Whether you've spent time around an aging family member — or maybe you're getting up in years yourself — you know people often get pickier as they age. Apparently, monkeys share the same crotchety tendency.
Researchers from the German Primate Center in Goettingen, Germany, wanted to see how age impacted behaviors on 118 Barbary macaque monkeys living in the 50-acre "La Forêt des Singes," a monkey reserve in Rocamadour, France. They studied the behaviors of monkeys ranging in age from 4 to 29 years which, one of the researchers told the New York Times, is equivalent to about 105 in human years. The study was published in the journal Current Biology.
The researchers offered the monkeys new objects to play with, but only the younger monkeys showed interest. That's similar to how older people may prefer their familiar objects and routines and not want to experiment with new ones.
To look at social interests, the researchers showed the monkeys pictures of newborn monkeys, "friends" and "non-friends." They also played recorded screams of monkey "friends" and "non-friends."
The researchers found that the monkeys were aware of what was going on and responded to photos and screams, meaning they still cared about the social interactions of their group, especially when they involved their closest friends. However, they were less likely to make overtures or get involved as they aged. This was also reflected in the monkeys' grooming behavior. While younger monkeys tended to change grooming partners on a more regular basis, older monkeys tended to stick with the same circle of grooming friends.
"Barbary macaque females do not generally lose interest in social interactions when they grow older. However, they do focus their social activities on a smaller group of partners," says researcher Laura Almeling.
That behavior is typically mirrored in older people who tend to interact with a smaller circle of friends and family, becoming pickier as they age. One theory is that as people age, they realize time is limited and they tend to be more selective about choosing who to spend time with.
However, there's no evidence that monkeys are aware that their days are coming to a close. So if monkeys and humans are acting the same way, it may just be a natural behavior with biological roots, principal investigator Julia Fischer told the New York Times.
"Our research demonstrates the importance of behavioral research in monkeys in order to gain a better understanding of human aging," Fischer said in a press release. "The behavior of older people has deeper roots in primate evolution than previously thought. Motivational changes in old age do not seem to be primarily dependent on the awareness of a limited remaining lifetime."