by Ingrid Fadelli, Phys.org
edited by Sadie Harley, reviewed by Robert Egan
Both bonobos and dolphins form unexpected alliances with ‘outsiders’
Dodger with calf and Alley Cats landscape. Credit: Stephanie King.
Cooperation is a pillar of human society, promoting an exchange of skills and knowledge between different individuals and social groups. Humans typically do not only cooperate with their own family, friends and members of their community, but also with others who are unrelated to them and are outside of their social circle.
This ability to cooperate with “outsiders” has long been considered rare in non-human primates and other animal species. Over the past few decades, however, out-group cooperative behaviors were observed in various other species, including bonobos and bottlenose dolphins.
Researchers at the Leibniz Institute for Primate Research, Harvard University, Florida International University and University of Bristol recently summarized their respective observations of between-group cooperation in bonobos and bottlenose dolphins.
Their review paper, published in the journal Proceedings of the Royal Society B: Biological Sciences, pinpoints social and ecological conditions that support cooperation with other social groups in both species, offering insight into how this ability might have evolved in humans.
“Our paper grew directly out of independent fieldwork on bonobos and bottlenose dolphins,” Liran Samuni, first author of the paper, told Phys.org.
“For decades, members of our teams have studied these species at long-term field sites, and in both systems, we documented repeated, peaceful interactions between individuals from different social groups. These tolerant, and in some cases cooperative, relationships with outgroup members stood out because they are so rare in most animals.
“The immediate reason our teams came together was a public e-letter from the dolphin group critiquing the one-sided depiction of between-group cooperation in a bonobo paper. Instead of leading to a dispute, this exchange prompted us to meet and discuss the phenomena in both systems.”Flute and Monkey Mia. Credit: Stephanie King.
Combining bonobo and dolphin observations
When they started communicating, the two research teams studying bonobos and bottlenose dolphins realized that they were observing strikingly similar patterns in the two very different species. This inspired them to write a collective paper that synthesized their respective observations.
“Our collaboration builds on three main strands,” said King, a co-author of the study. “First, the depth of long-term behavioral data in both bonobos and dolphins allows us to move beyond isolated anecdotes and examine intergroup relationships systematically.
“Second, bonobos and dolphins differ markedly in their ecology, evolutionary history, and sociality, yet both show stable, cooperative ties between groups—a convergence that demands explanation. Third, there is an active debate in human evolution about when and why friendly, cooperative relations between communities emerged.”
As part of their study, Samuni and her colleagues looked at bonobo and bottlenose dolphin observations side by side. Their paper summarizes findings about cooperation with outsiders in the two species, while also pinpointing the ecological, social and cognitive conditions that appear to support these inter-group relationships.
“We also considered what these cases tell us about the evolution of intergroup cooperation more generally, including in humans,” said Samuni. “We use the behavior of bonobos and dolphins as comparative case studies to clarify when and how cooperative relationships can extend beyond the boundaries of one’s own group.”Bonobo grooming. Credit: Martin Surbeck, Kokolopori Bonobo Project.
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Reviewing years of fieldwork at different sites
The team’s review paper draws on years of detailed observations collected at various sites where the two species live. Dolphins were observed by the Shark Bay Dolphin Research team in Shark Bay, in Australia. Bonobos, on the other hand, were observed as part of the Kokolopori Bonobo Research project, which followed habituated animals daily in the Democratic Republic of the Congo.
“We track bonobos from the moment they wake up until they build their night nests, and because every individual is recognized, we can record both their activities and their relationships in detail,” explained Martin Surbeck, director of the Kokolopori field site and a co-author of this study.
“This includes what they eat, where they travel, and all their social interactions—who spends time together, who grooms whom, who fights, and who offers support or shares food.”
The dolphin findings summarized in the team’s paper were collected both by observing the animals living in Shark Bay and during field experiments. Individual dolphins who were habituated to the presence of humans were followed over the course of several years and their social behaviors were recorded.Bonobo mother and offspring. Credit: Liran Samuni, Kokolopori Bonobo Project.
“Using drones, we can track the dolphins when they are underwater and record fine-scale information on behavioral interactions between individuals,” said Stephanie King, co-author of the paper. “We can also conduct sound playback experiments to investigate communication functions and questions centered around social cognition.”
The exceptionally rich set of observations collected by the researchers allowed them to map both bonobo and dolphin social networks in detail. In addition, the team tried to identify the mechanisms underpinning specific cooperation patterns, such as the role of kinship, long-term friendships and the prosocial tendencies of specific animals.
