Like humans, older rhesus macaques have fewer social contacts

Scientists note that older rhesus macaques interact almost exclusively with close relatives. A little like the elderly. So groups of monkeys show the social consequences of aging in human societies.

Robin Goldsmith

When female rhesus macaques grow up, they no longer need to be the center of the group. In fact, they back off a bit. From now on, they are committed to interacting with their immediate family.

Scientists at the University of Exeter describe this reticent behavior in older rhesus monkeys in the journal Philosophical Transactions of the Royal Society b. For the study, they spent years observing monkeys on the island of Cayo Santiago, southwest Puerto Rico. A large population of rhesus macaques has lived on the island since the 1930s and is regularly studied.

The fact that older monkeys take it a little easier socially seems to be their own choice. And the researchers noted that their group did not reject them. Older adults don’t necessarily spend less time with their peers, either. Only the number of social contacts decreases.

Too tired for a big social network

The scientists suggest that perhaps older animals isolate themselves because they are less likely to become infected. Or, as researcher Irene Siracusa believes, perhaps the older apes are just a little tired. “New relationships are mentally demanding. Thus, older monkeys save energy by reducing their social network.”

Researchers believe that young macaques may also benefit from many different social contacts than older ones. For example, to gain knowledge about the environment or to find a partner.

For a group of rhesus monkeys as a whole, the researchers believe that the withdrawn behavior of older females has drawbacks. After all, knowledge gained by older animals in their lifetime is reaching fewer congeners in their shrinking web.

Many studies have investigated the relationship between age and social behavior in animals. In killer whales, the older, postmenopausal female has a leadership role in the group. They have the most knowledge and experience and teach young animals how to find food. Therefore, female killer whales have a whole life ahead of them after menopause. Their presence improves the chances of children (grandchildren) surviving.

As the population ages, the bond between the group is less close

If a particular age group is over-represented, this has consequences for pedigree in a group of animals. In orca populations where young animals are missing, the bond between all animals is less close. And in places where bounty hunters have shot many elephant bulls, the remaining males are more aggressive towards safari cars and humans.

It is not only animals that sometimes live in groups where the ratio of old to young is unbalanced. There are also relatively large elderly populations in many populations, such as in the Netherlands. Older adults, such as older macaques, often have fewer social contacts.

The groups of rhesus monkeys now studied consist of about 20 percent of the older animals. Computer simulations show that if there are more older individuals present, the social cohesion in the group decreases. It is conceivable that a similar effect would occur in aging human societies. According to scientists who have studied monkeys, the social effects of aging are probably “extremely far-reaching.”

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