Orangutan

For other uses, see Orangutan (disambiguation).

Orangutans are great apes native to the rainforests of Indonesia and Malaysia. They are now found only in parts of Borneo and Sumatra, but during the Pleistocene they ranged throughout Southeast Asia and South China. Orangutans were originally considered to be one species in the genus Pongo. In 1996, they were divided into two species: the Bornean orangutan (P. pygmaeus, with three subspecies) and the Sumatran orangutan (P. abelii). A third species, the Tapanuli orangutan (P. tapanuliensis), was identified definitively in 2017. Orangutans are the only surviving members of the subfamily Ponginae, which diverged genetically from the other hominids (gorillas, chimpanzees, and humans) between 19.3 and 15.7 million years ago.

The most arboreal of the great apes, orangutans spend most of their time in trees. They have long arms, short legs, and reddish-brown hair covering their bodies. Adult males that are dominant develop distinctive cheek pads and make long calls that attract females and intimidate rivals. Orangutans are the most solitary of the great apes, and their social bonds occur mainly between mothers and their young. Fruit is the most important part of their diet, but they also eat leaves, bark, honey, insects and bird eggs. They can live over 30 years, both in the wild and in captivity.

Orangutans are among the most intelligent primates. They use a variety of sophisticated tools and build elaborate sleeping nests each night from branches and leaves. Scientists have studied their learning abilities extensively, and there may be distinctive cultures within populations. Field studies of the apes were pioneered by primatologist Biruté Galdikas, and orangutans have been kept in captive facilities around the world since at least the early 19th century.

All three orangutan species are considered critically endangered. Human activities have caused severe declines in their populations and ranges. Threats to wild orangutans include poaching (for bushmeat and as revenge for eating crops), habitat destruction and deforestation (for palm oil farming and logging), and the illegal pet trade. Several conservation and rehabilitation organisations are dedicated to helping orangutans survive in the wild.

Etymology

Most Western sources say the name "orangutan" (also written orang-utan, orang utan, orangutang, and ourang-outang) comes from the Malay words orang, meaning 'person', and hutan, meaning 'forest'. Malay speakers used the term for forest-dwelling humans, and the first recorded Malay use of "orang-utan" for the ape was a Western term. Some evidence suggests the term may have been used for apes in premodern Old Malay. The first printed use of the word for the apes in Western sources is in the 1631 book of Dutch physician Jacobus Bontius. Some scholars think the word comes from the Banjarese variety of Malay, but Old Malay is a more likely origin. Cribb and colleagues (2014) suggest that Bontius was describing humans with a serious medical condition (most likely cretinism), and that Nicolaes Tulp misunderstood his use of the word.

The word was first recorded in English in 1693 by physician John Bulwer as Orang-Outang. This spelling is still used in English but is now regarded as incorrect. The loss of the "h" in hutan suggests the term entered English through Portuguese. The name of the genus, Pongo, comes from Andrew Battel, an English sailor held prisoner by the Portuguese in Angola, who described two "monsters" called Pongo and Engeco. He is now believed to have been describing gorillas. In the 18th century, the terms orangutan and pongo were used for all great apes, and French naturalist Bernard Germain de Lacépède used Pongo as the genus name in 1799. The word 'orangutan' in modern Malay and Indonesian was borrowed from English or Dutch in the 20th century.

The orangutan was first described scientifically in 1758 by Carl Linnaeus in the Systema Naturae. It has been renamed and given new names over time. In 1827, a French naturalist, René Lesson, described P. abelii, and the populations on the two islands were suggested to be separate species. In 2001, P. abelii was confirmed as a full species, and three groups on Borneo were made subspecies. A third species, P. tapanuliensis, was described in 2017 from Sumatra, south of Lake Toba. Surprisingly, it is more closely related to the Bornean species than to the other Sumatran species.

