The bonobo (Pan paniscus), also known as the pygmy chimpanzee, is an endangered great ape and one of two species in the genus Pan, the other being the common chimpanzee (Pan troglodytes). At first, bonobos were thought to be a type of common chimpanzee because of their similar appearance. However, they are now recognized as a separate species. All members of the chimpanzee and bonobo group, called Panina, belong to the genus Pan and are referred to as panins.

Bonobos differ from common chimpanzees in several ways. They have longer limbs, pinker lips, darker faces, and a tuft of hair on their tails that lasts into adulthood. Their head hair is longer and often parted. Some bonobos have thin hair on parts of their bodies. In captivity, bonobos usually live about 40 years, but their lifespan in the wild is likely much shorter. They live in the Congo Basin of the Democratic Republic of the Congo, Central Africa, in an area covering about 500,000 square kilometers. Bonobos mainly eat fruit, unlike common chimpanzees, which eat a wide variety of foods, including small monkeys, deer, and antelope. They live in both primary and secondary forests, including forests that flood seasonally. Due to political instability and the shy nature of bonobos, scientists have studied them less in their natural habitat.

Bonobos are the closest living relatives to humans, along with common chimpanzees. Because both species cannot swim well, the formation of the Congo River about 1.5 to 2 million years ago may have separated bonobos from common chimpanzees. Bonobos live south of the river, while common chimpanzees live north of it. Scientists estimate there are between 29,500 and 50,000 bonobos. The species is listed as Endangered on the IUCN Red List. The biggest threats to bonobos include habitat loss, human population growth, political conflict, and hunting for trade.

Etymology

The bonobo was once called the "pygmy chimpanzee," even though it is about the same size as the common chimpanzee. The name "pygmy" was given in 1929 by German zoologist Ernst Schwarz. He named the species based on a bonobo skull that had been incorrectly labeled, noting that it was smaller than chimpanzee skulls.

The name "bonobo" was first used in 1954 by Austrian zoologist Eduard Paul Tratz and German biologist Heinz Heck. They introduced it as a new and separate name for pygmy chimpanzees. The name likely comes from a mistake on a shipping crate labeled "Bolobo," a town near the Congo River where the first bonobo specimens were collected in the 1920s.

In English, the word "bonobo" is usually pronounced with the stress on the second syllable in both the United States and the United Kingdom. Sometimes, it is also stressed on the first syllable.

Taxonomy

The bonobo was first recognized as a separate group in 1928 by German anatomist Ernst Schwarz. He studied a skull in the Tervuren Museum in Belgium, which had earlier been thought to belong to a young chimpanzee (Pan troglodytes). Schwarz shared his findings in 1929, classifying the bonobo as a subspecies of chimpanzee, named Pan satyrus paniscus. In 1933, American anatomist Harold Coolidge classified the bonobo as a full species. Differences in behavior between bonobos and chimpanzees were first described in detail by Tratz and Heck in the early 1950s. At the same time, American psychologist and primatologist Robert Yerkes had already observed a major behavioral difference between bonobos and chimpanzees in the 1920s, though he was unaware of their separate classification.

Bonobos and chimpanzees are the two species in the genus Pan and are the closest living relatives to humans (Homo sapiens).

Since their split from humans 8 million years ago, bonobos and chimpanzees have shown little change in their musculoskeletal anatomy. Bonobos have not changed since they separated from common chimpanzees about 2 million years ago, making them a better model for studying the last common ancestor of humans and chimpanzees/bonobos.

However, the exact time when humans and the genus Pan shared a common ancestor is still debated. DNA studies suggest that groups of early Pan and Homo may have interbred after their split, until about 4 million years ago. DNA evidence also shows that bonobos and common chimpanzees split into separate species around 890,000–860,000 years ago. This split may have been caused by changes in the environment, such as the spread of savannas and increased acidity. Today, bonobos and chimpanzees are separated by the Congo River, which existed long before their split. Early Pan fossils were found in Kenya in 2005, from the Middle Pleistocene era, alongside early Homo fossils.

According to A. Zihlman, bonobos have body proportions similar to those of Australopithecus. This led evolutionary biologist Jeremy Griffith to suggest that bonobos may resemble early human ancestors. Australian anthropologists Gary Clark and Maciej Henneberg proposed that human ancestors may have passed through a bonobo-like stage, characterized by less aggression and specific anatomical changes, as seen in the fossil species Ardipithecus ramidus.

