Jessica Flack's time as a graduate student at Emory University has given her a platform from which to contemplate evolutionary biology — quite literally. She spent 5 months doing 12-hour shifts watching pigtailed macaques from a vantage point 8 metres off the ground.

Her aim was to learn how the macaques resolve conflicts within their group, but the task was not straightforward. First Flack needed to be able to identify all 84 macaques in the group by sight. Then she had to learn the signs that showed a dispute was brewing — and wait for the conflicts to arise. “It takes a lot of patience,” Flack says, “because most of the time the animals aren't doing anything.”

It's remarkable, all the dominant males have to do is approach the conflict and it breaks up.

Flack undertook this sometimes “gruelling” enterprise because she wanted to explain how fairly complex social interactions emerge among the macaques. She learned, for example, that over time a few monkeys gain dominant status through fighting.

“One of the most interesting behaviours is the policing function performed by some of these very powerful males,” Flack says. “It's remarkable, because when a conflict erupts, all they have to do is approach the conflict and it breaks up; they usually don't have to show any aggression.” Although this policing function manifests simply, it takes many complex interactions to build up.

Flack was especially fascinated by the way the animals created a social system with a set of rules that can be modelled. “These behaviours are learned by individuals,” Flack says. “And social structures persist when these individuals are gone.”

To find out how, Flack concentrated on aspects such as displays of aggression and signals of submission that seemed to build into a social network. For example, she saw that individuals who have lost a fight to another member will silently bare their teeth when approached by the past victor, in effect indicating ‘I recognize that I am subordinate’. She also saw that active policing by a third party happened in only about 15% of conflicts — but that its potential had broad implications for social organization, including how individuals build their social networks.

Flack enjoyed observing the social interactions, despite the long hours. But the challenge was to go beyond observation into theory. To do so, she borrowed the idea of knocking out a gene from developmental genetics and instead disabled a behaviour, in this case, policing. She needed to turn a complicated set of interventions, status signalling and conflict-related behaviours into data that could be coded systematically and would be amenable to social-network analysis.

Once she had completed her observations, Flack moved to the Sante Fe Institute in New Mexico, where she focused asking what she calls “the robustness question” — in other words, how do these social behaviours persist over time?

“At first it wasn't clear what these data meant and what statistics were appropriate for this network,” she says. But part of the satisfaction was cracking this problem and finding a set of mathematically sound rules that have implications for evolutionary biology.

Next, Flack plans to look at other rules of social organization in macaques in the hope of modelling interactions between larger groups.