How to save a life?

Can we just let everything go and hope for the best? One picks the path but never get to choose the course. Whose life is more important? Ours or theirs? Without them, we will extinct; without us, they may survive better. By now, our destruction is irreversible. We are their only hope of continuous persistence. We seem to make the same mistake over and over again, and yet only a small part of us understood our error. The rest kept doing it in greed. How to save a life?