New advances in the psychology of mammals lend credence to the claim that animals feel emotion, which for a long time was supported only by anecdotal evidence. They represent a new scientific perspective on animals: rather than observing their behavior as solely the consequence of environmental, biochemical and evolutionarily advantageous factors, we are also now perceiving them as capable of experiencing the same basic experiences as human beings do.
Jaak Panksepp, a professor of psychology at Bowling Green State University and head of neuroscience research at Northwestern University, has taken maps of the brains of many mammals - humans, dogs, rats, etc. - as well as birds. In doing so, he has discovered seven emotional paths that are common throughout all these species: SEEKING, RAGE, LUST, CARE, PANIC/GRIEF, and PLAY. (In every paper he's submitted, he's written these emotions in all capital letters to indicate their importance and universality.) Not only are they experienced similarly, but they are also expressed in many of the same ways. Animals in a state of panic or grief suffer profound depression, whereas animals at play form strong friendship bonds that can span across species - though anyone who's ever owned and loved a dog, a cat or a rat could've told you that already!
Panksepp has even isolated what he believes to be a rodent's 'laughter,' chirped at a high enough range that humans have - until recently - never been able to hear it. This 'laughter' generates the same rush of pleasure-inducing hormones in a rat's biochemistry that it does ours and paves the way for rat-human friendships when it is generated through playful tickling. The effects couldn't be replicated with a machine, so we know it isn't a purely physical response; the rats only giggle and bond when engaged by another living creature in play.
So remember this the next time you're dealing with another animal, be they a pet, at a zoo, or in the wild: we have more in common with them than previously thought. Our experience of this world through emotion and social bonds is felt similarly in every mammal and bird on earth.