Captive apes under enlightened conditions (such as a sizable group in a spacious outdoor area) have the added advantage of providing a close-up look at naturalistic behavior that one can’t get in the field. Here apes can be watched and videotaped much more fully than is possible in the forest, where primates often disappear into the undergrowth or canopy as soon as things get interesting. Fieldworkers are often left to reconstruct events based on fragmented observations. To do so is an art, and they are very good at it, but it falls short of the behavioral detail routinely collected in captivity. If one studies facial expressions, for example, zoomed-in high-definition videos that can be slowed down are essential, which require well-lit conditions rarely encountered in the field.
No wonder the study of social behavior and cognition has fostered integration between captive and fieldwork. The two represent different pieces of the same puzzle. Ideally, we use evidence from both sources to support cognitive theories. Observations in the field have often inspired experiments in the lab. Conversely, observations in captivity—such as the discovery that chimpanzees reconcile after fights—have stimulated observations in the field on the same phenomenon. If, on the other hand, experimental outcomes clash with what is known about a species’s behavior in the wild, it may be time to try a new approach.11
With regard to the question of animal culture, in particular, captive and fieldwork are now often combined. Naturalists document geographic variation in the behavior of a given species, suggesting a local origin and transmission. But they often cannot rule out alternative accounts (such as genetic variation between populations), which is why we need experiments to determine if habits can spread by one individual watching another. Is the species capable of imitation? If so, this greatly strengthens the case for cultural learning in the field. Nowadays we move back and forth all the time between both sources of evidence.
But all these interesting developments happened long after my observations at Burgers’ Zoo. Following Kummer’s example, my goal at the time was to spell out what social mechanisms may underlie observed behavior. Apart from triadic awareness, I spoke of divide-and-rule strategies, policing by dominant males, reciprocal deal making, deception, reconciliation after fights, consolation of distressed parties, and so on. I developed such a long list of proposals that I devoted the rest of my career to fleshing them out, at first through detailed observations, but later also experimentally. Proposals take so much less time to make than their verification! The latter can be very instructive, though. One can set up experiments, for example, in which one individual can do another one favors, as we did with our capuchin monkeys, but then add a condition in which the partner can do favors in return. This allows favors to travel in both directions between two parties. We found that monkeys become noticeably more generous if favors can be done mutually than if only one of them has the opportunity.12 I love this kind of manipulation, since it allows far more solid conclusions about reciprocity than any observational account. Observations never quite clinch the deal the way experiments can.13
Even though Chimpanzee Politics opened a new agenda for research while introducing Machiavelli’s thinking to primatology, I was never quite happy with “Machiavellian intelligence” as a popular label for this field.14 This term implies an end-justifies-the-means manipulation of others, ignoring a vast amount of social knowledge and understanding that has nothing to do with one-upmanship. When a female chimpanzee resolves a fight between two juveniles over a leafy branch by breaking it into two and handing each youngster a piece, or when an adult male chimpanzee helps an injured, limping mother by picking up her offspring to carry it for her, we are dealing with impressive social skills that don’t fit the “Machiavellian” label. This cynical identifier made sense a few decades ago, when all animal (including human) life was customarily depicted as competitive, nasty, and selfish, but over time my own interests have drifted into the opposite direction. I have devoted most of my research to the exploration of empathy and cooperation. The exploitation of others, by using them as “social tools,” remains a great topic and is an undeniable aspect of primate sociality, but it is too narrow a focus for the field of social cognition as a whole. Caring relationships, the maintenance of bonds, and attempts to keep the peace are equally worthy of attention.
The intelligence required to effectively deal with social networks may explain why the primate order underwent its remarkable brain expansion. Primates have exceptionally large brains. Dubbed the Social Brain Hypothesis by British zoologist Robin Dunbar, the connection with sociality is supported by a relation between a primate’s brain size and its typical group size. Primates that live in larger groups generally have larger brains. I always find it hard, though, to separate social and technical intelligence, since many big-brained species are strong in both domains. Even species that hardly handle any tools in the wild, such as rooks and bonobos, may be quite good at it in captivity. It remains true, though, that social challenges have been neglected for too long in discussions of cognitive evolution, which tend to focus on interactions with the environment. Given how all-important social problem solving is in the lives of our subjects, primatologists have been right to amend this view.15
Triadic Awareness
Siamangs—large black members of the gibbon family—swing high up in the tallest trees of the Asian jungle. Every morning, the male and female burst into spectacular duets. Their song begins with a few loud whoops, which gradually build into ever louder, more elaborate sequences. Amplified by balloonlike throat sacs, the sound carries far and wide. I have heard them in Indonesia, where the whole forest echoed with their sound. The siamangs listen to one another during breaks. Whereas most territorial animals need only to know where their boundaries run and how strong and healthy their neighbors are, siamangs face the added complexity that territories are jointly defended by pairs. This means that pair-bonds matter. Troubled pairs will be weak defenders, while bonded pairs will be strong ones. Since the song of a pair reflects their marriage, the more beautiful it is, the more their neighbors realize not to mess with them. A close-harmony duet communicates not only “stay out!” but also “we’re one!” If a pair duets poorly, on the other hand, uttering discordant vocalizations that interrupt one another, neighbors hear an opportunity to move in and exploit the pair’s troubled relationship.16