Humans are destined to merely be fertilizer for the planet. For some reason we live for some time in a self-aware state (between infant-hood and senility, at least) while our bodies grow and age, becoming a self contained package in an ideal fertilizer state. Yes, once we are fertilizing, there are others going through that process that we call life and there will, unless we kill the planet, be others to come in the future. Thus we toil to create and work to build a legacy to leave behind for these future fertilizers. Isn't that nice of us?