The origin of what I'll call "social accounting" is clear. We're a predator species that survives risk by mutual sharing. When we succeed in a hunt we have more than we can consume or carry, so we share with others. When we fail, we beg. On average this exchange works out and keeps us alive. Yet it is vulnerable to freeloaders who cheat by always begging, never hunting. To beat them, we evolved tribal identity and accounting.
