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  • Researchers compiled 427 documented instances of primates interacting with 127 non-primate species, ranging from gentle grooming to violent handling.
  • The study suggests that behaviors such as curiosity and tolerance toward other species have deep evolutionary roots predating human domestication practices.
  • Experts caution that while these interactions are common, they are often ephemeral and distinct from the durable caretaking bonds characteristic of modern pet ownership.

A new scientific review challenges the assumption that keeping animals as companions is a uniquely human trait by documenting widespread cross-species interactions among primates. Researchers led by Cyril Grueter, an evolutionary biologist at the University of Oxford, analyzed data from scientific literature, media reports, and surveys of experts to identify cases where monkeys and apes engaged closely with other animal species. The resulting dataset includes 427 specific incidents involving 88 different primate species and 127 other types of animals, including mice, deer, dogs, and even pangolins.

The interactions varied significantly in nature and intensity. Many involved gentle behaviors such as grooming, playing, or carrying the other animal. For example, observations included a female gibbon gently holding a mouse that entered her enclosure, bonobos cradling mongoose pups, and macaques riding on the backs of deer. In some instances, groups of primates worked together to groom stray dogs. These behaviors were observed in both wild habitats and captive environments, suggesting they are not solely artifacts of zoo settings or human intervention.

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However, not all encounters were benign. The researchers identified 26 cases classified as abusive, which included a baboon carrying a domestic puppy for extended periods. Thirteen incidents resulted in the death of the non-primate animal due to violent handling. The authors note that these fatal outcomes did not necessarily indicate aggression or ill will; some may have been failed attempts at caregiving by primates unfamiliar with the fragility of the other species.

Patterns emerged regarding which primates initiated these interactions and how they behaved. Juvenile primates were more likely to engage in play, while females showed a higher propensity for grooming behaviors. In the majority of cases, the primate initiated the contact rather than responding to advances from the other animal. This suggests an active interest in cross-species engagement rather than passive tolerance.

The study aims to fill a gap in mainstream scientific literature regarding interspecies relationships among primates. While individual anecdotes have appeared in media reports and niche studies, this compilation provides a broader dataset for analysis. Experts note that previous observations were often treated as scattered curiosities rather than systematic data. By aggregating these cases, researchers can begin to interrogate the frequency and nature of such behaviors more rigorously.

These findings may offer clues about the evolutionary origins of human pet-keeping. The behaviors observed in primates—such as curiosity, tolerance, caregiving, and maintaining relationships with other species—appear to be foundational capacities that did not emerge suddenly in humans. Instead, they likely have deeper roots in our evolutionary history. This perspective aligns with archaeological evidence showing that humans have kept companion animals for at least 12,000 years, with some graves dating back 14,000 years containing remains of cared-for dogs.

Despite these parallels, experts emphasize significant differences between primate interactions and human pet ownership. Most documented cases among primates are ephemeral, lacking the long-term, durable caretaking bonds that define modern relationships with pets. One notable exception involved a group of capuchin monkeys in Brazil that adopted an infant marmoset, providing care for at least ten months. Such sustained relationships appear to be rare exceptions rather than the norm.

The research team hopes their work will encourage further observation and study of these behaviors in both wild and captive settings. By recognizing that cross-species interactions are more common than previously thought, scientists can better understand the social flexibility of primates. This knowledge may also inform conservation efforts and animal welfare practices by highlighting the complex social needs of primates beyond their own species.

Critics of the study point out limitations in the data collection method. Because the observations were not part of a designed experiment, the numbers reflect where scientists and cameras have been rather than the true frequency of these behaviors in nature. The dataset is biased toward locations with high human presence or research interest. Nevertheless, the compilation provides a valuable starting point for understanding the breadth of primate social behavior.

As researchers continue to analyze these interactions, the focus remains on understanding the motivations behind them. Whether driven by playfulness, maternal instincts, or social learning, these cross-species engagements reveal a level of social complexity that extends beyond intra-species boundaries. The study underscores the importance of looking beyond traditional frameworks when studying animal behavior and recognizing the diverse ways animals interact with their environments and each other.

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  • Smithsonian Magazine↗Do Monkeys Keep Pets? Study Finds Widespread Primate Interactions With Other Animal Species, From Mice to Deer