Why do people believe in an afterlife?

Is there some gene or something? I know this is kind of hard to understand, but i really feel like believing in an afterlife is irrational, and i want to stop believing, but the belief is there, and i hate it! I can't fix my mind to think there are no spirits or god or afterlife or whatever! And I don't know how to explain it either. It's like i feel like im delusioned or something. I know it's irrational, but i find myself thinking and believing in it a lot. So, is this some sort of heredity thing or something?