Human evolution theory utilizing concepts of neoteny & female sexual selection
An etiology of neuropsychological disorders such as autism and dyslexia, and the origin of left handedness.

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R. A. Fisher

The Genetical Theory of Natural Selection: bibliographical excerpts


"Certain remarkable consequences do, however, follow if some sexual preferences of this kind, determined, for example, by a plumage character, are developed in a species in which the preferences of one sex, in particular the female, have a great influence on the number of offspring left by individual males. In such cases the modification of the plumage character in the cock proceeds under two selective influences. (i) an initial advantage not due to sexual preference, which advantage may be quite inconsiderable in magnitude, and (ii) an additional advantage conferred by female preference. The intensity of preference will itself by increased by selection so long as the sons of hens exercising the preference most decidedly have any advantage over the sons of other hens, whether this be due to the first or to the second cause. The importance of this situation lies in the fact that the further development of the plumage character will still proceed, by reason of the advantage gained in sexual selection, even after it has passed the point in development at which its advantage in Natural Selection has ceased. The selective agencies other than sexual preference may be opposed to further development, and yet the further development will proceed, so long as the disadvantage is more than counterbalanced by the advantage in sexual selection. Moreover, as long as there is a net advantage in favour of further plumage development, there will also be a net advantage in favour of giving to it a more decided preference. The two characteristics affected by such a process, namely plumage development in the male, and sexual preference for such developments in female, must thus advance together, and so long as the process is unchecked by severe counterselection, will advance with ever-increasing speed. In the total absence of such checks, it is easy to see that the speed of development will be proportional to the development already attained, which will therefore increase with time exponentially, or in geometric progression. There is thus in any bionomic situation, in which sexual selection is capable of conferring a great reproductive advantage, the potentiality of a runaway process, which, however small the beginnings from which it arose, must, unless checked, produce great effects, and in the later stages with great rapidity." (Fisher, R. A. (1930) The Genetical Theory of Natural Selection. Oxford. Clarendon Press pp. 136-7)

"In species so situated that the reproductive success of one sex depends greatly upon winning the favour of the other, as appears evidently to be the case with many polygamous birds, sexual selection will itself act by increasing the intensity of the preference to which it is due, with the consequence that both the feature preferred and the intensity of preference will be augmented together with ever-increasing velocity, causing a great a rapid evolution of certain conspicuous characteristics, until the process can be arrested by the direct or indirect effects of Natural Selection." (Fisher, R. A. (1930) The Genetical Theory of Natural Selection. Oxford. Clarendon Press pp. 145)

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