Shirley C. Strum | Learning from baboons

Shirley C. Strum has spent over 50 years studying wild baboons in Kenya. During that time, she has pioneered new ideas about baboons, about society, about nature, about science and about evolution. As she recounts in her new book Echoes of Our Origins: baboons, humans and nature, she was the first to suggest that baboon society is not based on male aggression and dominance, but that both males and females have effective non-aggressive alternatives. These “social strategies of competition and defence” rely on social relationships that create a “social contract” based on social sophistication, social intelligence, and collaboration, even without the benefits of human characteristics like symbols, language and culture.

Tracking the baboons through ecological and social challenges, Prof Strum uncovered an unknown social complexity as well as documenting the evolution of baboon hunting behaviour, and the development of crop-raiding behaviour. She organised the successful translocation of 3 troops of baboons and documented the social and ecological adaptation of the translocated baboons to a new, harsher environment. Her study of the invasion of an alien cactus species (Opuntia stricta) provides the first ecological evidence for the complexity of the invasion process. Here, we talk to her about her life’s work, and what we can all learn from baboons.

What is the importance of the “baboon model” of primate behaviour to understand our own human evolution?

The baboon model was based on 3 studies done in the 1960’s at a time when we knew very little about (nonhuman) primates in the wild. Because so few primates left the forest which is the main home of primate species, scientists thought that baboons would be a good model for what a puny primate would face in the open. But thanks to Jane Goodall’s chimp study, my baboon study, today’s info on many more species, and sophisticated studies of the biological bases of behaviour, I think that we can’t use any other species as a referential model for humans. That means we shouldn’t use chimps, bonobos, and certainly not dolphins or orcas. Our “human exceptionalism” implicitly seeks to ask “how” other species are different from us because we expect that all species are trying to be us. Human exceptionalism has the implicit assumption that humans are the pinnacle of evolution.

Could you elaborate on why male and female social rank seem to be distinct in most non-human primates?

Male and female social rank is very different in baboons and, as far as I know, in many other primate species. In those other species, it is linked to mammalian reproduction, since females have only a limited range of offspring while males can sire as many young as they are able. For baboons, the species I know best, this difference is present but much more complex for both males and females and eerily dynamic for males as they don’t have a stable dominance hierarchy. The male hierarchy can change every 6 months or less, while the female hierarchy is stable because it is inherited (although some lineages go extinct in my records because I don’t know what happened to the males who migrated out). The function of the female hierarchy is “predictability”, I’ve speculated recently, and not resources that status might bring. Imagine trying to navigate both foraging and social interactions without knowing where you stand. Negotiating your position vis a vis another baboon had to be negotiated at every step. There wouldn’t be enough time for most things and survival would suffer. The female hierarchy is based on reproductive value (Vx) so, within a family, the mother supports her youngest against all other children creating an inverse family hierarchy with the youngest just below the mother. Starting from this simple evolutionary principle, adjacent families get less and less related as the group expands, but the order remains. The female hierarchy I observed in 1972 remained the same even after merging with another troop in 2001 and in 2008. But there are times, like then a matriarch dies, when the whole family might try to improve their rank. It seems to me that the males are free to have a dynamic hierarchy which doesn’t descend into chaos precisely because the females remain so stable and predictable.

Why do you believe hunting did not become a tradition for the baboons in Kenya?

As I watched in my first field study that began in 1972, I saw what I thought was the development of a hunting tradition. Until then, baboons were thought to be opportunistic predators. Baboons’ good eyesight (better than most humans) meant that a young gazelle who froze in tall grass could avoid detection by cat predators, but not by baboons. One day, a particular male left the group and came back covered in blood. After a few times of this, other males followed; soon they were chasing the prey not in a random direction but towards other male baboon “hunters”. Success rate increased. Baboons exceeded chimpanzees, at that time, in the rate of their predation. However, when this male left, he didn’t take his hunting “tradition” to the new group nor did the group he left continue it. It was only when I later observed crop-raiding that I realized the difference. Baboons don’t lack innovations; they lack the ability to make them stick. To do that, the “tradition” has to be observed frequently and in full view of the rest of the group. Hunting didn’t meet these criteria but crop-raiding did. That was why I had to translocate them in 1984 to somewhere that didn’t have any crops or a possibility in the future.

Are crop raiding behaviours by baboons still an issue nowadays?

I couldn’t get my research on crop raiding published in the mid 1980s, but today it plays a growing part in the literature on primates. Human population has expanded which means that there is significant change in land use. For example, more land is needed for agriculture, homes, cities, and suburbs, so crop-raiding has become a problem throughout the world. My study is still the only one which watched naïve baboon groups’ become raiders (or not). Although conflict between humans and wildlife is usually because of human behaviour, it is the animals, like baboons, that pay the price. The incursion of agriculture permanently split the study group into raiders and non-raiders. This changed their diet dramatically so while raiders relied on human food, non-raiders relied on natural foods. And because human foods are large packages of easy to digest nutrition, baboons saved time and energy. They spent more time socializing and resting than non-raiders, so raiders grew faster and larger.