The Sumatran orangutan was the third great ape to have its genome sequenced, after humans and chimpanzees. The Bornean species was sequenced later. Orangutans have 48 diploid chromosomes, while humans which have 46. Based on molecular evidence, orangutans split from the African great ape line about 19.3 to 15.7 million years ago. Their ancestors likely travelled from mainland Asia to Sumatra and Borneo when land bridges connected the islands during recent glacial periods. The three living species are the only living members of the subfamily Ponginae. Fossils of extinct relatives, such as Gigantopithecus, have been found in Asia. During the Pleistocene, orangutans lived across Sundaland and mainland Southeast Asia and South China. Their range shrank by the end of the Pleistocene, most likely because forest habitat was reduced during the Last Glacial Maximum.

Characteristics

Male and female orangutans look quite different. Females usually stand 115 cm (45 in) tall and weigh about 37 kg (82 lb). Adult males stand 137 cm (54 in) tall and weigh 75 kg (165 lb), and the tallest orangutan recorded was 180 cm (71 in). Compared to humans, they have long arms, with a male's arm span of about 2 m (6 ft 7 in), and short legs. Their long hair is reddish, starts out bright orange, and darkens to maroon or chocolate with age. Their skin is grey-black, and males' faces can grow a beard. Orangutans have small ears and noses, and their ears have no lobes. The average endocranial volume is 397 cm³. The face is curved inward and prognathous, and the brow ridge is underdeveloped compared to other great apes. Females and young orangutans have rounder skulls and thinner faces. Adult males have a prominent sagittal crest, large cheek pads, throat pouches, and long canines. The throat pouches act as resonance chambers for making long calls.

Orangutans have four long fingers and a much shorter opposable thumb, which helps them grip branches high in the trees. Their feet also have four long toes and an opposable big toe, so their feet work a bit like hands. They move through the trees by climbing and suspension, and they rarely come down to the ground. Unlike African apes, they are not true knuckle-walkers. Instead, they bend their fingers and walk on the sides of their hands and feet. Sumatran orangutans are more slender, with paler and longer hair and a longer face than Bornean orangutans. Tapanuli orangutans look more like Sumatran orangutans in body build and hair colour, but they have shaggier hair, smaller skulls, and flatter faces than the other two species.

Ecology and behaviour

Orangutans spend most of their time in trees, in tropical rainforest, especially lowland dipterocarp and old secondary forest. They are more common near rivers, in freshwater and peat swamp forest, and fewer live in drier forests or at higher elevations. Their predators include tigers, clouded leopards and wild dogs. Common parasites include nematodes of the genus Strongyloides and the ciliate Balantidium coli. Orangutans also use the plant Dracaena cantleyi as a balm. Most of their day is spent feeding, resting and travelling, and at night they prepare their nests.

Orangutans are mainly fruit-eaters, and they also eat leaves, bark, honey and small animals such as slow lorises. Some eat soil, which is called geophagy. Orangutans are mostly solitary but social, living more alone than other great apes. Females live in home ranges inside a male's range, and young orangutans disperse to set up their own ranges by age 11. They communicate with calls and gestures. Females care for the young, which cling to their mothers at first. Females usually give birth around age 15, and young are born about nine months after mating. Orangutans may live over 30 years. Adults and young build nests for day or night use, and young orangutans learn this by watching their mothers.

Further information: Primate cognition

See also: Great ape language

Main articles: Great ape personhood, Great Ape Project, and Great ape research ban

Orangutans are among the most intelligent non-human primates. Experiments suggest they can track the displacement of objects both visible and hidden. At Zoo Atlanta, two Sumatran orangutans play games on a touch-screen computer. A 2008 study of two orangutans at the Leipzig Zoo showed they may practise "calculated reciprocity," where one helps another expecting to be paid back. They were the first nonhuman species documented to do this. In a 1997 study, two captive adult orangutans were tested with the cooperative pulling paradigm. They got food by pulling an object, and they worked faster over 30 sessions as they learned to coordinate. An adult orangutan passed the mirror test, which indicates self-awareness, while a 2-year-old did not show self-recognition. Orangutans may also communicate about things that are not present. Mothers stay silent when a threat is near, then give an alarm call afterward to teach their young about the danger. Orangutans and other great apes make laughter-like sounds during wrestling, play chasing, or tickling. Orangutans can also learn new sounds, and Bonnie, an orangutan at the US National Zoo, was recorded whistling after hearing a caretaker.

