Human prosociality toward nonkin is ubiquitous and almost unique in the animal kingdom. It remains poorly understood, although a proliferation of theories has arisen to explain it. We present evidence from survey data and laboratory treatment of experimental subjects that is consistent with a set of theories based on group-level selection of cultural norms favoring prosociality. In particular, increases in competition increase trust levels of individuals who (i) work in firms facing more competition, (ii) live in states where competition increases, (iii) move to more competitive industries, and (iv) are placed into groups facing higher competition in a laboratory experiment. The findings provide support for cultural group selection as a contributor to human prosociality.
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