A remembrance of Frans de Waal

Frans de Waal died earlier this month. Widely known for his essays and books, he was one of the world's foremost researchers of nonhuman primates. From the occasions when I was privileged to spend time talking with him, I knew him not just to be a powerful writer but also a powerful thinker. De Waal's work helped both scientists and the public understand the sophistication and flexibility of social behavior in nonhuman primates. He approached all nonhuman animals with empathy and grace.

Many other people have reflected on the impact of his most famous book, Chimpanzee Politics: Power and Sex Among the Apes (affiliate link). First published in 1982, the book described the rich interactions of a group of around 25 captive chimpanzees at the Burger's Zoo in Arnhem, Netherlands. The book recounted episodes within the day-to-day lives of twenty-five chimpanzees, showing what led to aggressive conflicts, highlighting reconciliation, and pointing to moments of deliberate deception. No one could read the book without seeing the calculating minds behind these primates' interactions. De Waal did not think about apes as being like humans; he saw most of human behavior as a special case of ape behavior.

It's not hard to find examples to illustrate de Waal's cultural reach. Here's a good example: the Amazon page for the 2007 reissue of Chimpanzee Politics includes this remarkable quote from Business Week:

“Newt Gingrich has been an avid follower of de Waal's work for years. He has even placed de Waal's Chimpanzee Politics on his recommended reading list, along with better known texts such as the Declaration of Independence, the U.S. Constitution, and the Federalist Papers. What secrets has Gingrich gleaned from our simian cousins? In short, how to win power by forming tactical coalitions and mounting fierce psychological attacks on those blocking the way…It's a strategy Gingrich aped in his assault on former Speaker Jim Wright.”

The study of primate social behavior had come a very long way in the two decades before de Waal began his work at the zoo in Arnhem in the 1970s. Until World War II, ethologists approached nonhuman primates with the idea that behavior was a result of instinct tempered by learning. Psychologists kept captive primates for experiments on operant conditioning, reinforcement, and other simple learning patterns. Studies of wild primates were short, basic surveys of diet and social behavior carried out in expeditions of weeks or months. Such expeditions often ended by shooting the primates that were studied, bringing skins and skulls back to join museum collections.

The groundbreaking work of Kinji Imanishi, who began field studies of Japanese macaques in 1948, began to change what scientists understood about primate behavior. By making careful records of individuals and their interactions, Imanishi and other researchers learned how day-to-day interactions were built from the complex intertwined histories of individuals. That project was followed by others, among the most well-known being Jane Goodall's work with wild chimpanzees at Gombe, Tanzania, Dian Fossey's research on mountain gorillas at Karisoke, Rwanda, and Jeanne and Stuart Altmann's work with baboons at Amboseli, Kenya. Such studies began to reveal how social interactions were shaped not only by mating systems and ecological surroundings, but also personalities, kinship relations, and reputation.

De Waal began his work within a background shaped by these field researchers and their continuing long-term studies. Goodall had found that shifting alliances among the male chimpanzees were central to many interactions within the group. In a convergence of primatology with social science research in humans, such alliances became known as coalitions. By the 1970s, other researchers were documenting the centrality of such coalitions in social groups of other species. Maybe none were as impactful as Sarah Blaffer Hrdy's work with Hanuman langurs in India. She highlighted ways that male and female individuals had competing interests in mating, showing how their interactions, including aggression, coalition-building, and infanticide, were part of wider strategies to meet these competing demands.

From these growing data emerged an understanding that nonhuman primates were in some ways Machiavellian. With his studies of the captive chimpanzee colony at Arnhem, de Waal teased apart some of the influences on their interactions. The captive situation enabled feeding at known times, and at times some individuals might be kept apart, enabling a kind of replication of circumstances that is not usually possible in wild primates. But even more important than de Waal's research results was his ability to translate this emerging scientific understanding for a broader public.

I entered biological anthropology more than a decade after Chimpanzee Politics. By that time many of the book's ideas were already conventional wisdom. I had some great professors who were specialists in primate behavior, but I don't remember any assigning de Waal's book. Everyone knew that primates were strategic in their social behaviors. Meanwhile, the hot areas of research had moved on to questions of mechanisms: how hormones might interact with social behavior, or how DNA studies might enable researchers to look at kinship and paternity influences on behavior.

During the 1990s, de Waal himself shifted into another fascinating area: the study of bonobos. Chimpanzees and bonobos are sister species. Today we know that their common ancestors lived around two million years ago. The Congo River separates all bonobo populations from chimpanzees today, and likely was a barrier from the first separation of the two species. This history was not so clear in the 1990s. Still, it was clear that bonobos are equally close to humans as chimpanzees are. So, de Waal asked, why did so many anthropologists assume that humans had chimpanzee-like ancestors? Why not imagine a bonobo-like ancestor?

