Studying the social knowledge of a troop of baboons in Botswana, Penn researchers Dorothy Cheney and Robert Seyfarth gain insights into monkey cognition—and our own.
By Susan Frith | Illustration by Noah Woods
Consider the plight of a certain high-ranking hominid who moves into a new habitat, a place we’ll call Netherfield Park. After some social contact with the eldest of the neighboring female offspring, he has a strong urge to mate. But his own sisters interfere because of her “low connections” and “vulgar relations.”
The male hominid goes by the name of Mr. Bingley; the female, Miss Jane Bennet. Both inhabit the special preserve of one Jane Austen. As Pride and Prejudice illustrates, Homo sapiens carry a keen sense of who’s related to whom, and how others stack up in the social rankings. It turns out we aren’t the only ones.
According to two Penn primatologists, Dr. Robert Seyfarth and Dr. Dorothy Cheney, baboons appear to do the same—a finding that may shed light on theories about the evolution of human cognition and language.
Cheney, professor of biology, and Seyfarth, professor of psychology, have spent more than 25 years studying the communication, cognition, and social behavior of non-human primates, including vervet monkeys in Kenya and baboons in Botswana. Their work, including the 1990 book How Monkeys See the World, has illuminated similarities and differences between humans and some of their closest relatives.
“The basic premise that we start off with,” says Seyfarth, “is that you can’t understand an animal’s brain and how it works without understanding the society in which that brain lives.”
That brings Cheney and him to the Moremi Game Reserve in the Okavango Delta. The three-square-mile swath of woodland and savannah is home to a formidable mix of lions, leopards, hyenas, and elephants, along with a troop of about 80 baboons. With the aid of binoculars, hand-held computers, recording devices, and vials of poop preservative (for hormone testing), Cheney, Seyfarth, and their assistants methodically track the movements of the Papio hamadryas ursinus. Following the baboons at a distance of about six feet, they avoid eye contact and interact with their subjects as little as possible.
Baboons are the long-snouted bullies of the savannah, with the bigger male growing to about the size of a Labrador retriever. They aren’t afraid of much, Seyfarth says. “And what they are afraid of—with the exception of lions—their attitude is, ‘Let’s fight it.’”
They dine on fruit from the local mangosteen trees, wild figs, rodents, and vervets. Access to prime feeding spots goes to the highest-ranking individuals—and every baboon appears to know who they are.
“If you look at a group of baboons, you’ll see females arranged in a dominance hierarchy,” says Cheney during an interview with both researchers in her Leidy Laboratories office. They maintain close bonds with their kin. The females assume ranks just under their mother in inverse relation to their birth order, and an entire family tends to be above or below the next. “You’ve really got a kind of hierarchy of families—like in a Jane Austen novel.”
It’s 9:30 a.m. on the game reserve. A member of Family A chases and bites a member of Family B. Fifteen minutes later, a member of Family B looks over and threatens a member of Family A.
The question Cheney and Seyfarth have tried to answer is how much the animals themselves understand the complex system in which they’re participating: “It looks like these monkeys are very, very good at this,” Cheney says. The baboons’ videotaped reactions to simulated fights show that they recognize not only their own place in the social network, but the ranks and relationships of others in their group. Furthermore, they recognize that not all social interactions carry the same weight.
Feuds between families—think of the Montagues and Capulets—are a bigger deal than feuds within families. A rank reversal between two sisters will only affect rank relationships within the family, but if two members of different families reverse rank, it will cause two entire matrilines (female kin groups) to follow suit.
In the November 14 edition of Science, Cheney and Seyfarth—with post-doctoral researchers Thore Bergman and Jacinta Beehner—published results of a study in which they recorded vocalizations of 19 adult female baboons and played them back in different sequences over a hidden loudspeaker.
When individual baboons heard a vocal exchange between two others that was consistent within the existing hierarchy (such as the more dominant animal B threatening C), they looked toward the sound briefly—about 1.4 seconds on average—and then went about their business. The average looking time increased to 2 seconds, however, when exchanges that appeared to go against rank within a family took place (C threatening B). It increased to 4.2 seconds in reaction to a “rank reversal” between baboons of two different families.
Upheavals among female baboons are rare, and higher-ranking families generally support the status quo, Seyfarth says. “It’s very Jane Austen.”
“If the whole hierarchy is upset, it could upset you, too,” Cheney points out.
Female rank has nothing to do with size or age and everything to do with who your allies are. Though rank order among baboon matrilines can remain stable for several generations or more, families can lose dominance when they lose members. (Male baboons, which leave home as adults and are dominant to all the females, play by a different set of rules, in which chutzpah, fighting ability, and big teeth come in handy.)
