Humans aren't the only species who learn by aping their elders
By Bruce Lieberman
San Diego UNION-TRIBUNE STAFF WRITER
November 9, 2006
It is such a basic part of human nature that we don't think twice about it: Adults pass their habits, knowledge, traditions and skills on to the young.
JOHN GASTALDO / Union-Tribune
At the San Diego Zoo, a bonobo mother and child spend time together.
That relationship gives rise to a dizzying array of cultures – defined by the way people dress, eat, marry, die, believe in a deity or not and on and on.
For millenniums, people have believed that culture and intelligence define what being human is all about. Now science has advanced that view, finding compelling examples for culture in the animal world.
Songbirds teach their young their signature melodies, each with distinct dialects unique to their geographic location.
Killer, pilot and sperm whales pass on to their kin knowledge about feeding and defending against predators.
Some dolphins attach a marine sponge to their snouts, as a foraging tool and possibly for protection, as they prod the sandy sea floor for hidden fish. Mothers pass this behavior on to their children.
In terms of culture, no animals have been studied as extensively as nonhuman primates – chimpanzees, gorillas, orangutans and bonobos. Studying cultural traits in these creatures ultimately will provide clues to human evolution and the development of culture and society in our species.
“Defining humans is basically a comparative exercise,” said primatologist Carel van Schaik, author of “Among Orangutans: Red Apes and the Rise of Human Culture.” “The only way to find out who we really are is to compare us with all our living relatives.”
JOHN GASTALDO / Union-Tribune
A bonobo pulls a stick from an artificial termite mound, a behavior adults teach their children.
Trying to understand culture in great apes has been confused by the difference between their behavior in captivity and in the wild. Gorillas, orangutans and bonobos are social and intelligent in captivity, but seem unsocial and technologically challenged in the wild.
Van Schaik, director of the Anthropological Institute and Museum at the University of Zurich, has called this a contrast between “zoo genius and forest bumpkin.”
Over the past few decades, however, primatologists have begun to solve this puzzle. First, it's clear that captive great apes, freed from the pressures of life in the wild, have more time for the social interactions that promote learning from one another. Perhaps more importantly, primatologists, now looking longer and more carefully at great apes in the wild, have found more examples of intelligence and distinct cultural behaviors.
A succession of studies has revealed that the private, wild lives of great apes are much more complex than most scientists ever imagined. Not only are these animals intelligent and innovative, but they routinely pass on acquired knowledge to their children. That knowledge varies from one group to the next, depending on geography – a hallmark of culture.
Stick tricks
One of the first scientists to define culture was Kinji Imanishi, considered the father of Japanese primatology, who in 1952 described culture as socially transmitted innovation.
A young orangutan, for example, will learn from its mother how to use a stick to scoop honey from a tree, or extract seeds from a husk – and pass that behavior on to its own young.
“If you grow up alone,” said van Schaik, “culture is what you never get.”
In 1999, a groundbreaking study in Central Africa documented 39 behaviors – from tool use to grooming to courtship – that were habitual in some chimpanzee communities but absent in others. Ecological differences – say, the terrain or vegetation of a place – could not explain these variations. Previously, only single behavioral patterns, such as differences in the local dialects of songbirds, had been identified.
In their study, Andrew Whiten, Jane Goodall, Christof Boesch and their colleagues cataloged variations in behavior among chimp groups from Guinea, Ivory Coast, Uganda and Tanzania.
BETHAN MORGAN / Zoological Society of San Diego
Quartz fragments and cracked Coula fruits are used by chimpanzees in the Ebo forest of Cameroon.
Customary behavior among chimps in the TaïForest in Ivory Coast, for example, included cracking open nuts by smashing them on a stone surface with a heavy stick. But chimps in Bossou, Guinea, to the north, didn't display the behavior.
In Gombe, Tanzania, chimps used sticks as levers – to enlarge the entrance of a hole, for example. Chimps in Mahale, Tanzania, showed no such behavior.
In Budongo, Uganda, chimps used leafy sticks to fan flies. Their neighbors in Kibale, Uganda, didn't do it.
Newer studies have added more wrinkles to the cultural lives of chimps.
An isolated population of a subspecies of chimpanzee in the central African nation of Cameroon crack open hard-shelled nuts using stone or wood as a makeshift anvil and a quartz stone as a hammer. The technique had previously been seen only in the Ivory Coast – hundreds of miles away.
BETHAN MORGAN / Zoological Society of San Diego
In Cameroon, a rare subspecies of chimpanzee cracks open hard-shelled nuts using a stone or wood “anvil” and a quartz stone as a hammer.
This suggests chimps may have invented the same technique numerous times, each time passing the behavior on to their young, said Bethan Morgan, a researcher with the Center for Reproduction of Endangered Species, part of the Zoological Society of San Diego.
“It's very difficult to say what's going on, because nobody's really studying chimpanzees in any of these areas to any extent,” said Morgan, who published the study in the journal Current Biology.
