Origin of hominids' reproductive success


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.


Article #17-19666: "A neurochemical hypothesis for the origin of hominids,"
by Mary Ann Raghanti et al.

Article #17-19669: "Early hominids may have been weed species," by Richard
S. Meindl, Morgan E. Chaney, and C. Owen Lovejoy.




Mandi Smallhorne

Freelance science journalist and writer