Portal de Periódicos da CAPES

Getting to know the neighbours

2018; Elsevier BV; Volume: 28; Issue: 4 Linguagem: Inglês

10.1016/j.cub.2018.01.015

1879-0445

Catherine Hobaiter,

Human-Animal Interaction Studies

On a clear day from the western edge of the Budongo Forest Reserve in Uganda, where I study wild chimpanzee behaviour, I can see the Democratic Republic of the Congo. A thin horizon across the narrow Lake Albert, it would be faster as the crow flies for me to reach the vast forests of the Congo Basin — the only habitat for wild bonobos — than to reach some of the other populations of East African chimpanzees. But I, like many primate researchers, know relatively little about bonobo behaviour. A Google Scholar search for any mention of ‘bonobo’ produces a similar number of hits to searching the single (if long-studied) chimpanzee population at Gombe. Long-term field research with wild bonobos — or bilia as they are locally known — started in the 1970s with Takayoshi Kano. However, unlike the crop of long-term chimpanzee research sites taking off at the same time, repeated civil wars and limited infrastructure delayed the decades of challenging fieldwork required to study these highly social, long-lived apes. In the 1980s in the US, scientific interest was stimulated by the symbol-board prowess of Kanzi in the ‘ape language’ studies and by Frans de Waal’s pioneering comparisons of bonobo–chimpanzee behaviour. Nevertheless, today there remain relatively few places — in the wild or captivity — where it is possible to study bonobo behaviour. Besides, what’s the point? In chimpanzees, we already have a ‘closest living relative’ to compare ourselves against. Do we really need another one? Bonobos and chimpanzees diverge by less than half of one per cent in their genome. Both are forest-living apes with a fission–fusion society, they are at ease in the canopy but typically travel and rest on the ground, and are so morphologically alike that they were not recognised as distinct species until the 1920s. So far, so similar; however, other aspects of their behaviour are so different it appears astonishing that the species diverged only one to two million years ago — a heartbeat in evolutionary time. Early descriptions sought to highlight these differences, presenting the peaceful ‘make love not war’ hippy bonobo as a counterpoint to the ‘violent’ chimpanzee. But this easy distinction has been countered by a surge in recent bonobo research offering a more complete picture of their natural behaviour that includes aggressive female coalitions, hunting, and even maternal cannibalism [1Tokuyama N. Furuichi T. Do friends help each other? Patterns of female coalition formation in wild bonobos at Wamba.Anim. Behav. 2016; 119: 27-35Crossref Scopus (87) Google Scholar, 2Surbeck M. Hohmann G. Primate hunting by bonobos at LuiKotale, Salonga National Park.Curr. Biol. 2008; 18: R906-R907Abstract Full Text Full Text PDF PubMed Scopus (85) Google Scholar, 3Tokuyama N. Moore D.L. Graham K.E. Lokasola A. Furuichi T. Cases of maternal cannibalism in wild bonobos (Pan paniscus) from two different field sites, Wamba and Kokolopori, Democratic Republic of the Congo.Primates. 2017; 58: 7-12Crossref PubMed Scopus (22) Google Scholar]. We are left, appropriately, with a far more complex web of similarity and distinction between bonobo, chimpanzee, and human behaviour — one in which we are only starting to connect the dots. In Bonobos: Unique in Mind, Brain, and Behavior, Brian Hare and Shinya Yamamoto pull together the latest research investigating bonobo behaviour. Interesting in their own right, studies of bonobos also provide vital clues in teasing apart the selective forces that shaped bonobo, chimpanzee, and human behaviour. Genetically more similar to each other than they are to us, they nevertheless both exhibit some behaviour more similar to ours than to each other’s, for example, non-conceptive sex in bonobos and humans, or the use of diverse tool sets for foraging in chimpanzees and humans. This collection of work pulls together the latest perspectives from both field and captive observational and experimental research, providing an in-the-round view of our current understanding. In bonobos, we are only starting to understand fundamental aspects of social behaviour such as hierarchy, or the formation, function, and maintenance of social relationships. And the book sets the scene with work on the importance of female–female and mother–son relationships (Chapter 2) and of male–male relationships (Chapter 3), and on the role of immature individuals (Chapter 4), providing varying support for female dominance, co-dominance, or even infant ‘dominance’ (perhaps better described — as the authors discuss later on — as infant defence). Indeed, the absence of any clear age–sex class dominance seems so profound that I wonder about the appropriateness of thinking about rank in chimpanzee-like terms, or whether at times we are trying to hammer a bonobo-shaped peg into a chimpanzee-shaped hole. The comparison with chimpanzee behaviour is a central theme throughout the book. There are obvious, sound theoretical reasons why a comparison is sensible, both as a direct comparison within Pan, and as part of a broader evolutionary discussion about the cognitive capacities of common ancestor species. Nevertheless, chimpanzee researchers are only starting to come to terms with the behavioural diversity in our study species. There is no chimpanzee species-strategy for male hierarchy, sexual behaviour, hunting, female–female relationships, even tool-use, and so on. These can vary dramatically from group to group and within groups over time. It is risky then, as happens here at times, to compare single communities within both species to highlight differences between ‘bonobo’ and ‘chimpanzee’ behaviour. Different communities might present more or fewer dramatic contrasts. But it would be unfair to suggest that there are not clear species differences. It only takes a cursory first read to recognise that even an understanding of chimpanzee behaviour across populations leaves you unprepared for the findings on bonobos; descriptions such as peaceful, female-led intergroup encounters (p. 29) are both unthinkable and captivating from the perspective of a chimpanzee researcher. The general focus on social cognition is evident from the book’s contents list; 12 of the 17 chapters are dedicated to the topic. As a researcher who believes that an understanding of species-specific cognition is best rooted in an understanding of the ecological niche to which the species is adapted, it was initially disconcerting to dive headfirst into a discussion of social relationships and cognition. The importance of ecology is not overlooked; indeed, several authors highlight that the increased density and reliability of available food in bonobo habitats, and the associated reduction in foraging and travel costs, may underpin such fundamental Pan species differences as social tolerance, or female gregariousness and dominance. So, while there is a useful discussion of large-scale habitat and speciation at the end (Chapter 16), a short introduction on bonobo habitat may still have been useful. Nevertheless, individual chapters do a solid job of presenting the aspects relevant to their particular focus. A particular challenge in studies of comparative social cognition is that we are typically reliant on external behaviour as an imperfect, but visible, clue for determining internal states of mind. Central chapters focus on what bonobos can contribute to our understanding of features such as theory of mind (our ability to see others as distinct individuals whose knowledge may differ from our own, described in Chapter 6), or language (whether in their acquisition of human-like languages — Chapter 7 — or the capacity for language-like features in their natural communication, described in Chapter 8). There is no panacea, but the valuable lessons learned in the decades of comparative research with chimpanzees are reflected in the work being done on bonobos. Early tests of chimpanzee social cognition often required two individuals to work cooperatively to obtain a food reward, and resulted in the repeated failure to show even relatively simple perceptual abilities, such as perspective taking. I have seen active sharing of food and remarkable tolerance in wild chimpanzees. However, typical chimpanzee foraging is better described by the frequent image of an individual screaming the tree down because, despite being surrounded by hundreds of apparently similar figs, someone else got the one fig it really wanted. Chimpanzee foraging is, by and large, competitive. Brian Hare and colleagues pioneered the shift to a competitive paradigm for testing the expression of chimpanzees’ cognitive skills [4Hare B. Call J. Agnetta B. Tomasello M. Chimpanzees know what conspecifics do and do not see.Anim. Behav. 2000; 59: 771-785Crossref PubMed Scopus (621) Google Scholar] and, as a result, a suit of new findings emerged describing apes’ previously unrecognised social abilities, culminating in the recent work demonstrating recognition of false beliefs [5Krupenye C. Kano F. Hirata S. Call J. Tomasello M. Great apes anticipate that other individuals will act according to false beliefs.Science. 