Clemson scientist shares story of discovering learning behaviors in non-human primates
GREENVILLE — Monkey see, monkey do – but what if the monkey could be taught, rather than thrust into observation?
Clemson behavioral ecologist Lisa Rapaport recently talked about her research on the foraging habits of a small New World monkey called a golden lion tamarin in a packed room at Coffee Underground in downtown Greenville. Rapaport’s presentation was at Science on Tap, a community forum for scientific discussion hosted by professor Victoria Corbin of Clemson University’s Life Sciences Outreach Center.
For humans, the transfer of skills is necessary for our survival. As children, our parents acquire, prepare and feed us our food until we’ve become cognizant enough to do it ourselves. Even without the amenities of first-world living, modern human hunter-gatherers will provide food for their offspring and show them how to skillfully hunt on their own.
“We don’t think of these as being very special behaviors because we, humans, do them all the time,” said Rapaport, an assistant professor in the College of Science’s department of biological sciences. “But the interesting thing is, when we look at other animals to see if we can find these behaviors in simpler form, to try and understand how these developed during human history, we find that the rest of the primates rarely give food to their weaned kids.”
For example, young baboons will watch their mothers’ actions to understand where and how to get food, but mother baboons don’t actively help their infants in this pursuit. Even chimpanzees, which share 99 percent of human DNA, leave infants to fend for themselves when it comes to foraging.
It was thought that social learning – gaining knowledge solely through observation – was the law of the land for nonhuman primates, until Rapaport’s study on the foraging behaviors of golden lion tamarins.
“Like we see in human hunter-gatherers, and even among our own families, all adults in a tamarin family give food to kids,” Rapaport said. “In fact, infants receive over 90 percent of their solid food from group members. It’s not like these other monkeys or chimpanzees, where the kids scrounge for the leftovers; the foods that are given to young tamarins are those that are the most difficult to acquire, the most highly preferred and the ones with the highest nutritional value. The adults in this system really do help kids learn about food.”
By providing food to their young, adult tamarins are teaching their kids how to find nutritious, healthy foods among the wealth of options – some of which are toxic – that exist in the Atlantic coastal forest of Brazil.
“The tamarin diet is very complex,” Rapaport said. “During my time in Brazil, I recorded at least 150 different species of plants that they ate, including fruits that range from really large to really tiny, which all mature at different times of the year. But tamarins also eat prey consisting of everything from lizards to frogs to insects and spiders that live in nasty little crevices and holes.”
For an animal that is weaned just three months after birth, how does a young tamarin begin to know where and how to forage?
The answer relies on an adult tamarin being nearby and eager to help infants as they navigate the food-getting process.
Unlike other primate species, adult tamarins aren’t bothered when their young co-forage in the same spot. When they see their infants struggling to acquire food, they will intervene and provide assistance. For instance, if a young tamarin is wrestling to pull a fruit from its stalk, the adult will intercept the stalk and pull the fruit for the kid. In other instances, if an adult comes upon a type of food that is coveted – typically small animal prey – it will make a distinct food offering call that alerts the kid to the find.
“What I think is, adults are doing these things to motivate their kids. It also might inform kids that this is a good place to look – this is where you should go to find a hidden grasshopper,” Rapaport said. “Another one of my ideas is that some of us learn quickly, but some of us don’t. So maybe adults are only using these behaviors for their slow learners to get them up and going.”
Rapaport says that if humans want to learn more about our cooperative, empathetic, caring nature, we should look to the golden lion tamarin – whose behaviors mimic our own – before considering our more closely related ape relatives.
“The more difficult your foraging behavior becomes – like hunting, or like digging up food before you can see what it is – the more that requires you take care of kids and feed them,” Rapaport said. “But in nonhuman apes, only mothers care for their young. There’s no paternal care. There are really no caregivers to help with the kids. Yet, all tamarins live in cooperative family groups. When the young are grown, they oftentimes stay in their family group for varying amounts of time, sometimes as much as a couple of years, and they help to care for their younger siblings. And adults really go out of their way to help their young learn the really difficult foraging activities. It’s a family affair.”
Despite their value as a window into human evolution, golden lion tamarins are an endangered species whose home is being leveled to cater to the growing tourist population in Brazil. Ninety-three percent of the Atlantic coastal forest has been decimated, leaving only about 2,000 tamarins in the wild. Poço das Antas and União – two biological reserves located in Rio de Janeiro – are leading conservation efforts to protect the golden lion tamarin population by reintroducing captive tamarins to the wild or relocating them from fragmented forest areas.