Can "That I die" change the essence of human nature?

To be alive is already to be dead, is the only way we can be dead.
To die the prerequisite is that we are or have been alive.

Notice the similarities in To die and Tode (German) and in Mortality and Mortalite (French). Death is one and perhaps the only "idea" that translates perfectly from person to person even over different languages. We all realize we will die. I will die. Perhaps we understand death differently according to our culture and education (we can even want it, according to our genetics), but the tragic or blissful thought THAT I will die is universally acknowledged and has to form the basis of a community that peacefully shares in a mutual wanting to avoid our deaths. But the fear of the anxiety that the thinking of death causes causes us to avoid thinking this basis, thinking this commonality that unites. Without this thinking we cannot share, and we certainly cannot give without expecting or desiring return, something that this thinking can give way to as a general feeling in the worldspirit.

But the question of human nature comes down to one thought:

We are by nature selfish, that is, all actions are essentially and ultimately selfish actions, unless it can be said that SOME humans will TRY to do good and benficial things for others that have no gain for themselves, and fail, and keep trying, endlessly, never giving up. For they cannot even gain the satisfaction with themselves of having done these things for others without having similar good things done in return. Is this possible? I don't think so, but we will never know.