a stormy reception, despite the fact that De Vries, and most of its supporters, have avowed themselves adherents of the doctrine of natural selection. Some of the older followers of Darwin have insisted that the large steps, which they still believe are the only kind that the mutation theory postulates, could not give the small continuous stages through which evolutionary changes take place. Now, the mutation theory has never made any such "large" claims. On the contrary, it has been pointed out repeatedly that the mutational changes may, be extremely small. The theory does claim that the genetic factors are discontinuous, although the characters that they stand for may or may not be discontinuous. De Vries himself has said in the "Mutation Theory" (Vol I, page 55): "Many mutations are smaller than the differences between extreme variants," meaning by the latter term fluctuating variations, pointing out by way of illustration that the constant species of Draba verna " differ less from each other than do extreme variations in the same characters." While De Vries's work on the evening primrose, (Enothera Lamarekiana, is generally conceded to be the starting point of the modern mutation theory, nevertheless, the peculiar way in which Lamarck's primrose produces its new and recurrent types, which De Vries regarded as the real mutative process, has been difficult to harmonize with the way in which practically all other forms give rise to mutants.