Bonobo
The bonobo, also historically called the pygmy chimpanzee, is an endangered great ape and one of the two species making up the genus Pan. While bonobos are today recognized as a distinct species, they were initially thought to be a subspecies of Pan troglodytes, because of the physical similarities between the two species. Taxonomically, members of the chimpanzee/bonobo subtribe Panina—composed entirely by the genus Pan—are collectively termed panins.
Bonobos are distinguished from common chimpanzees by relatively long limbs, pinker lips, a darker face, a tail-tuft through adulthood, and parted, longer hair on their heads. Some individuals have sparser, thin hair over parts of their bodies. The bonobo is found in a area within the Congo Basin of the Democratic Republic of the Congo, Central Africa. It is predominantly frugivorous, compared to the often highly omnivorous diets and hunting of small monkeys, duiker and other antelope exhibited by common chimpanzees. Bonobos inhabit primary and secondary forest, including seasonally inundated swamp forest. Because of political instability in the region, and the general timidity of bonobos, there has been relatively little field work done observing the species in its natural habitat.
Along with the common chimpanzee, the bonobo is the closest extant relative to humans. As the two species are not proficient swimmers, the natural formation of the Congo River possibly led to the isolation and speciation of the bonobo. Bonobos live south of the river, and thereby were separated from the ancestors of the common chimpanzee, which live north of the river. There are no concrete figures regarding population, but the estimate is between 29,500 and 50,000 individuals. The species is listed as Endangered on the IUCN Red List and is most threatened by habitat destruction, human population growth and movement, with commercial poaching being, by far, the most prominent threat. Bonobos typically live 40 years in captivity; their lifespan in the wild is unknown, but it is almost certainly much shorter.
Etymology
Formerly the bonobo was known as the "pygmy chimpanzee", despite the bonobo having a similar body size to the common chimpanzee. The name "pygmy" was given by the German zoologist Ernst Schwarz in 1929, who classified the species on the basis of a previously mislabeled bonobo cranium, noting its diminutive size compared to chimpanzee skulls.The name "bonobo" first appeared in 1954, when Austrian zoologist Eduard Paul Tratz and German biologist Heinz Heck proposed it as a new and separate generic term for pygmy chimpanzees. The name is thought to derive from a misspelling on a shipping crate from the town of Bolobo on the Congo River near the location from which the first bonobo specimens were collected in the 1920s.
In English the word is generally stressed on the second syllable, in both the US and UK, though sometimes it is instead stressed on the first syllable.
Taxonomy
The bonobo was first recognised as a distinct taxon in 1928 by German anatomist Ernst Schwarz, based on a skull in the Tervuren Museum in Belgium which had previously been classified as a juvenile chimpanzee. Schwarz published his findings in 1929, classifying the bonobo as a subspecies of chimpanzee, Pan satyrus paniscus. In 1933, American anatomist Harold Coolidge elevated it to species status. Major behavioural differences between bonobos and chimpanzees were first discussed in detail by Tratz and Heck in the early 1950s. Unaware of any taxonomic distinction with the common chimpanzee, American psychologist and primatologist Robert Yerkes had already noticed an unexpected major behavioural difference in the 1920s.Bonobos and chimpanzees are the two species which make up the genus Pan, and are the closest living relatives to humans.
Bonobos and common chimpanzees show remarkable evolutionary stasis in musculoskeletal anatomy since their split from humans 8 million years ago, with bonobos exhibiting no changes since diverging from common chimps ~2 million years ago, making them a better anatomical model for the last common ancestor of humans and chimps/bonobos.
Nonetheless, the exact timing of the Pan–''Homo last common ancestor is contentious, but DNA comparison suggests continual interbreeding between ancestral Pan and Homo groups, post-divergence, until about 4 million years ago. DNA evidence suggests the bonobo and common chimpanzee species diverged approximately 890,000–860,000 years ago following separation of these two populations possibly because of acidification and the spread of savannas at this time. Currently, these two species are separated by the Congo River, which had existed well before the divergence date, though ancestral Pan may have dispersed across the river using corridors which no longer exist. The first Pan fossils were reported in 2005 from the Middle Pleistocene of Kenya, alongside early Homo fossils.
