This phenomenon is observable in many primates, and especially in humans, even though they know how to compensate for it, recalls a study published in Proceedings B of the British Royal Society. Who notes that this topic is all the more interesting that the human population is rapidly aging, according to the United Nations, in 2050 there will be 2 billion people over 60 years old.
As we age “limited to a smaller circle of people”
Research that posits that maintaining social ties in old age is a factor in good health is still debating the reasons for this disengagement. The observation is that as we age “limited to a smaller circle of people”explains AFP ethologist Baptiste Sadoughi, first author of the study published on Wednesday.
Individuals would thus prioritize the quality of relationships rather than their number, according to the theory of socio-emotional selectivity developed in the 1990s, specifies this doctor of behavioral ecology at the German University of Göttingen and at the Leibniz Institute for Primate Research (DPZ ).
The problem with humans is that behavioral studies are based on cross-sectional samples, meaning that age groups are mixed at the same time. A method introducing inevitable biases.
The interest of the study carried out by the DPZ team was to monitor the population of primates, macaques of Assam, longitudinally, that is, over time: the behavior of 61 females between the ages of 4 and 30 was observed over several years between 2013 and 2021. , living freely in a Thai reserve.
With several findings without appeal. Increasing social isolation with age, “with halving the size of the average social network between a ten- and twenty-year-old woman”according to Mr. Sadoughi.
Partially intentional isolation
This measurement in the macaque is done by evaluating mutual grooming practices, the preferred way of relating in this primate species, in the absence of mastery of bridge or bingo.
The observation ruled out that this isolation was the result of spatial segregation, because even when old, macaques maintain physical proximity with their conspecifics. Their relative isolation is partly intentional: “The aging individual is responsible for much of these changes because they approach others less and initiate fewer body-to-body interactions.”
Isolation also suffered because with age, the female macaque “fewer and fewer individuals will be dewormed”. It will remain so despite its faithful friends, notes the ethologist, “Mostly interacting with the same individuals she’s always interacted with more often or better.”
Assamese macaques would thus be subject to the phenomenon of social selectivity, but with a substantial difference compared to humans, as the latter compensate for the narrowing of their circle of relationships by more extensive exchanges with their loyal friends.
This second phenomenon of social selectivity has so far been observed through a 2022 longitudinal study in a population of rhesus macaques that focused their socialization efforts on a limited number of partners.
This 2022 study, whose only drawback was that it focused on a population in semi-freedom, concluded that social selectivity would “deeply rooted in primate evolution”.
Baptiste Sadoughi thinks that this social selectivity will not be the prerogative of only humans, but “an aging coping strategy that has probably always existed since we were primates”man and macaque.