Sexual Dimorphism


MR. CUNNINGHAM'S reply does not appear to me to shed any new light upon the subject of unisexual inheritance, and I can only adhere to the statement expressed in my review. Why he credits me with the supposition “that all spontaneous variations are inherited only by offspring of the same sex as the parents in which they occurred” is beyond my comprehension. There is nothing in my criticism of his views which warrants this, and I need hardly add that the facts which prove such a supposition to be erroneous are quite as familiar to me as they are to Mr. Cunningham. The real point at issue is a comparatively simple one. The author of the book insists that the theory of sexual selection fails to account for unisexual inheritance, and that his theory does account for this phenomenon. Again, it may be asked, why? The answer given above is simply a repetition of his opinion, as already published—the characters are so limited “because they were due to stimulations similarly limited.” That is to say, that in every case where the male possesses distinctive secondary sexual characters, these have been produced by direct stimulations acting on the male only, and are, therefore, limited by heredity to the male. Now Mr. Cunningham has just pointed put that transference of male characters to the female does take place, that blending of characters may, and does, occur, and that male characters may, under certain circumstances, appear in the female—a series of facts which we have all been familiar with ever since we became students of Darwin's writings. These facts are absolutely inexplicable on the “direct stimulation” theory. If the stimulations which produced a male character necessitate the restriction of that character to the male, then the only way of escaping from the dilemma in which the author has placed himself is to make one of two additional assumptions:—(1) The characters so blending are not secondary sexual characters, which would be simply resolving the question at issue into a verbal juggle; or (2) that in all cases where there is blending or transference, the same “stimulations” have acted upon both sexes. This last assumption is, however, opposed to the entire spirit of Mr. Cunningham's book, the whole burden of which is that there has been dissimilarity of “stimulation” between the sexes.


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MELDOLA, R. Sexual Dimorphism. Nature 63, 252 (1901).

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