Looking at the anatomy of the two species, it might not seem to matter much whether our ancestors were like chimpanzees or bonobos. The body plans of the two species are mostly similar. Even though bonobos were once called “pygmy chimpanzees”, the two species mostly overlap in body size. Both live in communities of 30 to 50 individuals with multiple male and multiple female adults. They knuckle-walk on the ground, climb trees easily and build nests at night, and their communities divide into smaller groups much of the time to find food, the “fission-fusion” organization.

But despite all these similarities, many social behaviors of the two species are starkly different. Chimpanzee groups are shaped by aggressive interactions among males. The male dominance hierarchy, sustained by coalitions that shift over time, determines access to favored foods and mating. Bonobo groups are shaped more by a female dominance hierarchy. Aggression is much more rare, and individuals often resolve potential disagreements with sexual interactions. Sexual contacts between adult females, between females and males, and among male individuals are all common. These basic differences in aggression and affiliation have many consequences across the social lives of each species.

“Because the role of sex in society is such a loaded and controversial issue, scientists have tended to downplay this side of bonobo behavior, whereas the few journalists who have written about the species have naturally hyped it. In this book, I hope to strike a balance: I intend to give the topic the attention it deserves, without reducing bonobos to the lustful satyrs that our closest relations once were considered to be. Sexual encounters of the bonobo kind are strikingly casual, almost more affectionate than erotic. If the apes themselves are so relaxed about it, it seems inappropriate for us to give in to typically human obsessions.”—Frans de Waal

De Waal's consideration of bonobos culminated in his 1997 book, Bonobo: The Forgotten Ape (affiliate link). He dived into the history of scientific study of these primates, and as in Chimpanzee Politics, he included some stories of his own research on the captive bonobos at the San Diego Zoo. De Waal recounted a history that I have told myself in many of my courses; how human evolution researchers once focused on hunting and aggression as roots of human behavior, leading to the idea of early hominins as “killer apes”. While the aggressive interactions of chimpanzees, with their occasional hunts of monkeys and other small mammals, might prompt such a comparison, nothing like this is apparent in the behavior of bonobos. Both species are equally close to humans, so why focus on one and not the other?

As you might well imagine, de Waal took a long interest in human evolution. I first met him at a conference on the topic in 1997, a time when his talks revolved around his bonobo work. He was raising essential questions about what human ancestors may have been like. Even today scientists still haven't resolved many of them.

Researchers did challenge the idea that chimpanzees might provide a model for ecology and social behavior in human ancestors. But the idea of a bonobo model didn't replace it. In part, that is because of new information from fossils and DNA: Fossil species like Ardipithecus or Sahelanthropus lived near to—possibly even before—the last common ancestor of humans, chimpanzees, and bonobos. While these extinct primates seem to have been able climbers, they do not show the kinds of adaptations to knuckle-walking terrestrial movement that chimpanzees, bonobos, and gorillas all share. Some scientists think there was yet another way, a model of locomotion and social behavior that was different from either living chimpanzees and bonobos, and different from later hominins like Australopithecus. Some researchers look more to the ancient past than to the present in understanding these lifeways.

The last time I chatted with Frans was on a visit to his office at Emory University. It was after I had been part of the discovery of Homo naledi, and studying these fossils and their context in the Rising Star cave system had raised many questions for me. I had never before really felt like I was doing work that fell into Frans' area of interest. But now inescapably I found myself asking questions that I had seen before in his books and articles. Many were a big challenge because they had so much to do with behavior, all but invisible from the bones. This species, smaller than most living people with much smaller brains, and some features that suggested more skill in climbing, seemed to have been very much like us in what it ate and how it walked and ran. It had lived in Africa at the same time as some of the earliest members of our own species, Homo sapiens. The extensive finds deep in the cave system suggested that this species had maintained some kind of tradition of cave use, possibly connected with mortuary treatment of dead individuals. What I knew at the time, but wasn't yet published, was that H. naledi skeletons were in several parts of the cave system.

Frans had thought extensively about Homo naledi. He published some of his thinking in a 2015 essay in the New York Times, released on the same day as our first research. With the generic headline, “Who apes whom?” it is easy to miss in an archive unless you deliberately search for it. But it made a big impact on me, and I told him so.

One of my favorite parts of the essay was Frans' comments about interbreeding of hominin lineages. It has always been an important topic in my research, and with genome sequencing the recognition of hybridization and introgression among nonhuman primates has become extremely interesting.

