Altruism is just a romantic notion. Speaking about its existence is like speaking about the existence of a soul. Souls may well exist, but it doesn't manifest in this universe.
Everything we do is for selfish reasons and that's good actually, as it means we have real motivation to help others.
Define selfish.
Some people deliberately die to save others.
Where is the selfish part in that behaviour?
Awesome. If everybody takes care of themselves, then everybody is taken care of.