Mutationism
Though later associated with Mendelian genetics, mutationism began in the 1890s (prior to the rediscovery of Mendel’s laws) with the studies of Hugo De Vries and William Bateson on naturally occurring discontinuous variations; their thoughts concerning the role of discontinuity in evolution drew on earlier ideas of William Keith Brooks, Francis Galton, and Thomas Henry Huxley.
The "mutationist" view began by abandoning Darwin's idea of automatic fluctuation, embracing instead the concept that variation emerges by rare events of mutations. This view was expressed in the writings of key founders of genetics, including Thomas Hunt Morgan, Reginald Punnett, Wilhelm Johannsen, Hugo de Vries, William Bateson and others. Assuming that heritable variation cannot be taken for granted, the mutationists saw evolution as a two-step process of the chance occurrence of a mutation, followed by its persistence or elimination (selection). The mutationists denied that selection is creative, and they gave mutation a certain measure of control over the course of evolution.
A common misconception is that the mutationists denied selection. Instead, mutationists such as Morgan simply understood its role differently. In the following passage, Morgan (writing in 1916 ) displays a clear understanding of the concept of the probability of fixation of a new mutation, which might be deleterious, neutral, or advantageous:
"If through a mutation a character appears that is neither advantageous nor disadvantageous, but indifferent, the chance that it may become established in the race is extremely small, although by good luck such a thing may occur rarely. It makes no difference whether the character in question is a dominant or a recessive one, the chance of its becoming established is exactly the same. If through a mutation a character appears that has an injurious effect, however slight this may be, it has practically no chance of becoming established. If through a mutation a character appears that has a beneficial influence on the individual, the chance that the individual will survive is increased, not only for itself, but for all of its descendants that come to inherit this character. It is this increase in the number of individuals possessing a particular character, that might have an influence on the course of evolution."
Morgan resisted calling this process "Natural Selection" because it differed so much from Darwin's view.
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