Orangutans make and use tools. Primatologist Biruté Galdikas observed tool use in ex-captive populations. Orangutans at Suaq Balimbing developed a tool kit for finding food, including sticks for getting insects out of tree hollows and sticks for harvesting seeds from hard-husked fruit. They adjusted their tools to the task. Orangutans have been seen using sticks to poke at catfish so the catfish leap out of the water. When building a nest, they seem able to tell which branches will hold their weight. Carel P. van Schaik and biological anthropologist Cheryl D. Knott found that Suaq Balimbing orangutans used these tools more often than other wild orangutans, and they suggested the differences are cultural. In Tuanan, Borneo, wild orangutans use leaves to amplify the kiss squeak sounds they make, which may deceive listeners into thinking they are larger. In 2003, researchers compared tool use across six orangutan field sites and found each population used different tools. In a field observation in 2022, a male Sumatran orangutan known as Rakus chewed Fibraurea tinctoria vine leaves and applied the mashed plant to an open wound on his face. According to primatologists observing him, the wound closed within five days and had healed within a few weeks, leaving only a small scar. In June 2008, Spain became the first country to recognise the rights of some non-human great apes, based on the guidelines of the Great Ape Project. These guidelines say that chimpanzees, bonobos, orangutans, and gorillas are not to be used for animal experiments. In December 2014, a court in Argentina ruled that an orangutan named Sandra at the Buenos Aires Zoo must be moved to a sanctuary in Brazil to provide her "partial or controlled freedom." Animal rights groups argued the ruling should apply to all captive species, but legal specialists at Argentina's Federal Chamber of Criminal Cassatio considered it applicable only to non-human hominids.

Orangutans and humans

Orangutans have been known to the native people of Sumatra and Borneo for thousands of years. Some communities hunted them for food and decoration, while others placed taboos on such practices. Some folk tales involve orangutans mating with and kidnapping humans. Europeans became aware of the orangutan in the 17th century. In 1779, Dutch anatomist Petrus Camper gave the first scientific description of the orangutan. Little was known about their behaviour until the field studies of Biruté Galdikas. She arrived in Borneo in 1971 and settled at a site in Tanjung Puting. She later became an outspoken advocate for orangutans and their rainforest home, which is being harmed by loggers, palm oil plantations, gold miners, and unnatural forest fires. Galdikas is considered one of Leakey's Angels, along with Jane Goodall and Dian Fossey, a group named after anthropologist Louis Leakey.

Orangutans first appeared in Western fiction in the 18th century, and writers have used them to comment on human society. In Thomas Love Peacock's 1817 novel Melincourt, an orangutan named Sir Oran Haut Ton becomes a candidate for Member of Parliament. By the early 19th century, orangutans were also kept in captivity. The London Zoo housed a female orangutan named Jenny, who learned to drink tea and met Charles Darwin. Zoos and circuses in the Western world used orangutans and other simians for entertainment. Animal rights groups have urged a stop to such acts, considering them abusive. Starting in the 1960s, zoos focused more on education, and orangutan exhibits were designed to resemble their natural environment. Ken Allen, an orangutan at the San Diego Zoo, became world famous in the 1980s for his many escapes and was nicknamed "the hairy Houdini".

Conservation

Main article: Endangerment of orangutans

All three orangutan species are critically endangered on the IUCN Red List of mammals. They are legally protected in Malaysia and Indonesia, and are listed under Appendix I by CITES, which prohibits their unlicensed trade. Bornean orangutans are spread across fewer areas, and their largest remaining group lives in the forest around the Sabangau River, where the environment is at risk. Sumatran orangutans live mainly in the Leuser Ecosystem in northern Sumatra, and Tapanuli orangutans live only in the Batang Toru forest.