- Cannibalism, where animals of the same species do indeed eat one another. Chimpanzees sometimes eat one another, as do some forms of snakes, insects and other animals.
- Sexual Cannibalism, where the female eats the male either before, during or after they engage in sex. This is most commonly seen in some types of spiders, scorpions, and most famously praying mantises.
- Filial Cannibalism, perhaps the most infamous form of cannibalism in the animal kingdom, is where one of the parents or both eat the young. Most people attribute this to hamsters and gerbils, but it can also be seen in some species of apes, pigs, rabbits, fishes and insects.
- Infanticide, where an animal may intentionally kill (not necessarily eat) either their own young or the young of other broods. This can be seen in many types of rodents, large cat breeds, birds, fish and others.
- Polygamy, where a male has various female partners in simultaneous relationships. An alpha male lion may live with and impregnate an entire tribe of lionesses, and some prairie dog males will live with four or more females in a tight community. This behavior is also seen in many forms of horses, fishes, mice and apes.
Should humans practice all of these simply because they are found in the animal kingdom? Should humans be all right with others practicing these things simply because animals do them as well?