Social capital and the human psyche: why is social life "capital"?

In this article, we propose a revised definition of social capital, premised on the principles of evolutionary psychology. We define social capital as any feature of a social relationship that, directly or indirectly, confers reproductive benefits to a participant in that relationship. This definition grounds the construct of social capital in human nature by providing a basis for inferring the underlying motivations that humans may have in common, rather than leaving the matter of what humans use capital for unspoken. Discussions and empirical reviews are presented on the innateness of human sociability, sex differences in sociability, and psychological mechanisms that mediate sociability.