I was about to type that maybe it's about intention, but then I realised that expectation of feeling good is a reward based motivation.

Having behaviours that benefit your group rewarded and reinforced seems an obvious survival trait. It feels good, like reproduction. I wonder it's purely societal evolution or if there's a genetic component there.

Maybe it's hard to reconcile all this because calling something altruism is subjective, since we are not all knowing.