Barbary macaques approaching the end of their life become decreasingly interested in maintaining large groups of friends, choosing instead to focus their social energies on those that are nearest and dearest to them. Similar tendencies have been noted in elderly humans, with one of the leading explanations for this being that, as death approaches, we become more inclined to surround ourselves with those who are most important to us. This new finding, therefore, raises some interesting questions regarding the evolutionary roots of human behavior, as well as whether non-human primates can comprehend their own mortality.
Appearing in the journal Current Biology, this new study reveals how, amongst a group of macaques, older members tend to become increasingly disinterested in the physical aspects of their environment, yet surprisingly do not distance themselves from social stimuli. To determine this, researchers gave the monkeys a number of sparkly, colorful toys such as tubes of glitter and multi-colored cubes, noting that young macaques were much more willing to engage with these than their elders were.
At the same time, monkeys of various ages were shown pictures of other macaques, some of which they had close social bonds with while others were strangers. Interestingly, although elder macaques paid far less attention to photographs of unfamiliar monkeys than their sprightlier counterparts, their interest in pictures of important social partners did not decline with age.
As such, the researchers conclude that the decreasing willingness of elderly macaques to engage with strangers is not a product of a general lack of interest in social information, but of increasing social selectivity.
To back up this theory, they observed the monkeys as their interacted with one another in their natural habitat, finding that older members of the group tended to groom far fewer macaques than younger ones did. However, perhaps somewhat surprisingly, older monkeys were still groomed by the same number of individuals as younger monkeys were, suggesting that their social selectivity is not a product of being shunned by their peers as they age.
Though some may interpret these findings to mean that, like humans, some primates have an appreciation of their own impending death and therefore focus on the important things in life once they sense their time running out, the researchers are reluctant to jump to this conclusion. Instead, they suggest that older monkeys are simply less willing to take risks by engaging with unknown individuals. This, they say, also explains their reluctance to play with the fabulous yet unfamiliar toys.