Did Homo sapiens self-domesticate?
“Self-domestication” here refers to the evolution of a reduced propensity for reactive aggression (compared to an immediate ancestor), without the active involvement of another species. Animal species that have been domesticated by humans all have low reactive aggression and also tend to share a suite of behavioral, physiological and anatomical symptoms (the “Domestication Syndrome”). This suggests that in self-domesticated species a parallel set of features should be found (the “Self-Domestication Syndrome, SDS”), which I illustrate with evidence for bonobos compared to chimpanzees. In humans, evidence of self-domestication comes from a low propensity for reactive aggression and an anatomy indicative of a SDS. I show that the communal sanctions practiced by hunter-gatherers, which depend on proactive aggression, provide a leading candidate mechanism selecting against high levels of reactive aggression. I therefore propose that human self-domestication is an ironic consequence of a particularly well-developed facility for proactive aggression. I conclude that humans indeed self-domesticated, providing a critical underpinning for inter-individual tolerance and cooperation.