Barbara J. King

Friday Animal Blog

Rhesus Monkeys Watch Movies—and Learn about Dominance

November 19, 2010

Look at any kids’ playground – or adults’ corporate boardroom-- and the fact becomes obvious: Hierarchy and status-striving are part of primate living.

Not all primate species are arranged into hierarchies of dominance, but most are. High-status individuals may have great access to resources such as nutrient-rich food items and choice mates. It’s fascinating to consider how monkey and ape individuals come to understand their own relative rank among their groupmates. Televised nature documentaries sometimes give the idea that this understanding emerges from a literal battle: two gorilla males are shown locked in combat, or two monkey females vie for the same limited good.

Research on wild monkeys shows, though, that they are smart enough to learn about dominance by observation – that is, by watching the “social dance” of what other monkeys are doing around them. Japanese macaques (or snow monkeys) make careful choices of alliance partners, for instance, in ways that show how closely they assess others’ social connectedness. When Japanese monkey A is ready to aggress against monkey B, A chooses for an alliance another monkey that is both unrelated to B and higher in status than B.

This example is noted by scientists Paxton, Basile, Adachi, Wilson, Suzuki and Hampton in a new paper published in Journal of Comparative Psychology. Its title is “Rhesus monkeys rapidly learn to select dominant individuals in videos of artificial social interactions between unfamiliar conspecifics.” In it, Paxton et al.also review a captive study in which researchers had tried to understand just how monkeys come to be able to know what they know. In that case, rhesus macaques were shown videotapes of unfamiliar monkeys interacting in real time, in dominance-related contexts.

After first learning how to discriminate dominant individuals early on, the viewer monkeys were able to generalize their learning to novel videos. That is, in experimental trials they reliably picked out the dominant individual on screen.

Paxton et al. believe, however, that those monkeys might have made their choice based on physical markers that correlate with dominance, such as posture, health, and body size. They wondered whether a different type of experiment could avoid that confound, and tell once and for all whether observation of behavior alone is sufficient for dominance learning.

So, Paxton’s team created artificial video tapes and played them for rhesus monkeys. First the researchers filmed individual rhesus macaques each carrying out some activity relating to threats and high-status behaviors. Then, via editing, they paired up monkeys who had not interacted in real time. As the authors note, “This random assignment allowed us to control for any physical cues that might identify a dominant or subordinate individual. The artificial hierarchy was created by showing animal A as the dominant individual in all videos in which it appeared, animal B as the dominant individual when paired with all animals except A, and so on through C, D, and E.”

Next came a twist: The researchers also made what they call identity probe videos. In these, no dominance information was made available. Monkeys (the same ones already used) were filmed eating (or alternatively, jumping) then paired on film; the viewer monkeys could thus only pick out a dominant if they remembered its status from an earlier video.

On both tests the monkeys performed significantly above chance. This result in itself was pretty cool, but scientists being scientists, the team wanted to be sure the monkeys weren’t just memorizing which of the two animals was correct for each pair, instead of generalizing their understanding of dominance. (They worried about this because the monkeys had been reinforced for selecting the dominant animal in early trials).

The researchers decided to present monkeys with videos of two novel individuals interacting with the already-viewed monkeys. In this experiment, no reinforcement was offered. The results allowed the researchers to feel satisfied that the rhesus were not merely memorizing as they went along. However, in the identity-probe trials in this section of the work, the monkeys did less well. They did not make correct choices over multiple trials, suggesting that longer exposure to novel monkeys is needed. To me this finding isn’t a surprise. In real life, rhesus monkeys encounter each other again and again—they don’t glimpse a new individual for only a brief period.

While it is important to seek monkeys’ cognitive limits as well as their successes, I think these ingenious experiments show clearly that monkeys know about others’ relative positions in a hierarchy because they are so well-adapted to acquire social information by observation.

It’s no wonder we humans love to people-watch. Like other primates, we observe closely those around us-- and we draw vital conclusions from what we see.


Comments

  1. November 19, 2010 9:24 AM EST
    Great summary - this study takes the investigation of relative rank (and more) one sophisticated step further than Cheney and Seyfarth with vervet monkeys.
    - Sian Evans
  2. November 19, 2010 9:45 AM EST
    I love reading your postings, Barbara--I think it's fascinating that monkeys watch TV in the same way we do--I'm not sure why it surprises me, but it does.
    - Colleen
  3. November 19, 2010 12:07 PM EST
    Thanks to my loyal readers Sian and Colleen! Colleen, I agree, it *isn't* trivial that other species can watch a two-dimensional screen and come to cognitive judgments of this nature. Two further observations: 1) in very good zoos/ape facilities where I have worked, the apes often have favorite videotapes that they prefer to watch and rewatch, typically those featuring animals. 2) When I was watching the fabulous "Murder of Crows" Nature documentary on PBS, my black cat Pilar was on my lap. She often settles in with me when our family watches TV. However, this time, she was clearly visually riveted to the screen-- watching the crows. (She usually does not visually orient.) I have no idea what she made of the images, versus the crow sounds emitted.
    - Barbara J. King
  4. November 19, 2010 2:51 PM EST
    Thank you for the wonderful review of our paper. I'm glad you found the results interesting and relevant.

    Here is a link to the social cognition page of our lab website. If you scroll to the bottom you can see an example of the edited social interactions we used in this experiment.

    http://www.psychology.emory.edu/lcpc/socialcognition.html
    - -Regina Paxton
  5. November 26, 2010 9:35 AM EST
    My cat Lily is fascinated by a DVD that was given to her when she was a kitten. Called the Cat Sitter Video, it has footage of domestic and wild birds, as well as tropical fish, and caged gerbils, hamsters, mice, etc. But the soundtrack is always bird vocalizations. The DVD is currently available on Amazon, because a houseguest who saw how much Lily enjoyed it ordered one for her cats (ragdolls). One watches, one doesn't. I find that Lily is often motivated to stand up and touch the tv screen if there are animals on it, but she ignores the screen the rest of the time.
    - Melanie Bond

Selected Works

Nonfiction
Why are animals so irresistible to us? Why do we live with and care so deeply about them? From the famous "art caves" of ice-age Europe, to the ancient villages where animals were first domesticated, to stories of apes, whales, dogs, and cats doing fascinating things today, King weaves together a scenario about the animal-human bond that encompasses our past, present and future.
Can scientists discover a prehistory of religion just as they have traced the evolution of technology, language, and art? What does compassion in chimpanzees, or burial patterns in our human ancestors and Neanderthals, tell us about the origins of religion? In Evolving God, named a Top Ten Religion Book for 2007 by the American Library Association, Barbara King explores these questions.
How do chimpanzees, bonobos, and gorillas-- the African apes -- communicate using body postures and gestures? Using her many years of experience studying these apes, Barbara King answers this question in a book that offers a new perspective on the evolution of language.