Aging monkeys become more selective
When we are young, we are curious and eager to gain new experiences. As we get older, we focus on what we have achieved and maintain social relationships with those who are really important to us. Is this increased selectivity due to reduced resources such as vitality? Or, as psychological research on humans suggests, is it due to the awareness that our remaining future lifetime becomes more and more limited as we age, motivating us to focus on the most important things? In order to disentangle the different factors that may contribute to increased selectivity with age, Laura Almeling from the German Primate Center (DPZ) studied Barbary macaques. Combining behavioral observations and field experiments, she tested the behavior of monkeys across adulthood. Her studies show that Barbary macaques also become more selective as they age: Soon after entering adulthood, the monkeys began to lose interest in exploring new objects in their environment. Moreover, the social network size decreases with age. Thus, selectivity appears to be deeply rooted in primate evolution and not tied to an awareness of a limited remaining lifetime (Current Biology).
Laura Almeling and her colleagues from the German Primate Center (DPZ) conducted a study with 118 monkeys aged between four and 29 years in the Monkey Park "La Forêt des Singes" in Rocamadour (France) and carried out behavioral experiments and observations. The reactions of the animals were video recorded and later analyzed in detail.
When the scientists presented novel objects, only young macaques showed keen interest to explore them. To test the reactions of the monkeys to their social environment, they were presented with recruitment screams and with photos of conspecifics. Male Barbary macaques showed a particularly strong interest in photos of newborns. In addition to the interest in newborns, females also looked longer at pictures of friends than of other group members. Moreover, they responded to recruitment screams well into old age, especially when the screams were of their best friend.
"Barbary macaque females do not generally lose interest in social interactions when they grow older. However, they do focus their social activities on a smaller group of partners," says Laura Almeling. This became evident in their grooming behavior: In contrast to the young monkeys that changed their grooming partners very often, grooming in older females occurred in a smaller circle of friends.
Taken together, then, the monkeys lose interest in new stimuli already at a fairly early age, and the focus of older animals is clearly on their social environment. "In this, they are very similar to humans who become more selective as they get older", says Alexandra Freund, who was also involved in the study. "Our research demonstrates the importance of behavioral research in monkeys in order to gain a better understanding of human aging. The behavior of older people has deeper roots in primate evolution than previously thought. Motivational changes in old age do not seem to be primarily dependent on the awareness of a limited remaining lifetime”, concludes Julia Fischer, the principal investigator of this research.
Laura Almeling, Kurt Hammerschmidt, Holger Sennhenn-Reulen, Alexandra M. Freund, Julia Fischer (2016): Motivational shifts in aging monkeys and the origins of social selectivity. Current Biology http://www.cell.com/current-biology/fulltext/S0960-9822(16)30460-2, DOI: http://dx.doi.org/10.1016/j.cub.2016.04.066