The idea that if we help each other when we are in a position to. (Low cost for us. High cost for other).
Also don't cost others suffering.
How you look at it. Are we being selfish or selfless is up to your personal preference of optimism / skepticism. It doesn't really matter.
Ideally if you believe in a type of consciousness rebirth - Likely not taking anything from past life but as we were never dead our consciousness probably* mutates to being a different person.(Do you really think you "Are" the person you were at birth?) -
Then you will want to have enlightened self interest. Personally I believe causing others suffering (Eating animals ect) is a kind of cannibalism / self inflicting harm.
Why is it that we think of ourselves as OTHER?
Survival is at our core but otherwise it is foolish not to work together.
I'm afraid society is moving towards a kind of semen race to the top. Mindless acquisition of material goods to satisfy the ego. We can do better.