The circuitry that reinforces pro-social interactions is highly reinforcing and evolved over millennia, likely because being social was adaptive for reproductive purposes and protection against predators in primitive human and pre-human species.

“is that the circuitry that is telling us a pro social positive interaction is so highly reinforcing, evolved over millions of years, or hundreds of thousands of years, whatever that is. And the only hypothesis I can come up with, and Andrew, you may be able to come up with better ones, is what I alluded to earlier, is that it was very adaptive when we were more primitive organisms, never mind non human primates, but when we were whatever we were, to be a social species for basically primarily two reasons, for reproductive purposes, it increased your likelihood of reproducing if you were hanging out with other members of your species in a non aggressive way and for protection against predators.”