2016; 354: 110-114Crossref PubMed Scopus (339) Google Scholar]. So it is particularly welcome here to see the pairing of chapters from field observation and captive experiments in Sections 4 and 5. The reports of food sharing in wild bonobos (Chapter 9) highlight the lack of obvious reciprocity or nutritional need (the fruits shared are abundant and could be easily foraged individually). Nevertheless, food sharing is common, suggesting that it may be the social act of sharing that is important. These observations offer context to findings from captivity (Chapters 10–12) showing that sharing decreases between bonobos when there is no option to physically interact, and that they tend towards social versus technological solutions to problem solving. Similarly, the finding that dominant individuals share food in the wild, apparently without any reciprocal benefit in terms of reproduction, social support, or grooming, strengthens the view that bonobos are proactive in their prosocial behaviour, and contrasts nicely with the findings in chimpanzees in which reciprocal benefits are more material (e.g. ‘food for sex’) and sharing typically follows persistent begging or harassment.Behavioural comparisons. Chimpanzees in the Budongo Forest Reserve, Uganda. Decades of comparative research have used chimpanzee behaviour and cognition as a point of comparison for human behaviour, with differences between them used to suggest human-specific characteristics. However, the last common ancestor of chimpanzees and humans was also shared with bonobos, whose behaviour and cognition show a novel pattern of similarities and distinctions.View Large Image Figure ViewerDownload Hi-res image Download (PPT) Given the striking differences in the species’ social tolerance and the behavioural plasticity demonstrated across chimpanzee populations, one challenge in comparing chimpanzee and bonobo cognition is determining whether differences in behaviour reflect differences in cognitive abilities, or differences in the expression of the same basic ability within very different environments. Post-mortem analyses appear to show species differences in brain structure, such as grey matter variation around the hippocampus, and are discussed in relation to species differences in behaviour, for example, spatial problem solving (Chapter 14). However, sample sizes remain too small to draw strong conclusions at present, particularly given the potential impact of variation in life history. Over the chapters, the picture that builds up defies easy pigeonholing. Bonobos are xenophylic, responding positively to social strangers, but they are also less bold than chimpanzees, being less likely to explore and exploit novel physical environments. Capable and spontaneous tool users in captivity, they rarely employ these skills in the wild. The highest ranking individual in a community will be female, but, after that, there is no clear age–class ordering of rank, and what does rank mean in a species with limited reproductive skew, high social tolerance, and regular and proactive prosocial sharing of resources? The apparent selection for prosociality and cooperation and against aggression is argued (Chapter 14) to be evidence for ‘self-domestication’ within natural selection (in contrast to similar effects on domesticated species, such as dogs or cattle, as a product of human-driven artificial selection). Substantial further research is needed to complete the picture, but it is clear that an understanding of both bonobo and chimpanzee behaviour is necessary to provide a viewpoint from which to investigate the evolution of human social cognition. However, there are urgent challenges to doing so (Chapters 17 and 18). The rapid expansion of infrastructure throughout the DRC provides development opportunities for local communities, but for the already endangered bonobo it brings habitat destruction and degradation, exposure to disease, and increased hunting. Given limited resources, it becomes vital to accurately describe local conservation environments and to target action to both the places of most need and the areas in which success is most likely (see, for example, work in Chapter 18 modelling future sanctuary population density). As Hare and Yamamoto highlight (p. 7), long-term success will require a significant part of this challenge to be met from within the DRC, by Congolese-led research. The founding in 2017 of the African Primatological Society represents a significant stride towards providing the infrastructure for African-led primate research and conservation. It will take continued international drive to support the emergent research culture and see our understanding of bonobo mind and behaviour grow beyond its promising infancy.