According to A. Zihlman, bonobo body proportions closely resemble those of Australopithecus, leading evolutionary biologist Jeremy Griffith to suggest that bonobos may be a living example of our distant human ancestors. According to Australian anthropologists Gary Clark and Maciej Henneberg, human ancestors went through a bonobo-like phase featuring reduced aggression and associated anatomical changes, exemplified in Ardipithecus ramidus''.
The first official publication of the sequencing and assembly of the bonobo genome was released in June 2012. The genome of a female bonobo from Leipzig Zoo was deposited with the International Nucleotide Sequence Database Collaboration under the EMBL accession number AJFE01000000 after a previous analysis by the National Human Genome Research Institute confirmed that the bonobo genome is about 0.4% divergent from the chimpanzee genome.
Genetics and genomics
Relationships of bonobos to humans and other apes can be determined by comparing their genes or whole genomes. While the first bonobo genome was published in 2012, a high-quality reference genome became available only in 2021. The overall nucleotide divergence between chimpanzee and bonobo based on the latter is 0.421 ± 0.086% for autosomes and 0.311 ± 0.060% for the X chromosome. The reference genome predicts 22,366 full-length protein-coding genes and 9,066 noncoding genes, although cDNA sequencing confirmed only 20,478 protein-coding and 36,880 noncoding bonobo genes, similar to the number of genes annotated in the human genome. Overall, 206 and 1,576 protein-coding genes are part of gene families that contracted or expanded in the bonobo genome compared to the human genome, respectively, that is, these genes were lost or gained in the bonobo genome compared to humans.Hybrids
Researchers have found that both central and eastern chimpanzees share more genetic material with bonobos than other chimpanzee subspecies. It is believed that genetic admixture has occurred at least two times within the past 550,000 years. In modern times hybridization between bonobos and chimpanzees in the wild is prevented as populations are allopatric and kept isolated on different sides of the Congo river.Within captivity, hybrids between bonobos and chimpanzees have been recorded. Between 1990 and 1992, five pregnancies were conceived and studied between a male bonobo and two female chimpanzees. The two initial pregnancies were aborted because of environmental stressors. The following three pregnancies however led to the birth of three hybrid offspring.
A bonobo and chimpanzee hybrid called Tiby was also featured in the 2017 Swedish film The Square. This same male bonobo and female chimpanzee had several offspring.
Description
The bonobo is commonly considered to be more gracile than the common chimpanzee. Although large male chimpanzees can exceed any bonobo in bulk and weight, the two species broadly overlap in body size. Adult female bonobos are somewhat smaller than adult males. Body mass ranges from with an average weight of in males against an average of in females. The total length of bonobos is. Male bonobos average when standing upright, compared to in females. The bonobo's head is relatively smaller than that of the common chimpanzee with less prominent brow ridges above the eyes. It has a black face with pink lips, small ears, wide nostrils, and long hair on its head that forms a parting. Females have slightly more prominent breasts, in contrast to the flat breasts of other female apes, although not so prominent as those of humans. The bonobo also has a slim upper body, narrow shoulders, thin neck, and long legs when compared to the common chimpanzee.File:Bonobos Kanzi and Panbanisha with Sue Savage-Rumbaugh.jpg|thumb|left|Bonobos Kanzi and Panbanisha with Sue Savage-Rumbaugh and the outdoor symbols "keyboard"
Bonobos are both terrestrial and arboreal. Most ground locomotion is characterized by quadrupedal knuckle-walking. Bipedal walking has been recorded as less than 1% of terrestrial locomotion in the wild, a figure that decreased with habituation, while in captivity there is a wide variation. Bipedal walking in captivity, as a percentage of bipedal plus quadrupedal locomotion bouts, has been observed from 3.9% for spontaneous bouts to nearly 19% when abundant food is provided. These physical characteristics and its posture give the bonobo an appearance more closely resembling that of humans than the common chimpanzee does. The bonobo also has highly individuated facial features, as humans do, so that one individual may look significantly different from another, a characteristic adapted for visual facial recognition in social interaction.
Multivariate analysis has shown bonobos are more neotenised than the common chimpanzee, taking into account such features as the proportionately long torso length of the bonobo. Other researchers challenged this conclusion.