Natural selection is the first and most powerful of the selective processes. Sexual selection, Lamarckian selection (or the adopting of acquired characteristics), and additional selective processes outlined in this work, were created by the branching evolution of the selective processes themselves. In other words, not only do species evolve, but so do the processes behind species creation - a meta evolution.
Recent discoveries in neuropsychology evocatively support a side branch of contemporary evolutionary theory, heterochronic theory, which covers the study of neoteny in human evolution. There is a powerful body of evidence that suggests that Darwin’s third theory, pangenesis, makes way for an understanding of the etiology of neurological disorders in human beings as evidenced in recent discoveries of human hormonal structures and neurological anomalies.
There is powerful evidence that it was in periods of great climactic change that our ancestors made their greatest physical and societal evolution. Humanity's origin my have risen from a period when, during a time of food scarcity, the female hominids choose males inclined toward supplying the community (including his own unknown progeny) with food. Chimp behavior can suggest how the female hominid may have gone about choosing the father of her child, for it is with the premise that the early hominid female participates in choosing her copulation partner, just as in chimpanzee society, that this theory begins to fall into place.
Briefly, we are proposing that for two million years, up to approximately 100,000 to 40,000 years ago, hominid evolution was driven by the criteria females used to select males for their procreation partners (Tanner, 1981) included males who were increasingly cooperative, social, and less aggressive (Young 1971). Males with these characteristics were more inclined to succeed in a promiscuous social environment (Morgan, 1877;Margulis & Sagan, 1991) and more likely to be responsive to the needs of women with infants and children helpless for long periods. These characteristics were evidenced by males with less testosterone (T) than the more aggressive males.
By choosing males with low T, females are prolonging the developmental and maturation rates of their male progeny. In humans the relative levels of testosterone (and probably estrogen) in males and females is the primary hormonal intermediary between the eight environmental cues and relative rates of maturation. By prolonging growth, whether explained by heterochronic concepts of neoteny (Montagu, 1955, 1989; Gould, 1977) (prolonging child features into adulthood) or by hypermorphosis (Shea, 1989; McKinney and McNamara, 1990) (prolonging all developmental stages), one of the net results is increased brain and cranium size (Riska & Archley, 1985). Prolonging growth rates is achieved in humans by lowering T. Accelerating growth, in effect condensing developmental stages, is achieved by raising T.
The bonobo are more neotenous than the chimpanzee, and humans, more neotenous than the bonobo. The influence of neoteny results in a more socialized male, an increased emphasis on sex, yet a decrease in aggression. These are behaviors associated with neotenous evolution that when reinforced by sexual selection can explain how the human species evolved, an explanation supported by patterns revealed by the neuropsychological literature.
For the first two million years of hominid evolution males and females had developed an increasingly androgenous (Hassler, 1992), promiscuous dance and song driven culture (Knight, 1991). When a fully linear language appeared, female and male evolutionary trajectories diverged. There was a further shift to an aggressive male, high T frame of reference enforced by patriarchal societal criteria in sexual selection. In this emerging polygynous culture males chose females for their low T docility and for those characteristics evidencing high fertility. Females that looked and acted young were more likely to be chosen to have progeny. Males now choose females for their neotenic features (Jones, 1995).
It is in a patriarchal context that much of the sociobiological (Chagnon & Irons, 1979; Buss, 1989) and evolutionary psychological (Barkow et. al., 1992) criteria for natural and sexual selection in humans makes sense. Patriarchal society could control the kind of male that would have the opportunity to procreate. Female infanticide is patriarchal culture's method for keeping only high T males in the procreation pool. Shift theory suggests that female infanticide, the culturally encouraged killing of female infants, is one of the manifestations of sexual selection in a cultural context. Female infanticide can now be understood as a form of cultural preservation.