Bonobo and Chimpanzee: The Lessons of Social Coexistence

By Takeshi Furuichi

This book describes the similarities and differences between two species, bonobos and chimpanzees, based on the three decades the author has spent studying them in the wild, and shows how the contrasting nature of these two species is also reflected in human nature. 

The most important differences between bonobos and chimpanzees, our closest relatives, are the social mechanisms of coexistence in group life. Chimpanzees are known as a fairly despotic species in which the males exclusively dominate over the females, and maintain a rigid hierarchy. Chimpanzees have developed social intelligence to survive severe competition among males: by upholding the hierarchy of dominance, they can usually preserve peaceful relations among group members. In contrast, female bonobos have the same or even a higher social status than males. By evolving pseudo-estrus during their non-reproductive period, females have succeeded in moderating inter-male sexual competition, and in initiating mateselection.  Although they are non-related in male-philopatric society, they usually aggregate in a group, enjoy priority access to food, determine which male is the alpha male, and generally maintain much more peaceful social relations compared to chimpanzees.   

Lastly, by identifying key mechanisms of social coexistence in these two species, the author also seeks to find solutions or “hope” for the peaceful coexistence of human beings.

"Takeshi Furuichi is one of very few scientists in the world familiar with both chimpanzees and bonobos. In lively prose, reflecting personal experience with apes in the rain forest, he compares our two closest relatives and explains the striking differences between the male- dominated and territorial chimpanzees and the female-centered gentle bonobos."

Frans de Waal, author of Mama’s Last Hug - Animal Emotions and What They Tell Us about Ourselves (Norton, 2019)

   

• Language: English
• Publisher: Springer
• Release date: Nov 22, 2019
• ISBN: 9789811380594

Book preview

© Springer Nature Singapore Pte Ltd. 2019

T. FuruichiBonobo and ChimpanzeePrimatology Monographshttps://doi.org/10.1007/978-981-13-8059-4_1

1. The Life of Bonobos in a Tropical Rainforest

Takeshi Furuichi¹ 

(1)

Primate Research Institute, Kyoto University, Inuyama, Aichi, Japan

The original version of this chapter was revised. A correction to this chapter can be found at https://​doi.​org/​10.​1007/​978-981-13-8059-4_​6.

1.1 I Would Really Rather Be Like a Bonobo

1.1.1 Which One?

Which one do you think you would prefer to be, a bonobo or a chimp? I inadvertently took a deep breath and looked around. It was summer 2005 and I was just finishing an interview with a BBC reporter at the British Embassy in Kinshasa, the capital of the Democratic Republic of the Congo (DR Congo). A variety of trees and ornamental flowers were planted in a large and carefully tended garden. The red flowers of African ginger added a vibrant color. It was as if I was at a corner of a lush botanical garden exhibiting tropical vegetation.

Sitting in a chair in the center of this garden, the TV camera and microphone were pointed at me. After attending an international conference on bonobo conservation held in Kinshasa, I was being interviewed for a documentary about the research and conservation activities on wild bonobos that the Japanese colleagues and I have been engaging in.

I am, to some extent, used to answering questions related to things like the history of our research, since my mentor, Takayoshi Kano, launched in 1973, the behavioral ecology and social structure of bonobos we have discovered, and similarities and differences in behavioral ecology between the bonobo and the chimpanzee, both of which are the most closely related species to humans. But to answer this last question, I had to look deep inside myself. I answered unusually deliberately so as to carefully choose the following words: Perhaps, if I must choose, I think I would rather be like a bonobo, but when I consider my inner self, I think that I am actually a chimpanzee.

1.1.2 What Is a Bonobo?

What kind of animal is the chimpanzee? Without getting into scientific details, I think most people know something about this species. The chimpanzee, which lives mainly in the tropical forest zone across equatorial African continent is known as the closest living relative to humans and the smartest of all animals. Chimpanzees have appeared in pop-culture around the world, made popular because of their high intelligence and human-like qualities.

In comparison, the public knowledge about the bonobo is remarkably low. Until about 10 years ago, when I asked, Who knows about the bonobo? to about 300 undergraduate students in one of my lectures, I was pleased if a few students raised their hands. Recently, this number has increased, but there are still probably no more than ten students who can immediately say off the top of their heads, Oh, yes, the bonobo, that animal.

