why care about the long-term existence of our species? certainly we should strive to leave a better world for our children, their children, and their children's

why care about the long-term existence of our species? certainly we should strive to leave a better world for our children, their children, and their children's children, but past a certain point it seems very abstract to me. even 10,000 years is about three times as long as the totality of recorded history. in 100,000 years, our genome may have diverged enough that whatever humans live at that point in the future wouldn't be the same species anyway. why should I, a sentient sack of meat living in the year 2020 care about these things? more to the point: why should I sacrifice improving the lives of any currently living beings for the sake of ones that may live in future millennia?