Cohesive kin-like groups based on mutual trust emerge without a designer

Evidence

This is a teleological or ‘functional’ argument, of course, open to the objection that the need for the cohesion of social groups will not automatically engender that cohesion. In the absence of a designer and creator, the favourite logical substitutes are our old friends, natural selection and rational foresight. Presumably each of them operates, though no one really knows in what proportion. All one does know is that a system corresponding to this model — a system of mutually supportive or, in the language of the present discussion, of mutually trusting ‘kinsmen’ — is conspicuously present, or was traditionally present. The ‘kinsmen’ need not literally be such, of course, but they do tend to be cohesive, which is a shorthand way of saying that, on the whole, they trust each other. — Diego Gambetta, Trust - Making and Breaking Cooperative…, 1935