Emotions are part of the emolutionary tool kit of mammals. Mammals are, for the most part, very social animals and emotions help in the core aspects of social functioning.

For example, emotions cement social bonds, in the interest of both mating and parenting. They support intra-species competition, as when animals compete for status, resources and mates. They also offer invaluable help in responding to and communicating danger and, finally, they give us information as to how other group members are responding to ourselves and to the environment.

Core emotions are clearly evident in our household pets, our cats and dogs, which is why we grow so attached to them. Affection, aggression, fear, contentment, and excitement are all impossible to miss.

When a dog wags its tail and assumes a play position, it is hard not to respond with positive emotion. Likewise, when our pet cat rubs against us and purrs, this typically elicits a similarly content and affectionate response.

The limbic system, the seat of our emotions, has not changed as much as the frontal lobe across evolution. Our cortex is quite different from that of our mammalian cousins; our limbic sytem is not.

This is why we can make emotional attachments to animals of different species. Even though our intellectual brains are vastly different, our emotional brains are relatively similar.