The Evolutionary Modification of Genetic Phenomena

The title chosen for our discussion is "Contributions of genetics to the theory of evolution," and that these contributions are of two kinds, somewhat sharply contrasted, is well illustrated by comparing HALDANE'S subject, "Can evolution be explained in terms of present known genetical causes ?" with the heading under which I chose to speak, "The evolutionary modification of genetic phenomena." My own address might equally well have been entitled, "Can genetical phenomena be explained in terms of known evolutionary causes ?" The one approach, as you perceive, is analytic and deductive. Genetic studies are regarded as revealing the mechanism connecting cause and effect, from a knowledge of which the workings of the machine can be deduced and the course of evolutionary change inferred. The other approach is inductive and statistical; genetics supplies the facts as to living things as they now are, facts which, like the living things in which they occur, have an evolutionary history and may be capable of an evolutionary explanation, facts which are not immutable laws of the workings of things but which might have been different had evolutionary history taken a different course. I can only discuss a small portion of the subject. Genetic phenomena concerning the chromosomal organization, such as the male haploidy of the social hymenoptera, as SNELL has suggested in an illuminating paper recently published in the American Naturalist, may have an adaptive significance; and I think we may look forward with confidence, as the facts become better and more systematically known, to discovering the significance of such phenomena as male linkage in Drosophila, and of the marvelously intricate chromosomal mechanism which is being unraveled by METZ in Sciara. The only two phenomena I can attempt to touch upon are those of dominance and linkage; and on these I can only put before you a selection of the facts (many of which I owe to the kindness during the last few days of other members of this congress) which seem to me to supply a good deal of light and guidance in forming an interpretation of the general body of genetic facts. As I am a mathematician by trade perhaps I should explain that I shall use no mathematics, partly because I recognize that the first duty of a mathematician, rather like that of a lion tamer, is to keep his mathematics in their place, but chiefly because I think that mathematics, though well fitted to elucidate detailed points of special intricacy, are after all only a special means of carrying out reasoning processes common to all scientific work,