Monkeys become more selective about who they hang out with as they grow old, a new study suggests. The research, published in the Cell Press journal Current Biology, was led by a team from the German Primate Center in Goettingen, Germany.

Researchers studied a group of Barbary macaques of various ages and found that the species experience changes in their behavior as they age. As human beings do, they become particular about how they spend their time, and in particular with whom they spend it.

Researchers found more picky behavior among older monkeys as their 'friend' circles start getting smaller as time goes by. Image Credit: Cinema Blaze
Researchers found more picky behavior among older monkeys as their ‘friend’ circles start getting smaller as time goes by. Image Credit: Cinema Blaze

These findings may lead to a new evolutionary insight on why aging humans become isolated, researchers say.

The scientists focused on a sample of more than 100 monkeys, aged from 4 to 29, kept in the enclosure “La Forêt des Singes”, a park located in Rocamadour, France.

Dr. Julia Fischer, one of the leaders of the research team, told the New York Times that they noticed that the older the monkeys were -beginning at the age of 20- the less likely they were to engage social contact with the other animals, like playing or fighting. To study and record the levels of monkeys’ curiosity, they introduced the animals to objects like pet toys or a tube containing food. Adult monkeys would show less interest in toys and focus on the tubes baited with food.

Getting ‘out of the box’ from standard experiments on animals

Researchers also implemented other experiments, like exposing the animals to recorded screams and calls, and even photographs of other monkeys. They maintained curiosity on their environment, but without directly involving with it, while they showed less interest on other primates, except for a few, which they consider their close “friends.”

According to a statement released by Fischer, the “older animals might spend less time socializing because they find social interactions increasingly stressful and therefore avoid them.”

Human socio-emotional selectivity theory wouldn’t explain the similar behavior of macaques

Psychologists describe the isolating tendencies of aged humans with the socio-emotional selectivity theory. This theory says that as we age, we become closer to our emotionally important partners since we get more aware that our lifetime is continuously decreasing. For monkeys, this should not be the case.

“We assume that animals are not aware of their own limited time,” researcher Dr. Laura Almeling stated at the study release.

Instead, they attribute physiological changes to the increased selectivity. Like for humans, aging brings physical losses to monkeys.

Therefore, authors speculate this would make the monkeys less disposed to take risks, assuming encounters with unfamiliar animals means taking a chance on them. Another explanation the researchers shared with the New York Times is that socializing becomes exhausting activities for the monkeys, so they stick to the most comfortable relationships they already have.

 

These findings accentuate the importance of primate species as models for studying the behavior of humans. Results suggest that our tendencies to become more personal while aging may be more because of a biological reason than a social one, stretching the link between both species, Alexandra Freund, a psychologist at the University of Zurich, told the Times.

Source: NY Mag