Friendship is something often associated with the human species. Most of us make dozens of friendships in our lives and gain a great deal from them – we get love, support, even, as we now know, all sorts of health benefits from these close relationships. But scientists now believe that other animals also make friends and sometimes bonds can even occur across species – have you heard of the famous friendship between Mzee, an Aldabran tortoise, and Owen, a hippopotamus. So what are the origins of friendship in humans and animals and what purpose does it serve? Today we’ll look at what friendship is and how it evolved with University of Pennsylvania primatologists ROBERT SEYFARTH and DOROTHY CHENEY – they recently published an article on this topic in the Annual Review of Psychology. We’ll also talk to veterinarian JAMES SERPELL, director of Penn’s School of Veterinary Medicine’s Center for the Interaction of Animals and Society, who has seen strong bonds between pets and between pets and humans.