The Vegan paradox
Oh, I see. You're talking about humans as predators and why would they be moral towards others, especially prey, at all. Interesting question.
For one, because we're social animals. We evolved to have empathy for others. It was meant for our group, but it's a skill that we can use on non-humans as well.
For another, we actually only fairly recently in evolution started being huge predators. Pre-tools, we only occasionally caught small mammals, birds, or fish. We ate lots of vegetable matter, grubs, and termites.
Also, we have a lot of impulses given to us by evolution that seem paradoxical. The human mind is able to entertain conflicting impulses. Like to be selfish or to share. To procreate indifferently or to be monogamous. I don't think it's paradoxical, though it is the root of much good literature and story telling.