34 Broad St
Oxford, NC 27565
USA
Human self-sacrifical decisions to cooperate with others are more frequent, and they emerge more automatically, when beneficiaries belong to one’s in-group, rather than to a more or less rivaling out-group. Using quantitative techniques that covered forty years of experimental work in social psychology, sociology, and experimental and behavioral economics, we found this in-group bias to be robust and universal. Subsequent experiments reveal this in-group bias to be (i) motivated by a desire to benefit the in-group and its members, rather than to hurt or derogate competing outgroups, (ii) stronger when cooperation protects the in-group against enemies, rather than facilitates subordination of rivaling out-groups, (iii) regulated by sub-cortical brain circuitries involved in emotion-regulation and heuristic decision-making more than by prefrontal networks implicated in controlled and calculated choice, and (iv) enhanced under increased availability of oxytocin, a hypothalamic neuropeptide involved in pair-bond formation, parent-offspring interactions, and maternal defense. Findings together resonate with the idea that humans are biologically prepared for in-group bounded cooperation, and that such in-group bias is motivated more by group survival and protection needs, than by opportunities for group prosperity and expansion.