Like the chimpanzee (Pan troglodytes spp.), the bonobo (Pan paniscus) is also an African great ape species that lives in the Congo Basin near the equator in Central Africa. Its habitat area is separated from that of the chimpanzee by the large river that flows around the Congo Basin in an arc (Fig. 1.1). The chimpanzee and the two gorilla species that inhabit the in the northern side (right bank) of the Congo River have been discovered more than 300 years ago by explorers during colonization of Africa by a number of European countries. It was not until about 90 years ago that people realized that the bonobo was a new, separate great ape species that had previously not been discovered. There are two main reasons why the discovery of the bonobo was delayed. One reason was that the bonobo inhabits a remote and isolated area that was largely inaccessible to early explorers and European colonists. I suspect that although a number of explorers traveled up the Congo River, such as Henry Morton Stanley and Andre Jeyd, who was also known as a novelist, they did not dare to venture into the dark tropical rainforest that spreads in this area.

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Fig. 1.1

Distribution ranges of the bonobo and three subspecies of the chimpanzee. (Modified from Figure 1 in Ahuka-Mundeke et al. 2016)

Another reason why early explorers and European colonists did not encounter the bonobo is that the physical appearance of the bonobo is very similar to the chimpanzee (Fig. 1.2). When one looks at their photographs, it is hard to tell which is which, unless you are an enthusiast.

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Fig. 1.2

Chimpanzee (left) and bonobo (right)

There is only one easy way to distinguish between chimpanzees and bonobos. A juvenile chimpanzee has a whitish face (all chimpanzees that appear on the TV have a whitish-pinkish face because all of them are juvenile). A juvenile bonobo, the face is black from infancy. However, adults of both species have a black face. So, adults can be very difficult to distinguish by non-experts. There are also various diagnosable characteristics in adults; for example, while the chimpanzee has a solid physique, the bonobo is somewhat skinnier with longer limbs. It is slightly smaller in body size and in stature. The frontal hair in adult chimpanzees is more prone to baldness, while the frontal hair in adult bonobos is parted in the middle.

1.1.3 History of the Bonobo Discovery

Before being confirmed as a new species, bonobos must have been captured again and again and taken to European zoos, exhibited as museum specimens, and sold as pets; however, due to its close resemblance to the chimpanzee, no one would have thought the bonobo was a different species. There is a lot of evidence that bonobos were exported abroad before the scientifically significant discovery of the bonobo. For example, Robert Yerkes, the founder of primatology, raised some chimpanzees for behavioral observation at an American research laboratory. We now believe that one of Yerkes’ chimpanzees, named Prince Tim, was actually a bonobo. Yerkes was surprised by the fact that Tim was extraordinarily intelligent and extroverted. Yet, he had a more agreeable personality than other chimpanzees. He reported the details of Tim’s behavior in his 1924 book, Almost Human. Although Yerkes, with scholarly prowess, thought that Tim was a different species from the chimpanzee or a peculiar species, even he, with expertise in primatology, could not confirm his idea.

Four years later in 1928, the discovery of the bonobo as a new species happened in a museum in Europe. Ernst Schwarz, a German morphologist, was examining chimpanzee skull samples that had arrived at a museum in Belgium. Belgium was the colonizer of the Colonial Empire of the Belgian Congo (now the DR Congo) where bonobos live. Schwarz found that among the samples, some skulls were smaller than others despite the fact that they were all clearly adults. Based on his research, Schwarz reported that he had discovered a new species of chimpanzee (P. paniscus) – and gave it the common name pygmy chimpanzee – in a conference [1]. In response to this report, several bonobos were shipped out from the Congo Basin to the United States. After further investigation, the bonobo was officially recognized as a new species in 1929.

Let me also touch on the discovery of the bonobo in Japan. In 1980, when Japan had not yet ratified the Washington Convention, an animal dealer in Tokyo imported a male-female bonobo pair from Belgium. In postwar Japan, when entertainment was scarce, mobile zoos played an active role in many local areas. They moved from town to town in a vehicle, exhibiting animals that children normally did not get to see, and took admission fees. The female bonobo died shortly after landing in Japan, but the surviving male was likely used in one of these mobile zoos. As Japan entered an economic growth period, mobile zoos declined in popularity. The male bonobo was moved around and finally taken to a small amusement park called Beppu Rakutenchi in the middle of the mountains in Ōita Prefecture in Kyushu, but keeping him in captivity became difficult. Then, in 1998, the Japan Monkey Center in Inuyama City, Aichi Prefecture, decided to adopt him. It was there that I saw this bonobo named Peasuke, a young bonobo of about 10+ years of age with a gentle face. He moved his body following the movement of visiting children outside his enclosure. Peasuke loved children very much.

He eventually crossed the ocean to go to the United States for breeding purposes. In those days, there were only about 80 bonobos in captivity in the world, and most of them were the descendants of that first male brought to the United States from the Congo Basin. Therefore, most of them were relatives that were too close for breeding purposes. Suddenly came this discovery of the Japanese bonobo, Peasuke, whose place of origin was completely unknown. He became the ideal star in a bonobo breeding program that needed to avoid inbreeding.

