The findings of the study are published in the journal Cell Biology. "An important psychological theory suggests that humans become more socially selective when they know that their remaining life time is limited, such as in old age," Laura Almeling, a biologist at the Leibniz Institute for Primate Research, explained in a news release. "We assume that monkeys are not aware of their own limited future time."
"Therefore, if they show similar motivational changes in old age, their selectivity cannot be attributed to their knowledge about a limited future time," Almeling continued. "Instead, we should entertain the possibility that similar physiological changes in aging monkeys and humans contribute to increased selectivity."
During the study, a group of Barbary macaques were given a variety of novel animal toys by the researchers. Only one toy of featured a food treat. The study showed that adolescent monkeys quickly grew out of their interest in the toys and started moving towards the food-baited object once they matured.
"With increasing age, the monkeys became more selective in their social interactions," Almeling said. "They had fewer 'friends' and invested less in social interactions. Interestingly, however, they were still interested in what was going on in their social world."
"Older females continued to respond particularly strongly to hearing a scream for help from their best friend," Almeling explained. "Older males still looked preferentially at pictures of the newborns", she says, noting that Barbary macaque males use infants as status symbols."