Black-and-white ruffed lemurs can learn to do complex tasks simply by watching a fellow member of their troop.
When researchers showed one lemur how to manipulate a simple snack machine, all other lemurs in its troop successfully performed the same trick on their first try. That lemurs can learn socially like their distant primate relatives, including apes and humans, suggests they possess an underpinning to human-like culture.
“We don’t really understand how culture evolved,” said primatologist Tara Stoinski of Zoo Atlanta, co-author of the upcoming study in Biology Letters. “To do that, we need to look more broadly at primates and include lemurs in cognition research.”
Lemurs’ only natural habitat is isolated on the southern tip of Madagascar, a large island off the southeast African coast. They are members of a small group of primates called prosimians, which split off the evolutionary tree about 63 million years ago from simians, a grouping of primates that includes gorillas, chimpanzees, Old World monkeys and humans.
Most cognitive research has zeroed in on simian animals and found them to be highly adept in social learning, tool use and other essentials of human-like culture. Lemurs have been mostly excluded because studies in the 1960s suggested they weren’t very bright.
“Recently, however, we’ve seen tool use in lemurs, and recognition of tool features,” said psychologist Laurie Santos of Yale University, who studies primate cognition but wasn’t involved in Stoinski’s research. “For the most part, researchers just really haven’t looked.”
To test prosimian social learning abilities, Stoinski and her team built a snack-filled tube with two different ways to open it -- a hinged door and a sliding door. They trained one lemur to open the hinged door, then had four lemurs watch their comrade repeatedly open it and get snacks inside. They trained the same lemur to use the sliding door to get snacks and exposed four different lemurs to that scene.
Both groups of lemurs emulated the trained animal on their first encounter with the snack-filled tube, and continued to use the same door even though another one existed. One group eventually figured out how to open the other door (by accident), but even so Stoinski said the experiment was one of the first controlled demonstrations of social learning in lemurs.
“This is a means of learning we take for granted as humans,” Stoinski said. “We can’t say this instance is culture -- it's nothing like the equivalent of learning a geisha tea ceremony. But it’s what allows for transmittance of cultural norms.”
If more evidence piles up in favor of prosimian social learning, it’s almost a given that the ability first emerged before prosimian and simian primates split about 63 million years ago, Santos said. “It’s the simpler explanation. The more research we do on more distant species of primates, the better window we have to their common ancestor."
In the future, Stoinski would like to try more advanced tests of cognition. Though zoos are good places to perform the research, more studies of lemur troops in the wild would be nice, she said. But that's becoming more difficult as the primates lose their natural habitats.
“Before we can understand how rich of a society lemurs may be capable of, we may lose wild populations,” Stoinski said. “If that happens, we lose the ability to answer a lot of questions about how culture emerged.”
Images: 1) A baby black and white ruffed lemur. Credit: Zoo Atlanta/Tara Stoinski. 2) A lemur manipulates the device used in the two-action experiment. Credit: Zoo Atlanta/Tara Stoinski. 3) Ring-tailed lemurs sleep in a wildlife park. Credit: Flickr/Daves Portfolio
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