Baboons split from the common ancestors of humans and apes about 35 to 40 million years ago, so they are not nearly as closely related to people as chimpanzees are. (But apes are harder to study in their natural habitats, which are in politically less stable countries.) Like other monkeys baboons don’t use tools and they don’t show the kind of cultural behavior seen in chimpanzees. And yet they appear to have a sophisticated social knowledge.
To give one example, a low-ranking female baboon interested in upward mobility might go about it by becoming “very close buddies” with a higher-ranking baboon—perhaps by picking ectoparasites from her coat or forming an alliance with her during a fight.
There is some anecdotal evidence that “if you’re a very low-ranking female, you do better if you don’t have any relatives,” Cheney says. “You can freelance. You can establish a very close bond, particularly if you’re young, with a middle- or high-ranking family.”
When one observes such tactics, says Seyfarth, “That leads you to say, maybe these are the kinds of social pressures that cause primates to have big brains. They’ve got to know a lot of stuff in order to pursue the best social strategy.”
And the pressures to sort matters of rank and kinship in a complex society may have favored the evolution of humans’ ability to sort words and make meaning out of sentences.
The grunts, wahoos, and barks of baboons are part of the background music of the game reserve. Sometimes they signal a squabble: a threat-grunt rumbles forth from one baboon, followed by a submissive scream from another that sounds to the untrained ear like a parrot being squashed. Depending on how you divide it up, baboon communication consists of six or 40 distinct calls.
This puts baboons in a similar category with mollusks, which communicate with 15 to 35 “qualitatively distinct, significant displays,” according to Dr. Mark Liberman, professor of linguistics and director of Penn’s Institute for Research in Cognitive Science.
“It doesn’t mean monkeys aren’t a whole lot more complicated or smarter than squid, but in this dimension, there doesn’t seem to have been a lot of [evolutionary] change,” he says. “One of several puzzles about language is what happened a while ago, whenever it was—two and a half million years or 200,000—to push us off in this direction that leads us to having 60,000 different signs or more.”
One challenge in understanding the higher cognitive abilities of humans, especially language, Liberman adds, is that “we don’t have very clear animal models for them” like we do with visual perception or hand-eye coordination. “So whatever comparisons we can come up with through the work of people like Seyfarth and Cheney are all the more precious, I think.”
Both collaborators and spouses, Seyfarth and Cheney met in college. Later they became graduate students in zoology at Cambridge, working with Robert Hinde, a leading figure in animal behavior and supervisor to Jane Goodall. They came to Penn in 1986 after working at Rockefeller University and UCLA.
Liberman calls their work on “how animals communicate with each other and we might communicate with them … the most clear-headed and careful and systematic and well controlled and insightful that is around,” adding that, “They’ve also taught and influenced many of the people doing good work in that field.”
One problem in solving the language puzzle, notes Seyfarth, is that there are no primitive languages—in other words, languages that can be seen as simpler than another. “If you wanted to explain the evolution of bipedalism, paleontologists could take you to some bones and say this is why this creature was on its way to becoming bipedal, but it was not there yet,” he says. “It’s much harder to look to a system of communication in animals or language in humans and say this is on its way to becoming language, but it isn’t there yet.”
Some insights have come from studies of children’s language-learning, which show that “such learning does not emerge completely on its own but instead begins with the child’s understanding of objects and events in the world,” Seyfarth and Cheney write in an email. “Before the child has words, she has a kind of conceptual structure.” Dr. Lila Gleitman, Dr. Henry Gleitman, and Dr. Elizabeth Shipley, all psychologists at Penn, showed many years ago that “children comprehend complex sentences long before they can produce them, and that children are aware of grammatical errors long before such knowledge appears in their own speech.” (Even dogs—which don’t produce linguistic communication—seem to understand it in some way when it is used by humans, Seyfarth and Cheney point out. And, as their own work shows, baboons have a small vocal repertoire compared to humans, but, “They seem to understand a great deal about their environment.”)
“As with the development of language in children, people generally believe that language evolved from a rich cognitive structure in our pre-linguistic ancestors,” Cheney and Seyfarth write. Their own work proposes that the roots of language lie in “our structured hierarchical knowledge of social relationships.”
According to Liberman, a number of theories focus on social relations, including the ideas that language emerged out of the need to “make what were in effect marriage vows”—public promises “basically [about] male food provisioning in return for female sexual fidelity”—or to “provide pleasant social bonding via gossip.”
“It’s very clear that primates are extremely social animals [with] complicated social networks and social hierarchies based on genetic relationships and alliances—who was nice to whom, who was mean to whom in the past,” Liberman says. “So it’s very important to primates to keep track of those structures and reason about them—and perhaps to communicate about them.”
