인간은 왜 반려동물을 기를까?… 원숭이도 닭 기르고 생쥐 쓰다듬는다

Human beings have long wondered why they are the only species to keep companion animals. A new study suggests that this unique behavior may be rooted in our primate lineage. Researchers from the University of Oxford analyzed how primates interact with other species and found that this social behavior is far from exclusive to humans.

The study, published in the journal Primates last month, reveals that primates exhibit various social interactions with different animals, including grooming, carrying, and even sharing food with non-primate species. A notable example is "Koko," a gorilla who, in 1984, formed a bond with an adopted cat named "All Ball." The same year, Koko was reportedly seen crying when her cat friend passed away due to a road accident.

In Israel, a capuchin monkey was observed protecting a chicken in its enclosure in 2017, while in Japan, a Japanese macaque was seen riding on a flying squirrel. Despite these observations, systematic research on interspecies interactions remains limited. Dr. Silvestro Garutta, an anthropology professor at the University of Oxford and a co-author of the study, noted that it is unusual for humans to lavish resources on unrelated species, suggesting that this behavior could stem from a need for social connection.

The oldest known evidence of humans keeping pets dates back 14,000 years, featuring a man and a dog buried together in a German grave. Dr. Garutta, who first conceived the idea during his master's studies at the Shenzhen Primate Center in China, recalled observing a female long-tailed monkey gently holding and carefully stroking a small rat, carefully cradling it in her hands.

The researchers compiled 427 instances of interspecies interactions from previous academic research, news articles, and surveys of primatologists, encompassing 88 primate species in both wild and captive settings, alongside 127 non-primate species (mammals, birds, reptiles, amphibians, arthropods). While most interactions were playful and grooming behaviors, even distantly related species like dogs and chickens displayed signs of attachment.

The most common behavior was play and grooming, with juveniles engaging in play and adult females more frequently engaging in grooming. Adult males, however, were less likely to engage in close interactions and were occasionally aggressive. However, some cases suggest that these relationships resembled adoption. The study suggests that companionship, care, and exploration are likely more prevalent among primates than previously thought.

So why do primates engage in interactions with unrelated species? Dr. Garutta hypothesized that loneliness could be one motivation, similar to how humans might seek comfort from others when feeling lonely.