The first official publication of the bonobo genome was released in June 2012. The genome of a female bonobo from Leipzig Zoo was shared with scientific databases under the EMBL accession number AJFE01000000. Earlier research confirmed that the bonobo genome differs from the chimpanzee genome by about 0.4%.

The relationship between bonobos, humans, and other apes can be studied by comparing their genes or entire genomes. The first bonobo genome was published in 2012, but a high-quality reference genome became available in 2021. Based on this genome, the difference between chimpanzee and bonobo DNA is about 0.421% for autosomes and 0.311% for the X chromosome. The genome predicts 22,366 full-length protein-coding genes and 9,066 noncoding genes. However, cDNA sequencing confirmed 20,478 protein-coding genes and 36,880 noncoding genes, similar to the number of genes in the human genome. Compared to humans, the bonobo genome has 206 genes that were lost and 1,576 genes that were gained.

Studies show that central chimpanzees (Pan troglodytes troglodytes) and eastern chimpanzees (Pan troglodytes schweinfurthii) share more genetic material with bonobos than other chimpanzee subspecies. Scientists believe that genetic mixing occurred at least twice in the past 550,000 years. Today, bonobos and chimpanzees do not interbreed in the wild because they live in separate areas, divided by the Congo River.

In captivity, hybrids between bonobos and chimpanzees have been recorded. Between 1990 and 1992, five pregnancies occurred between a male bonobo and two female chimpanzees. The first two pregnancies ended due to environmental stress. The next three pregnancies resulted in the birth of three hybrid offspring.

A bonobo and chimpanzee hybrid named Tiby was featured in the 2017 Swedish film The Square. This same male bonobo and female chimpanzee had several offspring.

Description

The bonobo is often described as more slender than the common chimpanzee. While large male chimpanzees may be heavier than bonobos, the two species have similar body sizes overall. Adult female bonobos are slightly smaller than adult males. Bonobos weigh between 34 and 60 kilograms (75 to 132 pounds), with males averaging 45 kilograms (99 pounds) and females averaging 33 kilograms (73 pounds). The total length of a bonobo, measured from the nose to the rump while on all fours, is 70 to 83 centimeters (28 to 33 inches). When standing upright, male bonobos average 119 centimeters (3.90 feet), while females average 111 centimeters (3.64 feet). Bonobos have smaller heads and less pronounced brow ridges compared to chimpanzees. Their faces are black with pink lips, small ears, wide nostrils, and long hair that splits in the middle on their heads. Female bonobos have slightly more noticeable breasts than other female apes, but not as much as humans. Bonobos also have slim bodies, narrow shoulders, thin necks, and long legs compared to chimpanzees.

Bonobos live both on the ground and in trees. Most of their movement on the ground involves walking on all fours with their knuckles touching the ground. Walking on two legs is rare in the wild, making up less than 1% of their ground movement. This percentage may decrease when bonobos become used to humans. In captivity, bonobos walk on two legs more often, with observations ranging from 3.9% for spontaneous movements to nearly 19% when food is plentiful. These physical traits and posture make bonobos appear more similar to humans than chimpanzees. Bonobos also have distinct facial features, like humans, allowing individuals to look very different from one another. This helps them recognize each other during social interactions.

Studies using multivariate analysis suggest bonobos have more juvenile features than chimpanzees, such as a longer torso. However, some researchers disagree with this conclusion.

Behaviour

Primatologist Frans de Waal explains that bonobos show traits like altruism, compassion, empathy, kindness, patience, and sensitivity. He describes bonobo society as a matriarchy, meaning females hold significant power. Scientists who study bonobos in the wild have observed a wide range of behaviors, including aggression and frequent sexual activity, similar to chimpanzees. However, bonobos engage in sexual behavior more often across different relationships. Research by Takeshi Furuichi highlights that female bonobos spend more time in estrus (a reproductive phase) than female chimpanzees, emphasizing the role of female sexuality in their social bonds.

Some scientists argue that de Waal’s findings may only reflect captive bonobos, suggesting wild bonobos might be more aggressive like chimpanzees. De Waal counters that differences in behavior between bonobos and chimpanzees in captivity are meaningful, as they eliminate environmental influences. Even under the same conditions, the two species behave differently. A 2014 study found bonobos to be less aggressive than chimpanzees, especially eastern chimpanzees. Researchers noted that western chimpanzees and bonobos are more peaceful due to ecological factors. However, bonobos warn each other of danger less effectively than chimpanzees in similar situations.

