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Yet the truth is that men and women differ equally in this very respect. Women do not suffer from hæmophilia, but they convey it. Just as definitely as one man is hæmophilic and another is not, so one woman will convey hæmophilia and another will not. The abnormality is present in her, but it is latent; or, as we shall see the Mendelians would say, "recessive" instead of "dominant."
We are accustomed to think of Mendelism as simply a theory of heredity, by which term we should properly understand the relation between living generations. Now Mendelism is certainly this, but I believe that it is vastly more. Already the claim has been made, though not, perhaps, in adequate measure, by the Mendelians, and I am convinced that their title to it will be upheld.
The Mendelians have emphasized the rôle of the unit factor in heredity, and the conservation of the unit factor as an entity through all the adventures of matings. Also, that when unit factors, say of the color of the eyes, come into conflict, brown or black being mixed with blue or grey, one, the recessive, is submerged and overlaid but not destroyed by the other, the dominant.
Mendelians find it so difficult to conceive of the origin of a new dominant that they even suggest that no such thing ever occurs: what appears as a new character was present from the beginning, but its development was prevented by an inhibiting factor: when this goes into one cell of a division and leaves the other free, the suppressed character appears.
In the same way it may be necessary to admit that two X chromosomes result in the development of a female, and one X, or XY chromosomes result in the development of a male. But Mendelians have omitted to consider what is meant by male and female.
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.
It is the opinion of a number of psychologists that it is inherited as what the Mendelians call a recessive, that is as a trait which will be overshadowed, if there is admixture of normal mentality, but will crop up by breeding with another mental defective.
Those who are now working at these problems experimentally, actually seeing what happens in given cases, and whom we may for convenience call Mendelians after the master who gave them their method and their key, have latterly obtained results the main tenour of which must be stated here, as they indicate the lines of a portion of the succeeding argument.
The latter date is of interest, because it coincides with the re-discovery of the work of Mendel, published in 1865, to which we must afterwards more than once refer; and the work of the Mendelians during the subsequent decade very substantially modifies much of the authors' teaching upon the determination of sex, and the intimate nature of the physiological differences between the sexes.
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.
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