To humans, it is built in. We are social animals, we have a strong tendency to collect together in groups, thus we develop these basic rules of thumb that allow us to on the very basic of levels, maximise the benefit of being in a group.

Lions, for example, are different in thier social makeup. A male lion will preside over multiple females, and selfishly guard them against any potential rivals. A lion that challenges and kills another lion that leads a pride will tend to commit infanticide, and kill all cubs so that his genes are definetely going to be passed on.

However, many species of birds will have multiple partners, and will collect thier young with other young in the community, and practice more altruistic behaviors towards each other, one being taking care of and protecting other birds' young.

Even animals behave intrinsically in very different ways, due to that way that they have evolved to interact with each other.