I dont think we should compare humans to animals and say that just because it occurs in the animal kingdom it means its natural for humans as well. Arent there animals that eat their own feces? Arent there animals that eat their own babies? They are animals, we are humans, there is a difference. Doesnt mean that whatever animals do is automatically natural for us too
We are homo sapiens, a subspecies of the kingdom animalia. We ARE animals.
Some animals eat their babies, often due to stress and anxiety. Some humans kill their children for the same reasons, though in some cultures they may not eat them, in others they do. There are reasons species do what they do, and for human beings (as well as several other animals), sex and bonding does not exist solely between male and female. Contrary to popular belief, the sole reason for bonding is not always reproduction. When scientists have found that genetics may likely play a role in homosexuality, it's time to wake up and realize that it's in our blood.