The first comprehensive review of social behavior between different species gives insights into the evolutionary roots of pet-keeping.

'Heterospecific social behavior in primates: insights into the evolutionary roots of pet-keeping', published in Primates, is believed to be the first comprehensive review of friendly interactions between non-human primates and other species.

When animals of different species spend time together, it is usually for practical reasons, such as easier foraging or safety in numbers. However, this review documents 427 cases involving 88 primate species and 127 partner species, 55 of them non-primates, and finds that monkeys and apes frequently play, groom, hold, carry and even adopt individuals from other species, although not all encounters ended well.

Lead author, our Tutorial Fellow, and Associate Professor at, School of Anthropology and Museum Ethnography, Cyril Grueter, said:

'Humans have long been considered unique in forming close social relationships with other species. Our study shows that many primates also display remarkable curiosity, tolerance and even caregiving towards animals that are not their own species. These behaviours don't amount to pet-keeping as we know it, but they may represent some of the evolutionary building blocks from which human-animal companionship eventually emerged.'

Beyond shedding light on the origins of human-animal relationships, the authors believe the findings also have implications for conservation and animal welfare.

Dr Grueter said: 'Understanding why some species readily form positive relationships with others could help improve the management of mixed-species groups in zoos and sanctuaries. More broadly, these findings provide new insights into the evolution of empathy, social flexibility and the remarkable capacity of primates to engage with animals beyond their own species.'

The authors hope their review will encourage primatologists to record these often-overlooked interactions more systematically during long-term field studies.

Find out more about how monkey friendships with dogs, deer, and pigs offer clues to the evolutionary origins of pet-keeping.