Thursday, 23 June 2022

Evolution News - How Humans Evolved to Get Along With Neighbours

Shared grooming among bonobos is indicative of their group dynamics, which includes tolerance and cooperation.

Photo: Martin Surbeck
Bonobos’ tolerant, peaceful group relationships paved way for human peacemaking – Harvard Gazette

Despite our long history of often religiously-inspired wars, and divisions into mutually-hostile camps, humans are actually quite good at getting along with neighbouring social groups, and peace-making is generally considered a noble activity, while war-mongering is generally despised.

In this respect we much more closely resemble the peaceable bonobos with whom we share 99% of our genes, than the equally closely related chimpanzees.

Not surprisingly, because it is an innate human trait, early Christians tried to claim credit for the idea that peace-making is a skill to be admired, with "Blessed are the peace-makers". The pity is, because they only saw things in selfish terms, they made it look like something only worth doing for a personal reward and not for the greater social good, because it leads to greater human happiness. Ironically, with peace-making featuring in their Beatitudes (Matthew 5:9), it may well be the result of evolution and an indication of our common ancestry with the bonobo.

But how did we get this way?

Attempting to answer this, a group of three scientists led by Liran Samuni of Harvard University Department of Human Evolutionary Biology, and the Department of Human Behaviour, Ecology and Culture, Max Planck Institute of Evolutionary Anthropology, Leipzig, Germany and Martin Surbeck, also of Harvard and the Max Planck Institute, and including Kevin Langergraber of the School of Human Evolution and Social Change, and the Institute of Human Origins, Arizona State University, Tempe, Arizona, USA, spent three years studying four groups of bonobos who peacefully co-exist in the Kokolopori Bonobo Reserve in the Democratic Republic of Congo.

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Grooming interaction
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Their findings were published open access a couple of days ago in the journal, Proceeding of the National Academy of Science (PNAS), although, sadly, only the abstract is freely available.

Juan Siliezar, writing in the Harvard Gazette, explains:
Humans display a capacity for tolerance and cooperation among social groups that is rare in the animal kingdom, our long history of war and political strife notwithstanding. But how did we get that way?

Scientists believe bonobos might serve as an evolutionary model. The endangered primates share 99 percent of their DNA with humans and have a reputation for generally being peace-loving and sexually active — researchers jokingly refer to them “hippie apes.” And interactions between their social groups are thought to be much less hostile than among their more violent cousins, the chimpanzees.

Some, however, have challenged this because of a lack of detailed data on how these groups work and how they separate themselves.

It was a very necessary first step. Now that we know that despite the fact that they spend so much time together, [neighboring] bonobo populations still have these distinct groups, we can really examine the bonobo model as something that is potentially the building block or the state upon which us humans evolved our way of more complex, multilevel societies and cooperation that extends beyond borders.

There aren’t really behavioral indications that allow us to distinguish this is group A, this is group B when they meet. They behave the same way they behave with their own group members. People are basically asking us, how do we know these are two different groups? Maybe instead of those being two different groups, these groups are just one very large group made up of individuals that just don’t spend all their time together [as we see with chimpanzee neighborhoods].

Dr Liran Samuni, lead author
A postdoctoral fellow
Harvard’s Pan Lab
Department of Human Evolutionary Biology,
Harvard University, Cambridge, MA, USA
And the Department of Human Behaviour, Ecology and Culture
Max Planck Institute of Evolutionary Anthropology, Leipzig, Germany

The research, published in PNAS, shows that the four neighboring groups of bonobos they studied at the Kokolopori Bonobo Reserve in the Democratic Republic of Congo maintained exclusive and stable social and spatial borders between them, showing they are indeed part of distinct social groups that interact regularly and peacefully with each other.


The study is a result of three consecutive years of observing the bonobo community in the Kokolopori reserve from 2017 to 2019. Previous research showed evidence of the 59 bonobos forming four separate groups that routinely crossed paths to interact, groom each other, and share meals. What hasn’t been clear is the extent to which the behavior of these bonobo groups resembles that of chimpanzee subgroups that form within one larger community.

Primatologists refer to chimp subgroups, which are highly territorial and hostile to those in different communities, as neighborhoods. Essentially, members of these subgroups don’t spend all their time together as part of one large group but are all still part of it, maintaining relationships with each other and (most importantly) not battling each other when they meet.

Bonobos have been far less studied than chimps due to political instability and logistical challenges to setting up research sites in the forests of the Democratic Republic of Congo, the only place where the primates are found. In addition, studying relationships among and between Bonobo groups has been further complicated by the fact that subgroups appear to intermingle with some frequency.


To get at the answer, at least two observers from the reserve followed each bonobo group daily from dawn to dusk, recording behavioral and location data that was then analyzed.

The researchers primarily tracked how much time individual bonobos spent together, with whom, and what activities they engaged in. This helped the researchers perform a statistical method called a cluster analysis. This method groups data points in a cluster so that points from the same group are clustered closely on a plot, while data points not in the same group are clustered in another space.