At the YerkesNational PrimateResearchCenter in Atlanta, captive chimpanzees clearly demonstrate their talent for learning from one another.
In a study published in Nature in 2005, Whiten, Frans de Waal and primatologist Victoria Horner taught a female chimp one way to open a box, and another a different way. Each animal then taught compatriots in its group to open the box in the distinct style it had been taught.
Subsequently, the primatologists, in research published in September in the Proceedings of the National Academies of Science, taught a chimp a particular technique to open a box. The chimp then taught a second chimp, who in turn taught a third, acting like links in a chain.
Some scientists have long thought that only humans had the capacity to imitate – that is, learn from others around them.
“Part of the reason for us to do these experiments was to show that that's really not true,” said de Waal. “Chimpanzees are really great imitators, which is what you'd expect if the variation in the field has anything to do with social learning.”
Gorilla technique
Many primatologists suspect that the other great apes – orangutans, bonobos and gorillas – also rely on social learning in the wild, and are in some cases skilled tool users.
In 1993, van Schaik discovered a population of wild orangutans deep in the swamp forests of Aceh in northern Sumatra. The density of orangutans was more than 10 animals per square kilometer – “through the roof,” he said.
Over six years, the orangutans' adept use of tools for foraging, tree nest building, tightknit family groups and propensity for social learning were documented.
The orangutans proved multitalented with tools, using sticks to hunt for termites, ants and honey. Some sticks were used to delicately probe the honeycombs of stingless bees, while others were used to hammer chunks off termite mounds.
The orangutans also used short sticks to extract seeds from their hard, woody capsules surrounded by razor-sharp needles that hang from Nessia trees. The orangutans fashion twigs to detach the seeds without getting hurt.
“They're on a par with chimps, and that shouldn't be a surprise,” van Schaik said. “In captivity, it's the orangutans that are known as the great tool users, not the chimps.”
De Waal suspects that the bonobo may be just as talented.
In captivity, bonobos clearly learn from one another. At the San Diego Zoo, 2-year-old Kesi rides on the back of her 27-year-old mother, Lana. The youngster watches attentively as Lana probes a cement “termite mound” with a stick to extract peach baby food placed by zookeepers. Adult bonobos chew one end of their sticks, fraying it into a crude brush that can soak up more food. Despite their talents in captivity, bonobos in the wild display few tool-use skills – at least as far as researchers have seen.
“Everyone is very puzzled by it because they're so closely related to the chimpanzee that uses a lot of tools,” de Waal said. Eventually this is likely to change, he said, as primatologists make further observations.
Gorillas appear less skilled at using tools than chimps, orangutans or bonobos. But researchers have observed a wild gorilla using a stick to check the depth of a river. And at the San Diego Zoo, Japanese researcher Masayuki Nakamichi has documented gorillas using sticks to knock leaves out of trees.
For other tasks, gorillas have their own method. When challenged to open a box, one gorilla banged it on the ground. It worked.
“That's a typical gorilla way,” de Waal said. “The gorilla is so incredibly strong that he can crack any nut; he doesn't need stone tools for that. He puts them between his teeth and they're gone. Why would you develop stone nut cracking if you could do that?”
Challenges to further study
Such revelations about intelligence and social learning have led van Schaik to propose that culture is probably a precondition for advanced intelligence. After all, human advancement stands on the shoulders of previous generations – and that ever-growing pyramid of knowledge is built on social learning.
“Where those opportunities are abundant, you get smarter adults, and over evolutionary time, that means you create opportunities for selection,” van Schaik said. “The efficiency of learning goes up, and therefore the investment of brain tissue gives you greater returns.”
So, why has intelligence advanced so far in humans and not in other social animals that display features of culture – such as dolphins, elephants and great apes?
“In theory, there could be plenty of other species in which this happened, except that the process stops at some point,” van Schaik said “There's an equilibrium (between the benefits of social learning and brain capacity) that gets reached.”
As scientists have learned more about great apes, they've developed a great respect for the animals.
“When you study a monkey, you can pretend a little bit more that you're not really looking at our ancestry,” van Schaik said. “But once you switch to apes, there's just no way around that fact. There's no way back.”
Many primatologists find it unconscionable that great apes would be used routinely for medical research, and van Schaik echoed that view.
“As a field worker, you spend thousands of hours observing every detail of their lives, and you can't help but be impressed with almost everything you see. The similarities (to humans) are a lot greater than the differences.”
More field studies are needed to better understand culture in primate societies. But great apes are difficult to observe in the wild, whether in the steamy, dense jungles of Sumatra, the high mountains of Cameroon or the wilds of the CongoBasin.
Sadly, great apes are under siege. In Southeast Asia, logging is robbing the orangutan of its habitat. In Central Africa, chimpanzees, gorillas and bonobos are falling victim to an aggressive bush meat trade.
These pressures threaten to unravel complicated primate societies that scientists are only now beginning to understand.
“Look, after we know all this, we can't just sit and watch how their habitat is destroyed for no good reason,” van Schaik said. “These animals are going extinct, and we cannot let them go quietly.”