That meshes nicely with the video I posted.Asked this question of another group I'm in and got a great Darwinian response.
Evolution. Our ethics are an evolved behavior same as a dog circling its bed. We just think they're special because our intelligence gives us hubris.
Those of us with an empathy behavior apparently succeeded as social creatures much better than those without. We bred more, so there are more of us, so we win. That empathy behavior forms the basis of the one near-universal ethical principle: do unto others as you would have them do unto you.
Our biological drive for survival forms the basis of our other, corollary ethical principle: do unto others before they do unto you.