Orangutan

For other uses, see Orangutan (disambiguation).

Orangutans are great apes that live in the rainforests of Indonesia and Malaysia. Today they are found only in parts of Borneo and Sumatra. Long ago, during the Pleistocene, they lived across much of Southeast Asia and southern China. Scientists once thought orangutans were all one species in the genus Pongo. In 1996, they were split into two species: the Bornean orangutan (P. pygmaeus, with three subspecies) and the Sumatran orangutan (P. abelii). In 2017, a third species, the Tapanuli orangutan (P. tapanuliensis), was clearly identified. Orangutans are the only living members of the subfamily Ponginae. This group split off from the other great apes and humans, which include gorillas, chimpanzees, and humans, between about 19.3 and 15.7 million years ago.

Orangutans are the most arboreal of the great apes, which means they spend most of their time in trees. They have long arms, short legs, and reddish-brown hair. Adult males that are dominant grow cheek pads and make long calls that attract females and warn rivals to stay away. Orangutans are the most solitary of the great apes. They mostly form close bonds between mothers and their young. Fruit is the most important food for them, but they also eat leaves, bark, honey, insects, and bird eggs. They can live more than 30 years, both in the wild and in captivity.

Orangutans are among the smartest primates. They use a variety of sophisticated tools and build sleeping nests from branches and leaves each night. Scientists have studied their learning abilities a great deal, and different groups may have their own special ways of doing things. Primatologist Biruté Galdikas pioneered field studies of these apes. Orangutans have been kept in zoos and other facilities around the world since at least the early 1800s.

All three orangutan species are considered critically endangered, which means they are in very serious danger of disappearing. Human activities have caused their numbers and living areas to shrink greatly. Wild orangutans are threatened by poaching, habitat destruction, and deforestation for palm oil farming and logging. They are also affected by the illegal pet trade. Many conservation and rehabilitation groups work to help 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 two Malay words. Orang means 'person', and hutan means 'forest'. Malay speakers used the term for forest-dwelling humans. The first recorded Malay use of "orang-utan" for the ape came from a Western source. 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 doctor Jacobus Bontius. Some scholars think the word comes from the Banjarese form of Malay, but Old Malay is a more likely origin. Cribb and colleagues (2014) suggest that Bontius was describing humans with a serious health problem (most likely cretinism), and that Nicolaes Tulp misunderstood his use of the word.

The word was first recorded in English in 1693 by doctor John Bulwer as Orang-Outang. This spelling is still used in English, but it is now considered incorrect. The missing "h" in hutan suggests the term came into English through Portuguese. The name of the genus, Pongo, comes from Andrew Battel, an English sailor who was held prisoner by the Portuguese in Angola. He wrote about two "monsters" called Pongo and Engeco. Today, people believe he was describing gorillas. In the 18th century, the terms orangutan and pongo were used for all great apes. In 1799, French naturalist Bernard Germain de Lacépède used Pongo as the genus name. The word 'orangutan' in modern Malay and Indonesian was borrowed from English or Dutch in the 20th century.

See also: Orangutan–human last common ancestor

The orangutan was first described scientifically in 1758 by Carl Linnaeus in the Systema Naturae. Over time, it has been renamed and given new names. In 1827, French naturalist René Lesson described P. abelii. People suggested that the populations on the two islands were separate species. In 2001, P. abelii was confirmed as a full species, and three groups on Borneo were made into 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 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, mainland Southeast Asia, and South China. Their range shrank by the end of the Pleistocene, most likely because their forest homes became smaller during the Last Glacial Maximum.

Characteristics

Male and female orangutans look quite different. Females usually stand about 115 cm (45 in) tall and weigh about 37 kg (82 lb). Adult males stand about 137 cm (54 in) tall and weigh about 75 kg (165 lb). The tallest orangutan recorded was 180 cm (71 in). Compared to humans, they have long arms, and a male's arm span is about 2 m (6 ft 7 in). Their legs are short. Their long hair is reddish. It starts out bright orange and gets darker, turning maroon or chocolate, as they grow older. Their skin is grey-black, and adult males 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 curves inward and sticks out (prognathous). The brow ridge is less developed than in other great apes. Females and young orangutans have rounder skulls and thinner faces. Adult males have a large sagittal crest on top of the head, large cheek pads, throat pouches, and long canines (teeth). The throat pouches act as resonance chambers, which help them make long calls.

Orangutans have four long fingers and a much shorter opposable thumb. This helps them grip branches high in the trees. Their feet 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 than Bornean orangutans. They have paler, longer hair and a longer face. Tapanuli orangutans look more like Sumatran orangutans in body build and hair colour. However, 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. Fewer live in drier forests or high up on mountains. Their predators include tigers, clouded leopards and wild dogs. Orangutans can carry tiny living things inside them, such as nematodes of the genus Strongyloides and the ciliate Balantidium coli. They also use the plant Dracaena cantleyi as a balm. Most of their day is spent eating, resting and moving from place to place. At night, they build their nests.

Orangutans mainly eat fruit. 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, so they spend more time alone than other great apes. Females live in home ranges inside a male's range. Young orangutans disperse to set up their own ranges by age 11. They communicate with calls and gestures. Females care for their young, which cling to their mothers at first. Females usually have their first baby around age 15. Babies are born about nine months after mating. Orangutans may live over 30 years. Adults and young build nests to sleep in during the day or night. 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 primates other than humans. 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." This means one helps another, expecting to be helped back later. They were the first nonhuman species recorded doing this. In a 1997 study, two adult orangutans living in captivity were tested with the cooperative pulling paradigm. They got food by pulling an object together. Over 30 sessions, they worked faster as they learned to work together. An adult orangutan passed the mirror test, which shows self-awareness. A 2-year-old did not recognise itself in the mirror. Orangutans may also communicate about things that are not present. Mothers stay quiet when danger is near. Afterward, they make an alarm call to teach their young about the danger. Orangutans and other great apes make laughter-like sounds while wrestling, chasing in play, or being tickled. Orangutans can also learn new sounds. Bonnie, an orangutan at the US National Zoo, was recorded whistling after hearing a caretaker.

Orangutans make and use tools. Primatologist Biruté Galdikas saw tool use in groups that had once lived in captivity. