To our human eyes, a mouse’s furred face doesn’t betray much emotion. But if you watch the body language of a mouse who’s reunited with one of her sisters after five days in a cage alone, you might suspect you know what she’s feeling.
The formerly isolated mouse chatters in squeaks too high for a human to hear. She follows her sister, crawling beneath the other mouse’s body as if trying to get a hug. She looks like she’s feeling what you or I feel when meeting a long-lost friend or a family member — maybe with more sniffing.
She looks like she’s been lonely.
Loneliness isn’t just for humans, and neither are its harms. Knowable Magazine explored how over the past decade or so, some researchers have come to believe that an animal’s craving for the company of others isn’t just a preference, but a basic, deeply held need. When we don’t socialize enough, we feel the lack like hunger or thirst, they say. When we’ve had our fill of togetherness, we feel satisfied or quenched.
The amount of socializing a creature needs may be particular to that species, and even to that individual. Scientists have found within-species social differences in birds, monkeys, fish and even cockroaches.
Among humans, “you can feel lonely at a party, or you can feel fine alone in your office,” said Kay Tye, a neuroscientist at the Salk Institute for Biological Studies in California. Whatever the ideal degree of togetherness, Tye and others think that an animal’s need to balance time alone and time with others represents a kind of homeostasis: an equilibrium that’s critical for survival. Today, they are on a hunt to find where, in the brain, this equilibrium is controlled — and hoping their work will hold dividends for lonely humans.
A range of socializing
Beavers live with their immediate families. Starlings flock in huge murmurations. Adult male orangutans roam solo until it’s time to find a mate. What determines an animal’s ideal amount of socializing?
Tim Clutton-Brock, an evolutionary biologist retired from the University of Cambridge, says several factors can push species to become more or less social as they evolve. One is the need to keep warm. Another is foraging: Does searching for food in a group make it easier for that animal to eat, or harder? What about predation — is there safety in numbers, or is it better to be alone and inconspicuous? Do females need help from others to raise their young?
“Dealing with the neighbors” is also important, Clutton-Brock said. For example, the meerkats he studies in the Kalahari Desert live in territorial groups, and constant conflict means it’s better to live in packs. A wild meerkat who’s separated from the group is visibly distressed and looks around constantly. “They very clearly get extremely worried,” he said.
Within each species, Clutton-Brock says evolution has probably allowed for a range of personality types around a certain species average. “There are costs to too much anxiety” about being alone, he said, “and costs to too little anxiety.” A species may do best with a mix of social styles.
Whatever an animal’s right amount of social activity, research suggests there can be dire consequences to mental and physical health when it’s not met. People who a