Peasuke was on loan to the United States, was given a spacious living space, and had four offspring with two females. Sadly, he was unable to come back to Japan when his life ended due to an illness in 2006, but at least he must have led a happier life compared to when he was in the mobile zoo.

With the discovery of the bonobo, the world of anthropology slipped into turmoil, which is understandable. It is estimated that there are 8 million living species of eukaryotes in the world, and yet only about one-seventh of them have been discovered. The majority of undiscovered species are insects, plants, fungi, and other organisms that live in dense tropical rainforests where tree crowns overlap as the canopy, or in the mud at the bottom of the deep ocean, or in other places where biologists have not yet investigated. Most large mammals have already been discovered. And yet, a new great ape species was discovered at the beginning of the twentieth century. Moreover, it is as closely related to humans as is the chimpanzee.

The evolutionary relationships of the great apes have now been determined via morphological and genetic analyses (Fig. 1.3). The great apes include three orangutan species that inhabit tropical rainforests in Asia, and two gorilla species, the chimpanzee, and the bonobo that all live in Africa. Until recently, humans were not included in the group of apes, because it was thought that humans had separated from the apes more than 20 million years ago, but now our species is included in this group called the family Hominidae.

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Fig. 1.3

Phylogeny of the Hominidae

From this group of apes, the orangutans was the first to diverge. After the orangutan, the gorilla branched out from the ancestral species of all the African great apes. The next was the human. Finally, the last great apes that branched out at about 1 million years ago were the chimpanzee and the bonobo. Therefore, the bonobo and the chimpanzee are both equally the closest living relatives to humans, followed next by the two gorilla species. Based on this phylogenetic tree, although the chimpanzee and bonobo resemble gorillas in external appearance, they have closer affinities to Homo sapiens than they do to the gorillas.

The bonobo, or the last great ape to be discovered, has many similarities with the human besides evolutionary relationships. First of all, morphologists were surprised that the genus Australopithecus, one of the human ancestral genera dated 2–4.5 million years ago, is morphologically quite similar to the bonobo. Like Australopithecus, the bonobo had a rounded head, similar limb length and proportions, and even a linearly stretched backbones near the pelvis when standing up. Because of this last shared trait, the bonobo is good at upright bipedal locomotion. Bonobos usually knuckle-walk quadrupedally, but when they walk while carrying food in their hands, they can walk a long distance bipedally far better than chimpanzees (Fig. 1.4). Perhaps because of this posture, they sometimes engage in sexual intercourse in a face-to-face, ventral-ventral position or the so-called missionary position in humans (Fig. 1.5). It should be noted here that they also use sexual intercourse for purposes other than reproduction.

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Fig. 1.4

A female, carrying two offspring, walks with sugarcane in her hands

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Fig. 1.5

Ventral-ventral copulation in the bonobo

It is no wonder that anthropologists became excited about the idea that they had found a living ancestral human species. Among them was the morphologist, Adrienne L. Zihlman, who wrote an article stating that the bonobo is the best representation of the common ancestor of humans, chimpanzees, and bonobos [2]. That is to say, it is like a living fossil of our common ancestor. This generated heated discussions.

1.1.4 What Do Bonobos Teach Us?

The living fossil is a term that we hear often, but it is actually hard to understand.

Since life began on Earth, organisms have changed their shapes in multitudes of ways, branching out to evolve into new species and some eventually have gone extinct, providing space for other organisms. Most organisms that have ever existed on the Earth have already gone extinct, which means that organisms that are alive today are the species that happen to exist at the cutting edge of the present time. In the geological strata, we can find fossils of extinct species, if conditions such as climate and geographical features are favorable and the organisms that lived in the past have escaped the decaying process. If some organisms from the past continue to live to the present without changing much of their physical appearance and behavior, they are called living fossils.

For example, the coelacanth, which is a prime example of living fossils, lived in freshwater zones and shallow water during the Devonian period in the Paleozoic era about 400 million years ago when amphibians arose from fish. One species still lives in the deep sea of the Comoro Islands off the coast of Africa, and another species lives in the Celebes Sea, north of Sulawesi in Indonesia, and because they have retained various primitive features, they are called living fossils. When we look at a living fossil, we are captivated by the illusion that we are witnessing the ancient world as if we were on a time machine, and our heart is captivated by the romance from a tremendously long time ago. Furthermore, because shown in front of us is not the living fossil of the amphibian ancestor, rather a living fossil of the last common ancestor of humans and the African great apes, our hearts feel even more enchanted.

