So if the lion knew what he was doing, he would become a vegetarian??
Fighting over a mate has genetic advantages for the species. The lion isn't trying to be good or moral, it's just responding spontaneously to it's nature. The notion that such an animal would not behave as it does if it knew better is already the judgment of the behavior that separates humans from the rest of the animal kingdom, and it's this judgment that leads to suffering.
Whether or not judgment is inherent in human nature depends upon perspective. It is in the nature of 'self aware' creatures to experience suffering and to respond in various ways to that suffering, including violence, but this same ability allows for the possibility to also transcend that suffering, and therefore the behavior.