Our daily interactions — whether they be in-person or remote — can involve dozens of other people. But chances are, you only consider a few of those people to be your closest friends.
The same seems to be true for gorillas, new research on their social circles suggests. The findings add to growing evidence of striking similarities between human and gorilla social networks.
A study published Tuesday in the journal Proceedings of the Royal Society B examines social relationships among 13 mountain gorilla groups over 12 years. The gorillas studied live in a national park in Rwanda.
Gorillas typically live in groups of 12 to 20 individuals. That's also the range where researchers found gorillas had the most robust range of relationships. As group size grows — they can go up to around 65 gorillas — the relationships don't become more diverse, the research shows.
Instead, most of the relationships in those bigger groups are weak — suggesting that gorillas, relatably, have a limit to the close ties they maintain.
Robin Morrison, a postdoctoral researcher at The Dian Fossey Gorilla Fund, led the study.
Morrison tells Inverse that the decline of close relationships in the largest groups mirrors that in humans and other social animals where there are "a small number of strong social relationships and progressively larger numbers of weaker ones."
One possible reason for this trend is convenience. "The time and investment we need to put into maintaining strong relationships might limit the number we can have," Morrison tells Inverse.
This challenges the idea that large groups equal more complex social networks, Morrison says. That idea has been discussed before, but before now, it hadn't been directly tested. And while Morrison expected that size and closeness weren't directly linked, it came as a surprise that the diversity of social relationships actually declined as groups grew.
In all, Morrison's team characterized seven relationships between gorillas. Those range from the extreme closeness of a mother and child to decidedly weak associations.
The findings point to just how complex gorilla social groups are, Morrison says. Social preferences, for instance, make up a key part of gorillas' social structure.
"Some young gorillas will have very close relationships analogous to human friendships," Morrison explains, "whilst others may have very weak relationships, rarely playing together or being near to each other." Interestingly, those choices aren't simply defined by a gorilla's age or sex.
Gorillas also all "aren't experiencing group life in the same way," Morrison says. Some have a more diverse range of relationships they keep compared to others. Gorillas' social demands seem to change as they age — for males in particular — "so there may be periods of their lives that are far more socially demanding than others."
Wild observation and conservation — Researchers can learn a lot about how gorillas interact just by watching.
"Gorilla groups are pretty fascinating to watch because of all the different social interactions going on," Morrison says, "at least when they're not napping." She particularly enjoys watching young gorillas hanging out, whether that's wrestling, chasing each other around a tree, or rolling down a hill.
Certain young gorillas may end up at the center of the action, while others get left on the sidelines, Morrison says — "often a younger sibling that's not made it in with the older ones yet" — an all-too-familiar experience among human younger siblings.
Getting to know gorillas' social habits can also give researchers clues about a major threat to the animals: the spread of disease.
"A key next step for us is now to look at how these different relationships influence gorillas' potential exposure to different diseases and how quickly they could spread through a group," Morrison says.
Outbreaks in gorilla populations like ebola, Covid-19, or other respiratory infections can be devastating. More information about social behavior "could help inform our response to that and any potential intervention strategies," Morrison says.
Abstract: Social complexity reflects the intricate patterns of social interactions in societies. Understanding social complexity is fundamental for studying the evolution of diverse social systems and the cognitive innovations used to cope with the demands of social life. Social complexity has been predominantly quantified by social unit size, but newer measures of social complexity reflect the diversity of relationships. However, the association between these two sets of measures remains unclear. We used 12 years of data on 13 gorilla groups to investigate how measures of social complexity relate to each other. We found that group size was a poor proxy for relationship diversity and that the social complexity individuals experienced within the same group varied greatly. Our findings demonstrate two fundamental takeaways: first, that the number of relationships and the diversity of those relationships represent separate components of social complexity, both of which should be accounted for and second, that social complexity measured at the group-level may not represent the social complexity experienced by individuals in those groups. These findings suggest that comprehensive studies of social complexity, particularly those relating to the social demands faced by individuals, may require fine-scale social data to allow accurate comparisons across populations and species.