However, those organisms we call living fossils are not frozen in time, but they have evolved as they have undergone repeated struggles for existence and now existing as contemporary species that are adapted to the current environment. Just look at the coelacanth that currently inhabits the deep ocean off Africa, not upstream freshwater rivers where amphibians originated; it has gone through various evolutionary processes and has become adapted to saltwater and seawater pressure. As an advanced evolutionary product, it now survives in the deep sea off the Comoro Islands and their vicinity without submitting to other organisms. The same can be said about the bonobo. Even if the bonobo has retained some characteristics that closely resemble the last common ancestor of the human and the African great apes, after the split between the human lineage, the genus Pan (the genus that includes the common chimpanzee, P. troglodytes, and the bonobo, P. paniscus), and the gorillas, all three lineages have followed separate evolutionary paths. So the chimpanzee and the bonobo, each of which has independently evolved since their last common ancestor split from the human ancestor about 7 million years ago, have never been the living fossils of the human ancestral species. It is the same as that our species is not the living fossil of the ancestral species of the chimpanzee or the bonobo.

After completing a year of lectures in biology, I became disappointed with the question that students asked me, Professor, the chimpanzee is really intelligent, isn’t it? If the chimpanzee continues to evolve, will it become like us? I realized that what I had wanted to convey had not been well communicated to them. Flipping the question around on them, it is the same as asking, If we continue to evolve, will we become like the chimpanzee or the bonobo?

Neither the chimpanzee nor the bonobo is a living fossil of the human, but if we accept that, what can we learn from the current state of the bonobo and the chimpanzee?

Chimpanzees, bonobos, and, of course, humans have inherited various characteristics from the last common ancestor. To understand what our common ancestor was like, it is necessary to conduct research comparing all the three species. This allows us to find our common denominator or common characteristics we inherited from our last common ancestor. The reasoning behind this is that if each of the three species has independently followed its evolutionary path and still possesses a suite of shared characteristics, our last common ancestor probably also had the same characteristics. But what if we find characteristics that only one or two of the three species possess? Each species might have independently or uniquely acquired those characteristics after the split from the common ancestor. Or, the common ancestor might have those characteristics, they might have been retained by only one or two species to the present day while they might have been lost in other species during the course of evolution.

As you can imagine, it is not easy to infer the characteristics of our last common ancestor by comparing modern species of humans, chimpanzees, and bonobos. Indeed, although the two great apes share many features that have been presumably inherited from the last common ancestor, they also possess greatly contrasting characteristics. It is hard to figure out what the last common ancestor of Pan was like, let alone the last common ancestor of Pan and Homo.

Both chimpanzees and bonobos live in groups of several dozen of individuals that can include multiple males and multiple females [3, 4]. In a group, sexual relations among males and females are promiscuous. Only female parents raise their offspring. They nurse them for more than 3 years after birth. Males spend their entire lifetime in their natal group, but females leave their mother’s group around puberty and transfer to a different group [5, 6]. These are common features shared by not only the chimpanzee and the bonobo but probably also by the ancestral species of humans.

While the two great ape species share similarities in above aspects, their sociality significantly differs [5, 7, 8]. In the chimpanzee, contests over dominance ranks among males are extremely fierce, while bonobo males do not appear to care about rank very much. In the chimpanzee, power struggles within a group may sometimes turn fatal, but such lethal behavior has never been observed in the bonobo [9]. Chimpanzees deploy various types of greeting behaviors that verify one another’s hierarchical ranks, but bonobos perform various types of sexual behaviors for greeting, without caring about rank [10]. In the chimpanzee, a male mounting a female from behind (like riding on a horseback) is a common form of heterosexual intercourse, but bonobo females prefer face-to-face sexual intercourse that permits looking at each other’s face [11]. Chimpanzee females become sexually receptive only during periods when there is a possibility of pregnancy, but female bonobos display sexual receptivity even during periods when they are pregnant or nursing when there is absolutely no possibility of conception [5, 12].

In the chimpanzee, relationships between groups are intensely hostile. In extreme cases, one group may annihilate the neighboring group [13–15]. However, intergroup relationships in the bonobo are relatively friendly. When two groups encounter each other, they may, at first, intimidate each other, but eventually, they mingle and feed together and can spend time together for a number of days [16–18]. In the chimpanzee, males predominantly dominate over females, but in the bonobo, females’ social ranks are equal to or higher than those of males [19–21]. While female chimpanzees have a strong tendency to live separately from each other, female bonobos gather in the center of the group and maintain intimate relationships, despite the fact that they are all strangers that have transferred from other groups [22]. Staying in the middle of the group keeps their superiority over males; sometimes females cooperatively drive away a male that instigates an aggressive action against a female [23]. Female bonobos lead a group’s movement [23], and more often