Cheney and Seyfarth’s work is “interesting not only in that it suggests that social organizations might have been one of the kinds of structures that linguistic forms nucleated around, but it also connects these other ideas with what it was that motivated our ancestors to develop language in the first place.”
A group of baboons spreads out in a wooded area. From the sounds they make, it seems like they’re exchanging “contact barks” with one another. But the purpose isn’t to inform separated individuals of the group’s whereabouts. Individuals simply make the sounds when they are alone or on the periphery, according to Cheney and Seyfarth.
One key difference between humans and non-human primates that is explored in their research is “theory of mind”: Humans have it; monkeys and apes don’t. Identified in the late 1970s by then-Penn psychologists David Premack and Guy Woodruff Gr’77, “theory of mind” is an ability to attribute mental states to others and take them into consideration during one’s communications. Humans aren’t born with this ability but learn it through experience.
To give an example, if you show a three-year-old a box of candy and ask what’s inside, the child will guess “candy.” If you then show the child that the box actually contains matches and ask him what his friend Freddy will say is inside the box, the three-year-old will say “matches.” That’s because before age five or six children don’t recognize the difference between what they and others know.
Monkeys and apes don’t try to inform those who are ignorant or instruct their offspring that something is dangerous for them. Seyfarth and Cheney have found that while baboon vocalizations “often function to alter the behavior of listeners, there is no evidence that callers take into account their audience’s mental state.” Similarly, they write, “listeners’ responses seem governed primarily by learned behavioral contingencies rather than any appreciation of signalers’ motives or beliefs.”
Their interest in the relationship between the natural communication of primates and human language contrasts sharply with well-publicized studies in which chimpanzees or gorillas have been brought to the lab and “taught” a form of human language. Though research in captivity can yield valuable information that is difficult or impossible to obtain in the wild, “you run the risk that your results will give a false picture of the animals’ behavior under natural conditions,” Cheney and Seyfarth write. They prefer to study how primates communicate on their own terms in their natural habitats.
Most researchers who come to the Moremi Game Reserve to study baboons need at least six weeks to tell the individual animals apart from one another. As Cheney describes it, it’s a time of “unrelieved tedium and desperation, boredom, and frustration,” relieved only by the beautiful scenery and the occasional threat of being charged by wild buffaloes. (The key is “to spot them before they spot you,” Seyfarth says, then to move out of the area as quickly as possible.)
Gradually, as one gets to know all the baboons, they become like characters in an “incredible soap opera,” Seyfarth says.
Episode 1: Sierra, who’s much higher ranking, goes over to handle Hannah’s baby. Hannah threatens Sierra, and as a result, Sierra backs off. An hour later Sierra approaches Hannah again. Hannah acts nervous. She’s done something she shouldn’t have. But she lets her guard down when Sierra grunts and smacks her lips in the way that baboons do to show benign intent. Suddenly Sierra jumps on Hannah and bites her.
Jane Austen’s characters don’t go that far, but like most interesting dramas, this one leaves room for interpretation. “On the one hand you could say Sierra has been sitting here fuming for the last hour because she was threatened when she shouldn’t have been,” and she fakes being nice to Hannah to get even, Cheney says. “On the other hand, it could also be that Sierra is like, ‘Oh I want to go be near Hannah, Hannah has a baby. Oh, wait a minute. I seem to remember I’m angry at her.’ Which is less complex.” Perhaps later episodes with a larger cast of characters will offer more clues.
Actual fights among adults are pretty rare in the day-to-day existence of baboons, which is often spent finding food and avoiding predators. But there is plenty of material to keep the researchers occupied. “We can go out for a day of watching with one of our post-docs—and if you were with us, you wouldn’t be hearing any screaming or shouting,” Seyfarth says. “You wouldn’t see any rage of nature, tooth and claw. But on the way back, your post-doc would turn to you and say, ‘Do you detect a seething tension between this family and another?’ And you’d say, ‘Absolutely.’”
This summer Seyfarth and Cheney will return to the field to continue their research on the role that hormones and personality may play in the social hierarchy of baboons. Hormones associated with stress may account for certain personality differences; one unglamorous but noninvasive way to find out is collecting and testing baboons’ fecal samples. (The Bingley sisters would be most appalled.)
“There are alpha females and there are alpha females,” Seyfarth says. Some of the top-ranking females are “really insecure—very aggressive, gratuitously nasty.” (Think of Mr. Bingley’s sisters ridiculing Eliza Bennet’s wild hair and muddy petticoat.) “There are other females that are sort of the grand dames, dispensing friendly gestures throughout the group.”
In addition, Cheney says, “there are some low-ranking females everyone seems to like even though they are low ranking.” That would explain the social rise of Jane and Eliza Bennet.
But that’s another story.