“We also frequently observed and recorded what happened when different groups meet in both species,” explained Surbeck. “During these encounters, we monitored who interacted with whom, how long relationships last, and how social benefits (such as alliance support or access to mating and food) are distributed.”
New insight into animal cooperation
The observations gathered by Samuni and her collaborators show that both bonobos and dolphins can form strong and long-lasting ties with other individuals from a different social group. Notably, the inter-group relationships they establish appear to be at least partly strategic, as they can benefit their lives and those of their communities.
“We hope that our paper will shape how researchers think about intergroup relationships going forward,” said Richard Connor, co-author of the paper.
“Our synthesis brings together long-term evidence from bonobos and bottlenose dolphins, two very different species that nonetheless show repeated, peaceful, and cooperative interactions between social groups. These systems are usually discussed in isolation; by placing them side by side, we highlight parallels in the conditions promoting tolerance and cooperation with outgroup members.”
The researchers’ review paper shows that inter-group cooperative behaviors are not rare anomalies and might be more common than anticipated. In fact, both bonobos and bottlenose dolphins can establish strong, durable ties with members of other groups, which offer access to ongoing support, information, resources and new mating opportunities.
“From this comparative perspective, we identify a set of ecological and social conditions that may enable intergroup cooperation—for example, protracted development and advanced socio-cognitive abilities that support learning about the social world, and a reduction in the payoff of competitive strategies for securing food (in bonobos) or mates (in dolphins),” said Surbeck.
In their paper, the team argue that intergroup relationships are better understood as a continuum, as opposed to a dichotomy between conflict and tolerance. In other words, there might not be such a black and white distinction between conflict and tolerance, as both bonobos and monkeys can cooperate with members of other groups to highly varying degrees.
“A common view has been that humans are unique in forming costly, cooperative relationships with non-kin across group boundaries, a pattern often attributed to cultural institutions, shared norms, and sophisticated kin-recognition and tracking systems,” said Connor.
“Our joint work challenges this assumption by showing that bonobos and dolphins also engage in forms of cooperation with outgroup members that can be individually costly in the short term—for example, by investing time and energy in affiliative bonds, sharing resources, or offering coalitionary support without immediate repayment.”
Directions for future research
The synthesis of bonobo and bottlenose dolphin intergroup relations suggests that under specific ecological and social conditions, stable cooperative ties can emerge across groups, even in species without the refined cultural nuances observed in humans.
In the future, the team’s findings could inspire other biologists to further investigate intergroup cooperation, to uncover features that are truly unique to humans and others that are shared with other species.
“Our work could lay a foundation for future comparative research,” said Samuni. “An important next step will be to broaden the phylogenetic scope, particularly by including additional species that, like bonobos and dolphins, show both cooperative and hostile relationships between groups rather than being obligatorily tolerant or uniformly hostile.
“Studying such systems would allow us to ask which ecological conditions, demographic changes, or social dynamics drive shifts along the spectrum from tolerance to overt conflict, and to evaluate whether the patterns we identify in bonobos and dolphins generalize more broadly.”
In their review paper, the researchers identified a few questions and themes that could be addressed in future research. Firstly, new studies could try to shed more light on how cross-group relationships are maintained over time.
“How do cooperative relationships between groups actually emerge and persist?” said King. “In both bonobos and dolphins, we now know that individuals can form stable, sometimes costly ties with outgroup partners, but we still do not know how these relationships get started, what developmental experiences or individual traits make them more likely, or whether there are mechanisms in place to sustain such exchange.”
The team would eventually like to better understand the mechanisms that underpin the cooperative interactions they observed in bonobos and dolphins. For instance, they would like to identify behaviors that animals use to initiate or reinforce ties with members of other groups. These could include things like grooming, socio-sexual contact, vocal exchanges or synchronous movement.
“We are also curious to find out whether certain ‘broker’ individuals are especially important in forging or maintaining cross-group links,” explained Surbeck.
“At the same time, we are interested in the socio-cognitive side, or in other words, how much individuals know about others’ relationships, whether they track third-party alliances across groups, and how they use that information when choosing cooperative partners.”
Finally, the researchers have not yet determined the extent to which inter-group relationships remain stable over time. In nature, circumstances can change, whether due to gradual ecological shifts or sudden events. These changes might also influence the relationships between different groups.
“Comparative work across sites and, ultimately, additional species will be essential for testing whether the patterns we see in bonobos and dolphins generalize more widely, and for understanding the benefits but also the potential risks (for example, disease transmission) that come with maintaining cooperative ties across group boundaries,” added Samuni.
Exposing the Big Game 