I would disagree with the idea that survival of oneself and their genetic offspring is the only thing people care about. It’s a very Hobbesian view, and it can be very limiting to base decisions of morality on this very narrow, static view of human nature.
The most moral decision is to pull the switch, but only if you would also want that decision to be made if you were the person on the second tracks.
Since I don’t think I would want this, I would choose to not pull the lever, as I feel I do not have the right to choose death for someone else if I lack the courage to choose it for myself. So, for myself, as a human that is not completely self-less, not pulling the lever is the most ethical choice I can make.