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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Nancy Tanner

On Becoming Human: Bibliographical Excerpts

"The more intelligent transitional female (remember, it is her offspring who will be most likely to survive) could use her intelligence to select males for copulation. In other words, increases in intelligence and a richer, more sophisticated communicatory repertoire mean the mating system itself could become more complex. I hypothesize that the mating system was changing so as regularly to include female discrimination and choice of sex partners in terms of a number of characteristics. Females probably had sex more frequently with those males who were around often, playing with offspring, helping in protection, occasionally sharing meat and foraged plants, and who were generally friendly. With females choosing the less disruptive males, there also would be less likelihood that males having sex with mothers might accidentally injure offspring. To the extent that the ability to learn to be more sociable has been enhanced by genetic changes that have augmented our human potential --- and this is a subject about which little is known --- sexual selection in the hominid divergence also could have increased the capacity of males for relaxed social interaction. ... What may have been selected for among the transitional hominid males was the capacity to be extremely social but yet sufficiently aggressive when required and an ability to make fine discriminations as to situational necessity. Thus, the males of the transitional population would come to more closely resemble the females than had the males of the ancestral population. ... Much of the selection pressure engendered by female choice of sexual partners was directed toward male social and communicatory behavior, reinforcing the potential and capacity for sociability, social learning, and intelligence." (Tanner, Nancy M. (1981) On Becoming Human: Cambridge University Press, Cambridge p. 164-5)

"He [Darwin] was prevented from harvesting all the fruits of his fertile imagination because he did not follow through with the logic of this own argument - to discover how female choice influenced the origin of the hominids; that is, to show how sexual selection was important at the very onset of human evolution. Because of an unfortunate blind spot engendered by his own cultural background, Darwin was unable to explicate the necessary interrelationships and carry his own work on to its more logical conclusion." (Tanner, Nancy M. (1981) On Becoming Human: Cambridge University Press, Cambridge p. 167)

"The evidence is also clear regarding female chimpanzees' significantly more frequent preparation and use of tools in food getting (albeit, in the case of chimpanzees, for insect gathering). Male chimpanzees simply do not use tools as often to obtain food, a fact consistent with the lesser nutritional stress on males. Further, there is not question but what mother chimpanzees share food with offspring. That tool-using, plant-gathering early hominid mothers would do likewise is probable. Also of interest are data on sexual dimorphism. Several remains at Laetoli and Hadar exhibit notable size differences---for example, the footprints at Laetoli and the upper jaws of AL200 and AL199 at Hadar. The differences in size can be interpreted as due to sexual dimorphism (Johanson and White, 1979). These size differences appear greater than those between sexes for humans today. However, the canine teeth do not appear to exhibit as pronounced dimorphism as among most living primates (Johanson and White, 1979). Quite possibly, then, A. afarensis had already undergone some reduction of sexual dimorphism, and its descendants were to undergo even more. This is consistent with the selective process hypothesized in Chapter 7: The gathering innovation led to increased maternal investment, which, in turn, was associated with preferential female sexual selection of males who, among other things, appeared less physically frightening or threatening to the females." (Tanner, Nancy M. (1981) On Becoming Human: Cambridge University Press, Cambridge p. 190)



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