Several years ago, I attended a seminar on the foundations of ethical systems. The participants quoted Plato, Jesus, Heidegger, and a host of other authorities; they trotted out every philosophical and theological reason why we can or should be good. Of course, prominent among the arguments was that old canard: Without the promise of eternal salvation or the threat of damnation, we would all be scoundrels.
No one mentioned that we are first of all biological creatures with an evolutionary history, and that altruism, aggression, fidelity, promiscuity, nurturing and violence might be part of our animal natures.
I looked around the auditorium and saw folks of every religious and philosophical persuasion, and of many cultural and ethnic backgrounds, and I thought, "Gee, I'd trust any one of these folks not to take my wallet in a dark alley." Sure, humans are capable of great evil, but most of us are pretty good most of the time, and I suspect that it has more to do with where we have been as a biological species than with where we hope to be going in some airy-fairy afterlife.
We are animals who have evolved the capacity to cherish our fellow humans and to resist for the common good our innate tendencies to aggression and selfishness, not because we have been plucked out of our animal selves by some sky hook from above, but because we have been nudged into reflective consciousness by evolution. When it comes to living in a civilized way on a crowded planet, I choose to put my faith in the long leash of the genes rather than fear of hellfire or the chance to walk on streets of gold.