Ageing brings new horizons Mark MacEwen/Naturepl.com

Do you see as many friends now as you did 10 years ago? Your shrinking social circle isn’t just a human trait – it seems that, as they get older, monkeys become more selective about who they spend time with too.

We have known for decades that older people are generally less sociable than young adults. This used to be considered a bad thing – a sign that older adults become cut off from society and lonely. But on quizzing them, researchers found that older adults were generally no more likely to report being depressed or lonely than college students. As a general rule, people actually seem to choose to be less socially active as they age.

“It’s not that they don’t like to interact with people, but given a choice they will interact with people they know and like – people who have more emotional meaning in their lives,” says Susan Charles at the University of California, Irvine.


Best friends

Now Julia Fischer at the Leibniz Institute for Primate Research in Göttingen, Germany, and her team have found that some monkeys do the same. Observing free-roaming Barbary macaques living in a wildlife park in southern France, they found that the macaques spent less time grooming other monkeys as they aged, and groomed an ever-shrinking number of individuals.

They found that elderly, 25-year-old macaques spent less than half as much time grooming as 5-year-old adults, and tended to about half as many monkeys.

“I think the study is fantastic – really interesting,” says Charles. “It opens the way to looking at the biological or physiological mechanisms that might be at work.”

To explain this trend in people, psychologist Laura Carstensen at Stanford University came up with an idea called socio-emotional selectivity theory (SST). Her research suggested that the key factor behind social change as we age is a growing appreciation that our time is precious and limited.

This idea is supported by surveys in which older adults said they would be more likely to make new friends if they knew they had more decades to live. Conversely, if younger adults are told to imagine they are about to move to a new part of the world, they say they would rather spend the limited time left in their current location socialising with existing friends than making new ones.

Risk-averse

“SST does describe and accurately predict human behaviour,” says Fischer. But her findings suggest this is not the whole story.

“I don’t think monkeys have any awareness of their death, so if there are any changes in their behaviour, they’re obviously not to do with that,” says Dario Maestripieri at the University of Chicago, Illinois. “Maybe we would behave similarly even if we had no awareness of our own death.”

Fischer thinks the more selective socialising of older monkeys may be a sign that they are becoming more cautious. “The old monkeys become increasingly risk-averse, so they avoid unpredictable interactions. But we need to test this with more data,” she says.

Yet if the thought of losing friends as you age upsets you, fear not. Just like some people, a few monkeys in the study bucked the general trend, remaining sociable into their old age.

Journal reference: Current Biology, DOI: 10.1016/j.cub.2016.04.066

Read more: Friendship: Do animals have friends, too?