PUBLIC RELEASE: 22-JAN-2018
Researchers report potential explanations for the evolution of social behavior and intelligence in humans. Humans are characterized by remarkable demographic success compared with our nearest relatives and by advanced social traits such as language, empathy, and altruism. Explaining how human social behavior could have evolved by improving individual reproductive success has been challenging. Owen Lovejoy and colleagues compared neurochemical profiles in the striatum, a brain region that modulates social behavior, among humans, chimpanzees, gorillas, baboons, and monkeys. Humans and great apes had elevated levels of serotonin and neuropeptide Y, compared with other primates. However, striatal dopamine levels were higher and acetylcholine levels were lower in humans than in gorillas or chimpanzees. The human neurochemical profile is consistent with enhanced sensitivity to social cues, social conformity, and reduced within-group aggression. Such a dopamine-dominated striatum (DDS) personality style could have encouraged male provisioning and monogamy in early hominids, which would have improved female and offspring survival. The authors further suggest that reproductive success conferred by the DDS personality would have led to selection for increased social awareness and advanced social behavior, and ultimately to increased brain size and language. In a related study, Lovejoy and colleagues examined the mortality and fertility of macaques, the most demographically successful primates after humans. The authors determined that a key to macaques' reproductive success was elevated female survivorship. According to the authors, a socially monogamous lifestyle would have increased female life expectancy in early and later hominids.
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