“Did our ancestors, after having split off, keep returning to the apes in the same way that today's grizzlies and polar bears still interbreed occasionally? Instead of looking forward to a glorious future, our lineage may have remained addicted to the hairy embrace of its progenitors. Other scientists, however, keep sex out of it and speak of incomplete lineage separation. Either way, our heritages are closely intertwined.”

The idea of interlinkage of lineages, what today I would call “the braided stream” of human evolution, is important precisely because it confounds the notion of our separation from nature. Not only was there never any point in time that our ancestors suddenly became human, there was never a time that they could have recognized such a distinction from their close relatives.

The main idea of Frans' essay is that humans are not unique. We evolved from primate ancestors who share with us nearly everything once thought to be distinctive. “You name it”, he wrote, “tool use, tool making, culture, food sharing, theory of mind, planning, empathy, inferential reasoning—it has all been observed in wild primates or, better yet, many of these capacities have been demonstrated in carefully controlled experiments.”

He ended his essay with a frank statement of human nonexceptionalism.

“We are trying way too hard to deny that we are modified apes. The discovery of these fossils is a major paleontological breakthrough. Why not seize this moment to overcome our anthropocentrism and recognize the fuzziness of the distinctions within our extended family? We are one rich collection of mosaics, not only genetically and anatomically, but also mentally.”

When I spoke with Frans I told him that I agreed entirely with the conclusion. In fact, my thinking and my conversations with many colleagues were much closer to his than he probably had realized. There is nothing surprising about seeing emotional, cultural, or cognitive overlaps between humans and our extinct hominin relatives. We can be sure of such past overlaps, as Frans pointed out, because we see these overlaps between us and our much more distant relatives, living nonhuman primates.

Most scientists readily accept the high degree of morphological and genetic continuity that connects us with ancient hominins. Yet many still resist the idea of mental continuity. They imagine a time that ancient humans suddenly transformed to “behavioral modernity”. According to this concept many behaviors and ways of thinking that humans share had emerged all together as a package: language, symbol recognition, creation of ornaments, use of pigments, and complex toolkits. This combination, the story goes, enabled our species to displace other hominins and ultimately drive them to extinction.

De Waal was not an archaeologist, although he embraced the growing complexity of the archaeological and fossil record. He regarded the assumption of human uniqueness as a conceptual error, which he perceived to be shared by many archaeologists and paleontologists. Ancestral hominins occupied the space between ape and human. If humans are more apelike than we usually admit, and apes more humanlike, then the space between apes and humans may be quite a lot smaller, easier for evolution to bridge. I think of one of the opening passages of Bonobo, which conveys the essential commonality between us and our close nonhuman relatives.

“When the lively, penetrating eyes lock with ours and challenge us to reveal who we are, we know right away that we are not looking at a ‘mere’ animal, but at a creature of considerable intellect with a secure sense of its place in the world. We are meeting a member of the same tailless, flat-chasted, long-armed primate family to which we ourselves and only a handful of other species belong. We feel the age-old connection before we can stop to think, as people are wont to do, how different we are.”

Notes: In his subsequent books, de Waal highlighted many more pathways by which the behavior of nonhuman primates and other animals help to illuminate familiar human behaviors. He discussed the occurrence of traditions, behaviors shared across generations, which are fundamental to human cultures and which ethologists increasingly recognize within nonhuman species.

All of his books reflect a broad engagement with culture and politics outside of academic research. In one recent book, Different: Gender Through the Eyes of a Primatologist (affiliate link), de Waal discussed how sex and gender identity in humans has a broader context in the study of other species.

My personal favorite of his books, which I have often assigned in courses, is The Ape and the Sushi Master: Cultural Reflections Of A Primatologist (affiliate link). Published in 2001, it was one of the first popular books to present the emerging science of cultures in nonhuman primates. The stories from the history of primatology that he shares in this book are part of the essential canon of primate behavioral ecology.

References

de Waal, F. B. M. (2015). Who Apes Whom? New York Times, September 15, 2015, A23.

de Waal, F. B. M. (2022). Different: Gender Through the Eyes of a Primatologist. W. W. Norton & Company.

de Waal, F. B. M. (2007). Chimpanzee Politics: Power and Sex Among Apes. JHU Press.

de Waal, F. B. M., & Lanting, F. (1997). Bonobo: The Forgotten Ape. University of California Press.

de Waal, F. B. M. (2008). The Ape And The Sushi Master: Cultural Reflections Of A Primatologist. Basic Books.