Why original human nature is social , not selfish

The first human societies had an extraordinarily high survival need to to rely on each other at levels of solidarity that we cannot even imagine.

The intensity of the network of social connections of a band of 25 to 50 people living in the ecological food chain location of very fierce predators would almost constitute a new level of organic organization and integrity above individual bodies; ancient kinship/culture systems were super-organic bodies; the human social group was a highly harmonious multi-individual Body, "organism". The Individual human bodies, all of the Some Bodies, were very frail and weak relative to the field of predators they were escaping. Up-right posture made them slower runners in escape sprints, too!

The dominance of the food chain that humans ultimately reached even in the Stone Age could be reached only by super-social, super internally-cooperative, super-intra-species harmony, because they had relatively_frail_ individual bodies, and needed each other's support. It is clear to me that natural selection picked hominin groups with policies of "love thy neighbor as thyself " and "charity" over those that might have derived principles of "selfishness and greed", if there were any in the Stone Age before Civilization. Institutionalized war would have been selected against severely . And there was no material wealth to take in "war." ( See eminent anthropologist, Marshall Sahlins "Original Affluent Society " essay ).