[PepeGomez]

That's nonsense, individuals don't keep their species (or often even completely different species) alive unselfishly against their own interests. Such phenotypes would soon disappear if it was so. Altruism evolved because it's good for the individual's survival.

When you try to harm something or somebody for your own benefit, there are two possibilities:

Either such behavior is common enough and the target has a defense mechanism against it and in that case you will fail and you may even get hurt.

Or, it has never been too common and in that case you may succeed temporarily. However, the fact that the weakness is being exploited creates a pressure on the potential targets to find ways, or even evolve, to get rid of it. You may succesfully exploit it, but your descendants will find it harder and harder to live that way, and they may even die out.

On the other hand, when an individual is beneficial to other idividuals, it encourages them to support it, or over time even evolve traits that will allow them to better keep those of its kind alive and it will be easier and easier over time for it and its descendants to survive and have offspring of their own.

It's basically the real life equivalent of karma. Altruism evolved because individuals and species breed each other to be good.