Imagine that your life began as one of the planet’s first humans. After dying, you're reincarnated as the second human ever to live. You then return as the third person, the fourth, the fifth, and so on – living the lives of every human that’s ever walked the Earth. How will your actions in one life impact your future selves?  Examine the ethical stance known as longtermism, which is the idea that we should be doing more to protect future generations.