Thursday, March 8, 2018

Evaluating the self-domestication hypothesis of human evolution

Marcelo R. Sánchez-Villagra and Carel P. Van Schaik
AAPA 2018, Meeting Program Abstracts
April 11-14, 2018
Early XXth century studies posited how the very traits that are so variable in humans are precisely those recorded as highly variable among domesticated species subject of intense selective breeding, as in dog breeds. The current version of the self-domestication hypothesis posits that the effects of selection against aggression in morphology, physiology, behavior and psychology reported for domestic animals operated in human evolution too. This hypothesis attempts to explain the behavioral and morphological changes in human evolution from the Middle Pleistocene to recent times, in particular, our reduced aggressiveness and the shortening of the upper facial skeleton and a reduction in brow ridge projection: these changes are tied to physiological changes connected to the rise of high levels of social tolerance and its cognitive consequences.

Unfortunately, the self-domestication hypothesis cannot easily be reconciled with the complex and multivariate empirical record of morphological features of humans. Its full evaluation requires (1) data on rate and variation in human evolution (currently lacking); (2) specification of the time window (if the Holocene is included, the confounding effects of agriculture and sedentary life must be removed); (3) a complete test of the neural crest mechanisms that would be associated with the coupling of traits in domestication (hardly testable for mammals, and although testable in chickens using developmental genetics tools, this model may not be applicable to a primate, because clades of tetrapods vary in the relation between neural crest development and adult morphology).

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