In April 2024, biologists reported that bonobos may be more aggressive than previously believed. A 2025 study found that bonobos can recognize when humans lack knowledge, supporting the idea that bonobos and chimpanzees, like humans, may have a theory of mind (the ability to understand others’ thoughts).

Bonobos are unique among apes for their matriarchal social structure, where females and males share power. Unlike other apes, bonobos do not claim specific territories, and their communities move across large areas. Because food is spread out and females travel frequently, males gain no advantage by forming male alliances or defending a home range. Female bonobos have sharper canines than female chimpanzees, contributing to their influence. While males dominate females in one-on-one interactions, groups of bonded females may be equally powerful or even dominate males, sometimes forcing males to mate with them.

At the top of the hierarchy is a group of high-ranking females and males led by an experienced female matriarch who makes decisions for the group. Female bonobos earn status through experience, age, and alliances with other females. High-ranking females protect immigrant females from male harassment. While bonobos are often called matriarchal, some males can achieve high ranks and work with the dominant female. These males may even rank above other males and some females. Certain males alert the group to threats, such as pythons, leopards, or eagles.

Aggressive interactions between males and females are rare, and males are gentle with infants and juveniles. A male’s status depends on his mother’s status, and the mother-son bond remains strong throughout life. While hierarchies exist, rank is less important than in other primate societies. Bonobos are not territorial and often have friendly relationships with other groups. They share food with unrelated individuals. Bonobos retain infantile traits (paedomorphism), which reduces aggression and allows them to interact peacefully with unfamiliar bonobos.

Male bonobos form long-term friendships with females, and females prefer to mate with males who are kind and respectful. Because females can use alliances to avoid aggressive males, they select mates at their own pace. Aging bonobos become more irritable, and both sexes show similar levels of aggression. Bonobos live in a society where females move to new communities, while males stay in their birth group. Some males may join new groups, and females with powerful mothers may remain in their birth clan.

Alliances between males are weak, but females form strong bonds with each other. Males and females sometimes work together, such as during hunts. A male bonobo once adopted his orphaned infant brother. A mother may support her grown son in conflicts, helping him gain better relationships with females and increasing her chances of having grandchildren through him. She may even physically intervene to prevent other males from mating with certain females. While mothers help their sons, some males without mothers can still dominate others.

Female bonobos have also cared for infants from other groups. Bonobos rarely kill each other and are less violent than chimpanzees, but aggression still occurs. Although females dominate males and choose mates who are not aggressive, competition among males is intense. High-ranking males mate more often than low-ranking ones. Male bonobos are larger than females, and because they do not form alliances, they fight fiercely for access to females. Males may injure each other, losing fingers, eyes, or ears. Injuries can also occur when males threaten high-ranking females and are attacked by groups of females.

Because female bonobos mate with many males, males cannot be certain which offspring are theirs. As a result, mothers provide all parental care. Bonobos are less promiscuous than chimpanzees, and high-ranking males have more mating success. Unlike chimpanzees, where males can force females to mate, female bonobos can refuse unwanted males, an advantage from their female-female bonds. They often choose to mate with higher-ranking males.

Bonobo groups change size frequently, following a fission-fusion pattern. A group of about 100 bonobos may split into smaller groups during the day to search for food and reunite at night to sleep in nests.

Distribution and habitat

Bonobos are found only in the humid forests of the Democratic Republic of Congo, south of the Congo River and north of the Kasai River, which is a river that flows into the Congo. In 1927, Ernst Schwarz published a paper titled "Le Chimpanzé de la Rive Gauche du Congo," which announced his discovery of bonobos. Some people have linked the Parisian Left Bank to the left side of the Congo River, comparing the bohemian culture in Paris to the unique behavior of bonobos. The ranges of bonobos and chimpanzees are divided by the Congo River, with bonobos living to the south of the river and chimpanzees to the north.

Ecological role

In the Congo tropical rainforest, most plants rely on animals to help them reproduce and spread their seeds. Bonobos are the second-largest fruit-eating animals in this area, after elephants. Each bonobo is estimated to eat and spread about nine tons of seeds from more than 91 types of plants, including lianas, grasses, trees, and shrubs. These seeds pass through a bonobo’s digestive system for about 24 hours and can travel several kilometers (average 1.3 km; maximum 4.5 km) before being excreted in their feces. The seeds remain healthy and grow faster than seeds that are not passed through an animal’s body. After being spread by bonobos, some seeds have better survival rates when dung beetles (Scarabaeidae) help move them further.

