Assertion: reciprocal altruism | /r/HasProperty | primary factor
Facets:
value: certainly
type: MANNER
Source sentences:
text: This is intuitively true and explains a good deal about the way we live; though living in groups is not the only ESS (many animals lead very solitary lives except during mating season), it is the one the human race has chosen, and reciprocal altruism must certainly be the primary factor.