At any rate you people cannot justify something on the basis that it exists in the animal world. Cannibalism, killing rivals, killing the male after mating, killing offspring of rivals, eating ones own offspring, mating with siblings or offspring.... are all routine part of many species in the animal world. They are however not acceptable in human society.
The very idea of spirituality (as also civilized societies) is to move away from animal tendencies.... to control and regulate our impulses.