Has their diet changed because of that, or do they now rely heavily on O. stricta?

After translocation in 1984, a prickly pear cactus invaded. As it spread from 2000 until present, Opuntia stricta acted like human food. The cactus fruit was a large package of water, sugars, and micro nutrients that sped up growth and reproduction. But there have been drought periods where fruits don’t grow, so we are currently investigating the impact of prickly pear cactus on metrics of growth and reproduction in females (since males usually migrate out of their “natal” group).

You say at one stage that translocation success relied more on “social” resources and not on competition. Has this been replicated in other translocated populations (of both primates and other animals) when resources are scarce?

I’m not aware of whether other translocations have found this, but this translocation was to a much more arid region where droughts are frequent. Overall, I haven’t observed the type of heightened competition you would expect, under the competition hypothesis. When resources are scarce here like in the end of the dry season, they are very spread out, so there is nothing to compete over. But we are the only baboon project in Africa that monitors the ecology directly. That means I can reliably track the presence or absence of resources based on monthly ecological monitoring. I have found lower than expected competition in all seasons.

Are baboon family and social relationships a good model for human friendship?

As primates and mammals, we share many characteristics. Family is one. Social relationships are another. But I never used the term “friendship” until I was convinced that what baboons do replicates some aspects of human friendship: frequent proximity, lots of socializing, depending on each other. They are the basis of social strategies of competition and defence. Create trust and a relationship first, and enjoy the perks later. So, I think you have it backwards: human friendships convinced me that baboons have friends (with benefits as do human friendships).

How does a primate mind function: are baboons capable of planning and strategy?

I have been troubled for so long by this question: how do you understand a mind that is like ours but still different? My baboon research was part of the shift in the 1980’s which gave back “mind” to primates.  Today we call it cognition. It also has been called intelligence. But as scientists were claiming so many things for humans, I lost interest. Then I discovered “distributed cognition” and “situated action”. These human constructs convinced me that I shouldn’t limit myself to what is inside the head of a baboon. Cognition is also in interactions with other baboons and with the environment, which I can see. By watching baboons, I can interpret behaviours. Baboons are definitely capable of tactics and strategies. For example, agonistic buffering can’t be used to turn off the aggression of another male unless you have an infant that trusts you and only screams at the other male if he persists. This takes some type of planning. At another time, in 2008, the baboons violated all the rules I had come to know about them. They went out of their home range, got mobbed over and over again by the group that lived there, but still came back for more. They lost many animals including all the young infants, and females died of stress (this cause of death was confirmed when we were able to perform autopsies). At the time, there was the invasive cactus in this group’s home range. How did they know? Another troop was trying to fuse with them. However, it was only when the cactus spread to their old home range and they shifted away from the mobbing that their condition improved. The benefits of eating cactus fruit were felt about 8 years later. I don’t think baboons (or humans) can plan 8 years in advance. This changed my ideas about evolution. I had learned from the crop-raiding that baboons have options, they don’t always choose the same thing.  But now I realized that adaptability has more room to operate than we assume because baboons aren’t Descartes’ animal machines.

How do social relationships and fusion/fission of groups evolve in response to predation and availability of food resources? Can this be used to determine social complexity in baboons?

The social group is a compromise between the factors that push baboons together and those that pull them apart. Predation is one of the factors that pushes a group together and conflict is one of the factors that pulls a group apart. There are other benefits of being part of a group and also other costs. I had the opportunity to watch more fissions and fusions than in all the literature on baboons combined. This gave me an idea for rehashing the group concept. For most studies, we just assume the group exists and don’t ask the question why? The rate of change in the Human Age is so fast, that I could watch and interpret events that previously took place over thousands, if not hundreds of thousands of years. That meant that I could see both the role of cactus fruit as food and the role of predation acting together on the group process. These fissions and fusions were made possible because the cactus had spread and there was a lot of fruit. That meant that small groups could find enough to eat (a rare event throughout the seasons without the invasive fruit) but the small groups devised an ingenious method of protecting against predators. Small groups slept near other small groups and a large group, within earshot so to speak, so they had the advantage of many eyes and ears to detect predators. However, in the morning, because social complexity increases with the number of individuals in the group, they simply left to forage in their small group. I think this is the first evidence of selecting a smaller group size to minimize social complexity. But it was only possible because of a dynamic situation which included an abundance of cactus fruit and many sleeping sites.

You say that “Natural history provides a way to put back together the complexity we know exists.” In this context, how do you determine causation for some of the observed events?

