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Updated: May 26, 2025
He has not only studied the chromosomes in the gametes of this fly, and made Mendelian crosses with it, but has obtained numerous mutations, so that his work is a very important contribution to the mutation doctrine. Drosophila in the hands of Professor Morgan and his students and colleagues has thus become as classical a type as Oenothera in those of the botanical mutationists.
There is a tendency among Mendelians and mutationists to overestimate the importance of experiments in comparison with reasoning, either inductive or deductive. Bateson, however, has admitted that Mendelian experiments and observations on mutation have not solved the problem of adaptation.
When we compare the results reached by the mutationists with those obtained by the Mendelians we find that they tend to two different conceptions of the relation between the gametes and the organism developed from them. The effect of a change in the determinants of the gametes according to the mutationists is evident in every part of the plant.
The mutationists and Mendelians have not shown how the essential characteristics of mutations are to be reconciled with the facts of metamorphosis, or with recapitulation in development which is so often associated with metamorphosis.
According to the modern mutationists such small differences are to be called fluctuations, and have no effect on evolution at all, are not even hereditary, are not due to genetic factors in the gametes.
Mutationists and Mendelians do not seem in the least to appreciate the importance of metamorphosis or of development generally in considering the relation of the mutations or factors which they study to evolution in general, because they have not grasped the fact that there are two kinds of characters to be explained, adaptational and non-adaptational.
All the evidence accumulated by the experiments and observations of mutationists and Mendelians goes to prove that this change is of an entirely different kind from those variations which are described as mutations, or as loss or addition of genetic factors. This being the case, we have to inquire what is the explanation of the evolution of the normal metamorphosis.
He admitted the possibility of the occasional appearance of those more distinct leaps in variation on which the present school of mutationists so strongly insists; but he believed them to be less influential, in the general trend of evolution, than the slower but much more frequent variations.
It is claimed by mutationists that mutations are not new combinations or separations of Mendelian unit characters already present, but are themselves new characters, though not always necessarily, as in the case of rubricalyx, new unit characters in the Mendelian sense.
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