A study published on August 18, 2026, in the journal Primates has shown that the roots of pet-keeping behavior run deep in primate evolution. Scientists analyzed 427 interspecies interactions across 88 primate species and discovered that each species exhibits behavior that can be linked to caring for other animals, much like humans do with pets.
A particularly striking example is the troops of stump-tailed macaques in Thailand, which regularly groom and care for local dogs. Scientists have observed such interactions repeatedly: the macaques approach the dogs, clean their fur, and spend time nearby without showing aggression. Similar cases have been recorded among chimpanzees in Uganda, which affectionately groomed the tail of a red-tailed monkey.
Primate behavior toward other species challenges previous notions about evolutionary benefit. As psychologist Hal Herzog of Western Carolina University noted, expending resources on animals of another species seems disadvantageous, yet it occurs ubiquitously. Researchers suggest that the desire to care for other living beings may be innate to primates, including humans.
Cases such as Koko the gorilla and her kitten were already known, but the new work systematizes data across many species. The behavior varies from simple grooming to more prolonged interaction, and it is observed even in young individuals.
The study's results help to better understand why humans keep pets and how this behavior might have emerged during evolution. It shows that caring for other species is not a unique trait of Homo sapiens, but rather an older characteristic of primates.
