“No one, least of all Williams and Kafatos, expect the eventual story to be so simple. But it does seem likely that normal development is controlled by gradually decreasing concentration of a hormone acting primarily at high levels of the regulatory system. This is also an ideal mechanism for the simple and rapid production of heterochronic effects. Any acceleration of adult characters by reduction in the titer of juvenile hormone, or extension of juvenile traits by maintenance of a high titer, represents heterochrony. Since minor alterations in the concentration of a hormone can lead to substantial changes in morphology, heterochrony may play an important role in geographic variation (secretion of juvenile hormone is influenced by temperature and photoperiod, for example), polymorphism (including sex, caste, and phase) and speciation itself.” (Gould, S.J. (1977) Ontogeny and Phylogeny. Cambridge: Belknap Press, pp. 295-6)

A premise of this work, this theory I’m calling the Theory of Waves, is that testosterone is instrumental in changing rates of maturation, leading to neoteny and acceleration. I’ve been eating and breathing this assumption for so long I forget that it is little discussed in the biological literature, let alone in neuropsychological or anthropological discussions. Gould above alludes to it, but I can’t find anywhere else in his papers or books that he goes into detail discussing the hormonal foundation for heterochrony. Darwin’s last great work, The Variation of Animals and Plants Under Domestication, proposed a theory that described the sexual organs as producers of a substance that was influenced by the environment to impact evolution in a single generation. Darwin called them gemmules. We’d call them testosterone, estrogen and related hormones.

Gould seemed loath to explore in public Lamarckian implications of heterochronic theory. He described his colleagues’ confused responses to his having heavily emphasized heterochrony and recapitulation in his 1970s work, Ontogeny and Phylogeny. A focus on nineteenth century and early twentieth century non-natural selection evolutionary theory was not looked at as a conventional research path. Gould walked that path carefully. He was rewarded with deep positive regard and a host of graduate theses building off his work. Still, only recently has mentioning Lamarck’s name become a respected act, in large part because of the recent influence of evolutionary developmental biology.

Of the many assumptions built into this subtle and complex Theory of Waves, perhaps this is the most instrumental. Testosterone levels and the timing of testosterone’s introduction determine heterochronic trajectories, including maturational delay (paedomorphosis and neoteny) and maturational acceleration (recapitulation and condensation).

This work has taken a step further, hypothesizing that estrogen levels and the timing of estrogen introduction determine sexual selection proclivities (the focus on particular features as desirable) in addition to an attraction to childlike features. I can’t say I’ve consciously come across this suggestion in the literature. I’m pretty sure it’s there, probably in non-obvious contexts. Googling “estrogen” and “sexual selection” brings up this site first, suggesting there is little competition for the concept. My site receives no visitors searching for that term.

I’ve wracked my brain for many years, wondering why there is so little attention to the relationship between the sex hormones and human evolution. There are researchers out there, like the late Ryuichi Matsuda (see http://www.serpentfd.org/a/matsuda1987.html) with intuitions for these issues. It seems his work is not mainstream, or if mainstream, it seems he’s little followed, though I note he’s getting some attention from evolutionary developmental biologists. This is good.


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