Assamese macaques show how aging affects our social networks

Aging and social networks undergo significant transformations as individuals grow older, with a pronounced shift towards prioritizing quality over quantity in their social circles. This tendency to narrow down social connections is not exclusive to humans; it is also evident among our primate relatives, the macaques.

The phenomenon, as observed in Assamese macaques in Thailand by researchers from the German Primate Center – Leibniz Institute for Primate Research and the University of Göttingen, provides insight into the biological foundations underlying our social behaviors.

Understanding social aging through primate studies

Over eight years, researchers studying female Assamese macaques observed a decline in social network size with age. Consequently, older females focused on a few close relationships and reduced broader interactions.

Baptiste Sadoughi, the study’s lead author, emphasized the unique perspective gained from studying these females. Significantly, they remain in their natal groups for life.

Moreover, older macaques showed less social engagement, such as initiating contact or grooming. However, they stayed close to the group, likely for protection against predators. This behavior indicates a strategic shift in aging macaques’ priorities, valuing proximity over active socializing.

Social selectivity among Assamese macaques

Contrary to what might be expected, the research showed that selectivity in social partners among Assamese macaque females does not increase with age.

This constancy undermines the idea that a growing preference for certain social partners explains the age-related shrinkage of social networks. This finding suggests that while selectivity exists, it alone cannot account for the decline in social interactions as macaques age.

The role of longitudinal data in aging studies

The study highlights the value of longitudinal data in aging research. Professor Julia Ostner notes that the selective disappearance phenomenon complicates aging studies.

Less socially integrated individuals, who are more vulnerable to predation, tend to die earlier. This leaves a cohort of older, well-connected individuals. Long-term data helps differentiate true aging effects from demographic influences.

Aging and social networks in the wild

This research significantly enhances our understanding of aging in wild animals, challenging the traditional belief that they seldom show aging signs. Sadoughi points out that long-term studies are uncovering how wild animals face aging challenges, providing insights into their adaptations over time.

The study on Assamese macaques illuminates social aging’s evolutionary roots and its parallels with humans, who also narrow their social networks with age. Examining our closest relatives offers profound insights into social aging’s complexity and its impact on our social world.

More about Assamese macaques

Assamese macaques are a species of Old World monkey found predominantly in the hilly and forested regions of South and Southeast Asia. 

Appearance

With their robust build and distinctive appearance, they are known for their strong social bonds and complex behaviors. 

Their fur color varies from dark brown to gray with a somewhat lighter underbelly, and they have a prominent ridge of hair on their heads, which gives them a unique appearance among primates. These macaques have relatively short tails and show a range of facial expressions that are crucial for their social interactions.

Habitat

They are highly adaptable, living in a variety of habitats including evergreen forests, deciduous habitats, and even areas close to human settlements, where they can sometimes be seen foraging for food. 

This adaptability, however, also puts them at risk, as they are often subject to human-wildlife conflict, especially in areas where their natural habitats overlap with agricultural or urbanized areas.

Diet

Assamese macaques are diurnal, meaning they are active during the day, and they have a diet that includes fruits, leaves, seeds, and occasionally small animals and insects. Their foraging habits play a crucial role in forest ecology through seed dispersal, aiding in the regeneration of their habitats.

Social lives

Socially, Assamese macaques live in multi-male, multi-female groups with a complex social structure. Dominance hierarchies exist within both males and females, influencing access to resources, mating opportunities, and social interactions within the group. 

These macaques are known for their cooperative behavior, including collective defense against predators, grooming to maintain social bonds, and caring for the young of the group.

Reproduction 

Reproduction in Assamese macaques does not follow a strict seasonal pattern, but births may peak at certain times of the year, depending on the geographical location and environmental conditions. Females usually give birth to a single offspring after a gestation period of about six months.

Offspring are cared for with great attention, and the social nature of their groups allows young macaques to learn important survival and social skills from not only their mothers but also other members of the group.

Conservation

Conservation efforts for Assamese macaques are ongoing, as they face threats from habitat destruction, hunting, and the illegal wildlife trade.

Their status varies by location, but overall, they are considered to be facing a decline in population, prompting efforts to protect their natural habitats and ensure their survival for future generations.

The full study was published in the journal Proceedings of the Royal Society B Biological Sciences.

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