Some plants, like Dialium, need bonobos to trigger the germination of their seeds, which are naturally dormant. Studies show that bonobos’ behavior influences the structure of plant populations. Most plants that depend on animals for seed spread cannot grow without this process, and the even distribution of trees suggests a strong connection to their dispersal agents. Few species can replace bonobos in spreading seeds, just as bonobos cannot replace elephants in this role. There is little overlap in the roles of fruit-eating mammals in the Congo, which are heavily hunted and at risk of local extinction. The loss of animals, known as defaunation, leads to the "empty forest syndrome," a major concern for conservation. The disappearance of bonobos, which spread seeds from 40% of tree species in these forests, or 11.6 million seeds over a bonobo’s lifetime, would harm the health of the Congo rainforest.

Conservation status

The IUCN Red List lists bonobos as an endangered species. Estimates suggest there are between 29,500 and 50,000 bonobos living today. Major threats to their survival include losing their habitat and being hunted for bushmeat. Hunting increased greatly during the first and second Congo Wars in the Democratic Republic of Congo because armed groups, even in protected areas like Salonga National Park, often hunted bonobos and other animals. This trend is part of a larger problem affecting many ape species.

Bonobos live in areas where people also live, so conservation efforts depend on the help of local communities. In the Cuvette Centrale region, where bonobos are found, some people resist creating national parks because past park projects forced indigenous communities from their homes. In Salonga National Park, no local people are involved in conservation, and surveys since 2000 show that bonobos, African forest elephants, okapis, and other animals have suffered greatly due to poaching and the bushmeat trade. In contrast, some areas without park borders have thriving bonobo populations because local traditions include rules against killing bonobos or other animals.

During the wars in the 1990s, researchers and international groups left the bonobo habitat. In 2002, the Bonobo Conservation Initiative started the Bonobo Peace Forest Project with support from Conservation International and local groups. This project works with communities to create protected areas managed by local people. This model, led by DRC organizations and communities, has helped protect over 50,000 square miles (130,000 km²) of bonobo habitat. Amy Parish, who leads the project, says it is a model for conservation in the 21st century.

The port town of Basankusu is located on the Lulonga River, where the Lopori and Maringa Rivers meet. It is a key location for transporting goods to cities like Mbandaka and Kinshasa. Because Basankusu is near the Lopori Basin and Lomako River—areas where bonobos live—conservation efforts use the town as a base.

In 1995, the Zoological Society of Milwaukee (ZSM), with help from scientists worldwide, published the Action Plan for Pan paniscus. This report gathered data from 20 years of research on bonobo populations and outlined steps to protect them. The plan guides conservation efforts for scientists, governments, and donors.

Following the Action Plan, the ZSM started the Bonobo and Congo Biodiversity Initiative. This program focuses on protecting habitats, training Congolese people, monitoring wildlife, and educating communities. The ZSM has worked with local researchers to survey Salonga National Park and improve park protection. Over time, the ZSM has also helped local people by building schools, providing medical supplies, and starting agriculture projects to reduce reliance on hunting.

With support from the United Nations, USAID, the U.S. Embassy, the World Wildlife Fund, and others, the ZSM has worked to:
– Survey bonobo populations and their habitats to find ways to protect them
– Create measures to stop poaching in Salonga National Park, a UN World Heritage Site
– Train Congolese people in education, agriculture, and jobs so they can help protect bonobos
– Develop small-scale conservation methods that can be used across Congo

In 2003, the U.S. government gave $54 million to the Congo Basin Forest Partnership. This funding has brought international groups to the region to help protect bonobos. While this effort may improve bonobo survival, success will depend on involving local and indigenous communities more fully.

Bonobo numbers are believed to have dropped sharply in the last 30 years, though surveys are difficult in war-torn areas. Estimates suggest between 50,000 and 60,000 bonobos remain, according to the World Wildlife Fund.

Groups like the World Wide Fund for Nature and the African Wildlife Foundation have raised awareness about the bonobo’s risk of extinction. Some suggest creating reserves in more stable regions or on islands in places like Indonesia. More people are now learning about bonobos, and even non-scientific websites have started groups to collect donations for their conservation.

In human culture

World Bonobo Day is celebrated on February 14, which is also known as Valentine's Day. This day was created in 2017 by the African Wildlife Foundation.