Older humans become more selective about how they spend their time and who they choose to spend it with. This was generally attributed to humans being aware of their aging and limited time left. New research shows that this isn’t a human trait, aging monkeys change their behaviors as well.
Scientists from the German Primate Center in Göttingen, Germany observed 100 Barbary macaques of various ages. They first wanted to test whether or not aging monkeys lost interest in their nonsocial environment. The monkeys were provided with novel objects, such as a cube filled with colored pieces of plastic floating around in a liquid. Only young adult and juvenile monkeys showed interest in these toys, the older monkeys generally ignored them. The oldest monkeys only interacted with the toys if food was involved, such as a tube containing treats.
To test social selectivity, the researchers used observational studies. They discovered that older monkeys continued to interact socially but were more selective about who they interacted with. Older females were less likely to seek out social interactions when compared to younger females but other monkeys sought out and continued to spend time with them. The researchers also showed the monkeys photos of their “friends” as well as monkeys that weren’t considered “friends”. In a separate trial, they played vocalizations of both friends and non-friends. The older monkeys continued to be interested in monkeys they were friendly with but were more likely to ignore photos and sounds from monkeys that they weren’t close to. This showed that the older monkeys continued to participate in social interactions but were more discriminatory about with whom they spent their time.
The authors note that this shows that primate studies can be useful for studying the behaviors of aging humans. The monkeys are unlikely to realize that they’re running out of time; these behavior adaptations may be brought on by physiological changes. The researchers intend to conduct future studies to analyze cognitive performance and other changes triggered by aging.
Almeling et al. Motivational Shifts in Aging Monkeys and the Origins of Social Selectivity. Current Biology (2016).