Science is reductionist. However, over time, some scientists begin to believe that the phenomena they are watching are simple. Until recently, we did not have the methods to tackle the complexity that anyone who has worked in the field over time knows is there. What puts all the little pieces together from reductionist science? I claim it is “natural history”. It was used by Darwin, but fell out of favour once the study of animals became tests of hypotheses derived from evolutionary theory. I first realized that, (although I was collecting natural history but not calling it that from the start) when thinking about one group of baboons and their response to an encounter with elephants. I noted the encounter and my quantitative data documented the shift in ranging but why did they shift? If I hadn’t written down the elephant encounter, I could entertain many ideas, but I would miss the real one: an encounter with elephants that the baboons, at that time, were afraid of. I’m not arguing that natural history replaces quantitative science. But to understand the reason for changes, to put back the complexity, you need to know more about context. Natural history of events provides the context which may contain the reason for a behavioural shift. Otherwise, how do you link up changes in behaviour, for example, with what caused them?

Could you please comment on how our own human perceptions influence our view of these primates throughout the decades?

We always look to our closest nonhuman primate relatives for the origins of our human behaviour. We “naturalize” this human perspective to give humans biological reasons for why we do some things. When I started in the 1970s, scientists thought that baboons might be a good model for the earliest humans because baboons and humans are the 2 most successful primate species to invade the savanna from the main primate habitat, the forest. Back then, there was even an idea floating around that, although not being primates, social carnivores might be a better model for the earliest humans. Soon, both behaviour and biology of chimpanzees made them a better model. Later, chimps were replaced by pygmy chimps, bonobos, because of additional similarities to us, humans. And today, different scientists prefer specific models, for example chimp warfare and killing has been linked to human warfare. However, after watching baboons for so long, I disagree with any type of “referential” model, whether baboons, chimps, bonobos, social carnivores, dolphins, etc, because we need to look at the “process” by which the behaviours are created, not just the outcome. This helped me see how the unique characteristics of humans (symbols, language, cooperation and culture) changed the nature of human social interactions to help us break the glass ceiling that has prevented baboons from growing their societies.

What is your opinion on how your own identity as a woman researcher influenced the way in which you conducted the research and your focus?

Although I didn’t go to the field with a feminist agenda, I was a second wave feminist who marched in the streets of Berkeley for the right to use the title “Ms”. I’m not certain that I did things differently because I was a woman but I was always fascinated by what didn’t fit. After the baboons didn’t fit the baboon model, I asked why not? I spent most of the next decades trying to figure out what made baboons tick. I started with the males because they were the most dynamically complex, but I always collected information on both large males and females.  I also insisted that others who came to do just males must also collect data on females. I looked at females more closely later and found that they weren’t as simple as they seemed. I did a re-evaluation of what the female hierarchy means. (See above). It is not about status equals resources that matters, but about predictability. The female hierarchy is easily set up with the evolutionary principle of Vx or reproductive value. The transaction costs would be too high if the female hierarchy didn’t order the majority of the group. There are a few situations in which the females can try to change their rank, but these are risky and not often used. Perhaps my fascination with what doesn’t fit, is a women thing. At least my early results that showed female-based families are the core of the group and females did most of the policing and protecting of their kin, not the males, delighted feminists at the time. They used my research to show that women do things differently. I don’t agree. I think it is cultural, which was substantiated in Primate Visions: models of Science, Gender and Society, a Wenner Gren international symposium. Early Japanese primatologists (in the 1950’s to 60’s) were “feminine” in their views and topics although they were all men.

What is the importance of including the participation of local people in baboon conservation and research? Is this the best option for human and nonhuman primates to coexist?

David Western, who started ‘community-based conservation’ in the early 1970’s, says “If people are part of the problem, then people have to be part of the solution.” I took that lesson to heart in 1981 when the study baboons were beginning to raid small farms as the land use changed. I switched from using only grad students to also using local people as research assistants. Local people understand the culture, the problem, and the politics, and can speak the local language. Before the translocation of 3 troops in 1984, the most strident farmer said he would rather have the baboons with the Baboon Project than no baboons at all, because the local people got so many benefits from the Project. Furthermore, having local research assistants, which is now routine in field projects, means they can tell their family and friends about baboons and change hearts and minds. I really think that co-existence is the only way both human and nonhuman primates can live together, but it means that compromise is the operative word. Since we humans have taken so much already, it is our obligation to turn the situation from a win/lose to a win/win. Realistically, it is hard to say this to pastoralists who are barely subsisting. They need options to change their behaviour. Which means that those of us who are wealthy today, must think about how to provide these new options. That is what I have tried to do since I turned to conservation in 1981.

Prof Strum speculates that baboons can’t break a social complexity glass ceiling when they build their society. Still, by tracking baboon social complexity over decades, she observed that the existence of social complexity stops baboon individuals and groups from making simple evolutionary trade-offs of costs and benefits. Furthermore, little twists of fate change the group’s trajectory making adaptation not a tight evolutionary fit between behaviour, society, and ecology; rather, baboons suggest that evolutionary processes have a great deal of tolerance and slippage.