Rethinking my oblique dismissal of "hard wiring," I apologize. I was thinking of Man, the biological system, not Man as a part of another system, a culture.

I think the Undercover Economist's hunch is correct. Civil societies, as contrasted with pre-agricultural (primitive) societies, are hard-wired for wealth inequality because they are based on property relations and not kinship relations. As Lewis Henry Morgan famously observed in the 18th century (famous at least among students of anthropology), "You do not find wealth at one end of an [American] Indian village and poverty at the other."