What is the difference between people who do not yet exist (future generations) and people we do not know? Can we harm the non-existent? Example: If we eat a lot of tuna now, there may not be enough tuna restocked by nature for others who follow us. So does our current hunger justify using up all the tuna? Or if others would like tuna, or will be hungry, is it our human responsibility to save some of the tuna for them? Do we owe first to those who we do not know or those with us?