When it comes to figuring out which individual among a group of primates is the most dominant, some scientists simply look for the one that’s being the most assertive or aggressive. New research suggests this approach grossly underestimates the social complexity of nonhuman primates, and that there’s more to social dominance than being a bully.
The social relationships of nonhuman primates, and the ways in which social dominance is achieved, maintained, and perceived, are more complex than scientists have traditionally assumed, according to new research published this week in Scientific Reports. The research also shows that existing techniques for observing and measuring dominance among nonhuman primates, whether they be monkeys or apes, are insufficient and lacking in sophistication. The authors of the new study, a team led by anthropologist Jake Funkhouser from Washington University in St. Louis, say new observational and analytical tools are needed to better understand “the layers of diverse social relationships we see in the animal kingdom, our own human societies included.”
Indeed, as primatologists such as Jane Goodall, Dian Fossey, and Frans de Waal have shown, primates engage in complicated social behaviours. Unfortunately, however, many of the methodologies used to observe and assess the power struggles that exist among primates, such as monitoring scenes in which individuals fight over food or sexual partners, are far too basic, according to the new research. As Funkhouser and his colleagues point out, these methods are consistently failing to capture some of the finer details involved in the big picture, and the “extremely complicated, nuanced, and multi-faceted” dynamics that typically transpire in primate relationships, as Funkhouser put it.
Wild juvenile Tibetan macaques. Image: Jessica Mayhew.
“The social relationships humans share with others cannot be accurately represented in simply ‘dominant’ or ‘subordinate’ terms,” explained Funkhouser in a press release. “Nor do our relationships readily transfer between settings; the aggressive or confrontational interactions we engage in with some are much different than the prosocial interactions we share with our spouse and best friends.”
Like human relationships, primate relationships are highly individualised; they vary according to the individuals involved (e.g. every one-on-one relationship is unique), and the social context within which the interactions are taking place. In humans, for example, the tone of our relationships varies depending on the setting, such as when we’re at work with colleagues or lounging at home with our friends and family. The same goes for nonhuman primates, though the contexts are obviously different.
A core finding of the new study is that scientists are oversimplifying the term “social dominance” when using it to describe the behavioural characteristics and power status of primates. Not only that, but scientists frequently use different definitions of dominance in their studies, and use different measures and statistical techniques to detect levels of dominance within a group.
Funkhouser and his colleagues discovered this by conducting a comparative analysis of the techniques used to measure dominance among a group of captive chimpanzees at Chimpanzee Sanctuary Northwest in Washington state and a group of wild Tibetan macaques in China. The researchers observed both of these groups, collected data, and then applied their findings to 69 different statistical techniques commonly used to rank an individual’s status within a group. By comparing and contrasting the results provided by each of these methodologies, the researchers found a startling “lack of reliability or predictability” between the techniques.
Take, for example, a pair of observations made of two chimps, Jamie and Negra.
Jamie, a 38-year-old female chimp, is quite aggressive. But is she socially dominant? Image: Chimpanzee Sanctuary Northwest
Jamie, an adult female chimp who is retired from use in medical research, is often aggressive toward other chimps. Observational methodologies that recognise dominance through physical competition calculated Jamie to be the most dominant within the group. But then there’s Negra, an older adult female chimp who was also retired from research. Negra rarely gets involved in physical shenanigans, but she is the chimp most frequently groomed by other member of her group. So observational methodologies that track an individual’s ability to procure desired resources, in this case grooming, ranked Negra as being in the most privileged dominant role. Taken together, these examples of Jamie and Negra point to the complex and fluid nature of chimpanzee social systems, and the importance of looking beyond simple, one-dimensional behavioural measures.
Observations made of the macaques were a bit different, but equally illuminating. Macaques, unlike chimps, maintain a single dominance hierarchy that sticks, regardless of the social context. During observations, for example, two young adult males were consistently the most dominant, while two females were consistently the least dominant. This particular observation underscores the importance of understanding the nuances and quirks of the species being studied. Macaques are monkeys, not apes, so scientists shouldn’t expect their behaviour, or their social relationships, to be particularly ape- or human-like. In their study, the researchers say “comparable, yet species-specific, data collection methods and statistical analyses between authors and investigations are necessary to maximise the collection of dominance interactions and generate commensurate results.” In other words, methodologies used to study chimps, bonobos, or gorillas, shouldn’t necessarily be used to study macaques. And vice-versa.
“The perception that dominance is solely about aggression, in other words who ‘wins’ and who ‘loses’ a contest, is only one piece of the larger group social dynamics.”
Funkhouser and his team say new techniques and deeper investigations of context-specific dominance are needed, and that researchers need to move away from single, linear ranking orders of individuals based on single measures, such as competitiveness. They admit that this broader, more detailed approach will be more time-consuming, and it’ll require different types of behavioural data, but it’ll be more effective at “providing a holistic lens for depicting dominance relationships in nonhuman primate groups,” and it could also “accurately reflect how nonhuman primates use dominance relationships in fluid, situation-specific ways in the ever-changing social groups they live in,” the authors write in the study.
These latest findings are consistent with research done in 2014 by researchers from the University of Oxford, who found that social dominance among primates was not solely determined by an individual’s strength or aggression, but also in how they formed bonds and forged alliances.
Jessica Mayhew, a co-author of the study and an assistant professor of anthropology and museum studies at Central Washington University in Ellensburg, said the new paper is highlights the fact that social context matters for social animals.
“The perception that dominance is solely about aggression, in other words who ‘wins’ and who ‘loses’ a contest, is only one piece of the larger group social dynamics,” said Mayhew in a statement. “It’s critical that as researchers we continue to acknowledge the context in which we collect our data because it influences our interpretation.”
Scientists’ approach to studying primates has obviously improved over the past 50 years (Jane Goodall, as an example, was criticised in 1960 for naming the chimps she observed, instead of the more conventional practice of assigning numbers to them). But as this new research shows, there’s still plenty of room for improvement. Like humans, primates are complex — and our science has to reflect that. [Scientific Reports]
Featured image: Jessica Mayhew