By now I have reached an age at which my birthdays can be thought of as a countdown to the inescapable end. We live our life without knowing when that end will come. But acknowledging its inevitability encourages us to build monuments of our accomplishments that will outlast us. Of course, our DNA can give us that sort of longevity through our children. But we often wish to add meaning to the world we leave behind that goes beyond our genetic code.