Study of Old Monkeys Provide Clues to Why Aged Humans Behave the Way They Do

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Credit: Julia Fischer/German Primate Center

Our social interactions are dependent on age and as we grow older our social preferences change and that’s one of the traits that has been a focus of many studies. A new study recently published in Cell Press journal Current Biology looks at this by studying old Barbary macaques to garner an evolutionary perspective on why aging humans behave as they do.

Researchers studied Barbary macaques’ selectivity regarding their interest in the nonsocial and social environment through a large sample of more than 100 monkeys of different ages kept in the enclosure “La Forêt des Singes” in Rocamadour.

Researchers offered monkeys with novel objects such as animal toys, a cube filled with colorful plastic pieces in a viscose liquid, and an opaque tube closed with soft tissue at both ends and baited with a food reward to study their curiosity to explore new things. Experiments showed that by early adulthood, the monkeys had lost interest in the novel objects. Only the tube containing food held interest for all but the oldest monkeys.

In a bid to understand the monkeys’ social interests, scientists showed monkeys photographs of newborn monkeys, “friends” and “non-friends” and played recorded screams of “friends” and “non-friends.” Further, scientists also observed how often and how long monkeys interacted with each other.

One of the findings was that aging monkeys maintained a keen interest in other monkeys, especially when the other monkey was a socially important individual. Older females continued to make vocalizations in response to interactions of group members in their vicinity, such as infant handlings or conflicts. However, older females engaged in fewer social interactions, although other group members continued to invest in relationships with them.

Researchers found that as they aged, monkeys became more selective in their social interactions. They found that old monkeys had fewer ‘friends’ and invested less in social interactions. Overall findings indicate that like humans, monkeys become more selective as they age.

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