"What we ought to do depends on what is. The is of nature differs significantly from the is of culture, even when similar suffering is present. A human being in a frozen river would be rescued at once; a human attacked by a wolverine would be flown by helicopter to the hospital. Bison and deer are not humans and we cannot give them identical treatment; still, if suffering is a bad thing for humans, who seek to eliminate it, why is suffering not also a bad thing for bison? We cannot give medical treatment to all wild animals; we should not interrupt a predator killing its prey. But when we happen upon an opportunity to rescue an animal with the pull of a rope, or mercy-kill it lest it suffer, why not? If we can treat a herd of blinded sheep, why not? If we can feed the deer, starving in the winter, why not? That seems to be what human nature urges, and why not let human nature take its course? That seems to be what Jesus urges, doing to others as you would have them do to you, and why not follow the golden rule?"