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Updated: May 16, 2025
The majority of evolutionists in recent years have taught that influences exerted through the soma have no effect on the determinants in the chromosomes of the gametes, that all hereditary variations are gametogenic and none somatogenic.
How far Doncaster is right in holding that the soma is different in the two sexes is a question already mentioned, but it is obvious that in each individual the somatic sexual characters proper to its species are present potentially in its constitution by heredity in other words, as factors or determinants in the chromosomes of the zygote from which it was developed; but the normal development of such characters in the individual soma is either entirely dependent on the stimulus of the hormone of the gonad or is profoundly influenced by the presence or absence of that stimulus.
It might be agreed that if the determinants are stimulated or deprived of stimulation, the effect of the change should logically show itself from the beginning of development, and that therefore the process of metamorphosis or indirect development does not support the hormone theory any more than the theory of gametogenic mutations. This objection may be answered in the following way.
Weismann saw no possibility of changes induced by any sort of stimulation in the soma affecting the gametes in such a way as to be redeveloped in the soma of the next generation. He attributed variation partly to the union of gametes containing various determinants, which he termed amphimixis: this, however, would introduce nothing new.
The analysis is certain to be unconscious, or rather unknown, to the normal speaker. How, then, can we be certain in such an analysis as we have undertaken that all of the assigned determinants are really operative and not merely some one of them? Certainly they are not equally powerful in all cases. Their values are variable, rising and falling according to the individual and the locution.
A system which is part of a deterministic system I shall call "determined"; one which is not part of any such system I shall call "capricious." It is to be observed that a system which has one set of determinants will in general have many. In the case of the motions of the planets, for example, the configurations of the solar system at any two given times will be determinants.
Theory supposes that somatic modifications by means of hormones affect the determinants in the gametes. But it is obvious that the black and white of Leghorn fowls and of guinea-pigs are gametogenic characters, and are strongly established in the gametes of their respective varieties.
The main determinants for the woman's preference for the neuroses, especially for hysteria, lie in this change of the leading zone as well as in the repression of puberty. These determinants are therefore most intimately connected with the nature of femininity.
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.
We may suppose, therefore, that the determinants of the zygote have acquired a tendency to produce the increases and decreases of tissue which constitute a certain modification, e.g. the change in the position of the eyes in a Flat-fish, but the stimulus which caused this tendency has always acted when the adult combination of hormones was present.
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