Essentially, they tracked which bonobos shared significant associations with one another, which ones tended to come together for meals more often, which ones tended to stick together when faced with a choice of whom to go with, and which ones interacted more in the same home range. This helped them draw clear distinctions between what bonobos were part of the same group and when members of one group were peacefully interacting with neighboring groups across each other’s borders.

They compared this to data collected on 104 chimpanzees that lived in the Ngogo community in Uganda’s Kibale National Park between 2011 and 2013.

The researchers found the bonobo clusters were overall more consistent and stable than the subgroups of chimps. This suggests that the bonobos within each cluster had a stronger social preference for one another than was seen within chimpanzee subgroups.

There are very few [bonobos] left. We gather here information that potentially will not be available anymore in 50 years if things continue the way they do.

Martin Surbeck, Senior author
Principle investigator, Harvard’s Pan Lab
Department of Human Evolutionary Biology,
Harvard University, Cambridge, MA, USA
And the Department of Human Behaviour, Ecology and Culture
Max Planck Institute of Evolutionary Anthropology, Leipzig, Germany
When it comes to the Kokolopori bonobos, this helped the researchers not only confirm the four groups — which they named the Ekalakala, the Kokoalongo, the Fekako, and the Bekako — but also come up with a reliable way to predict which bonobos were most likely to stick together when the different groups of bonobos met and separated.

Samuni and Surbeck, an assistant professor in the Department of Human Evolutionary Biology and the paper’s senior author, say the results show that bonobos, like humans, are capable of complicated relationships outside their immediate core network.

Now that the researchers have firmly established that these bonobos have distinct groups, they want to dig further into what cooperation and trade look between these groups and whether it can potentially represent what it looked like in our common ancestor. This would help explain how humans, to an extent, overcame antagonism between different groups and developed peaceful cooperation.
The authors give more detail in the abstract to their paper in PNAS:

In striking contrast to chimpanzees, tolerant between-group interactions in bonobos, our other closest living relative, have been suggested as a pathway to understanding the evolution of human between-group peacemaking and cooperation. However, due to the lack of data on bonobo group dynamics and partitioning, bonobo between-group tolerance has been routinely challenged. Here, we compared the social systems of bonobos and chimpanzees to find distinct and stable social groups in bonobos that interact regularly and peacefully. Despite their tolerant meetings that exceed the rates previously described between human groups, bonobo groups maintained exclusive social and spatial borders. Tolerance occurring between socially distinct groups highlights the potential of bonobos as a referential model for the evolution of between-group cooperation in humans.


Human between-group interactions are highly variable, ranging from violent to tolerant and affiliative. Tolerance between groups is linked to our unique capacity for large-scale cooperation and cumulative culture, but its evolutionary origins are understudied. In chimpanzees, one of our closest living relatives, predominantly hostile between-group interactions impede cooperation and information flow across groups. In contrast, in our other closest living relative, the bonobo, tolerant between-group associations are observed. However, as these associations can be frequent and prolonged and involve social interactions that mirror those within groups, it is unclear whether these bonobos really do belong to separate groups. Alternatively, the bonobo grouping patterns may be homologous to observations from the large Ngogo chimpanzee community, where individuals form within-group neighborhoods despite sharing the same membership in the larger group. To characterize bonobo grouping patterns, we compare the social structure of the Kokolopori bonobos with the chimpanzee group of Ngogo. Using cluster analysis, we find temporally stable clusters only in bonobos. Despite the large spatial overlap and frequent interactions between the bonobo clusters, we identified significant association preference within but not between clusters and a unique space use of each cluster. Although bonobo associations are flexible (i.e., fission–fusion dynamics), cluster membership predicted the bonobo fission compositions and the spatial cohesion of individuals during encounters. These findings suggest the presence of a social system that combines clear in-group/out-group distinction and out-group tolerance in bonobos, offering a unique referential model for the evolution of tolerant between-group interactions in humans.

Samuni, Liran; Langergraber, Kevin E.; Surbeck, Martin H. (2022) Characterization of Pan social systems reveals in-group/out-group distinction and out-group tolerance in bonobos
Proceedings of the National Academy of Sciences (PNAS)
; 119 (26) e2201122119; DOI: 10.1073/pnas.2201122119

Copyright: © 2022 The authors.
Published by National Academy of Science of the United States of America (PNAS). Open access
Reprinted under a Creative Commons Attribution-NonCommercial-NoDerivatives License 4.0 (CC BY-NC-ND).
It seems then that our ability to make peace and generally get along, despite any tendency to territorial competition and hostility to out-group members as manifested in xenophobia, for example, and notwithstanding the frequent violent classes between members of different religious groups in human society and intolerance for different cultured, is closer to that of the bonobo than our more violent, intolerant cousins, the chimpanzees. The advantage this gives us, as with bonobos, is greater exchange of information as shown by the spread of technologies and customs between human groups, whereas chimpanzees rarely acquire new information from other chimpanzee groups.
This could itself be a key to our cultural success as a species.

It could also be why countries which tend to be isolationist and xenophobic tend in the long run to stagnate.

Thank you for sharing!

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