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Updated: June 24, 2025
Mechanical irritation, especially of the interrupted kind, repeated blows or friction causes hypertrophy of the epidermis and of superficial bone. I have stated this argument and the evidence for it in some detail in my volume on Sexual Dimorphism.
It is of primary importance to note here, that in the case of dimorphism of the sexes abrupt modifications occur in connection with unilateral heredity.
There is one point in which this sexual dimorphism in the Plaice appears to differ from typical cases, and which suggests that the greater spinulation of scales in the males has no function at all in the relations of the sexes, and is therefore not subject to and external stimulation.
His remarkable paper on Sexual Dimorphism had been translated into several languages, and a furious polemic had broken out over it. When a young fellow can get the big men fighting over him his future is pretty well assured. But Dredge was only thirty-four, and some people seemed to feel that there was a kind of deflected nepotism in Lanfear's choice.
Leaving now the description of these special cases, we may resume our theoretical discussion of the subject, and try to get a clearer insight into the analogy of ever-sporting varieties and the wild species quoted. All of them may be characterized by the general term of dimorphism. Two types are always present, though not in the same individual or in the same organ.
He considers it is quite as conceivable that selection should operate to pick out inconspicuously coloured females as that selection of brilliantly coloured males should bring about an addition to the female type. But as pointed out above, selection cannot explain the dimorphism in either case.
MacLachlan informs me of another instance of dimorphism in several species of Agrion, in which some individuals are of an orange colour, and these are invariably females.
It would take up too much space to show the various steps, through dimorphism and other means, by which the separation of the sexes in plants of various kinds is apparently now in progress; but I may add that some of the species of holly in North America are, according to Asa Gray, in an exactly intermediate condition, or, as he expresses it, are more or less dioeciously polygamous.
It is obvious from the above facts that however interesting and important sex-linked heredity may be, it is not the same thing as the heredity of secondary sexual characters, and does not in the least explain sexual dimorphism.
Shyness of adorned male birds; Siagonium, proportions of the sexes in; dimorphism in males of. Siam, proportion of male and female births in. Siamese, general beardlessness of the; notions of beauty of the; hairy family of. Sidgwick, H., on morality in hypothetical bee community; our actions not entirely directed by pain and pleasure.
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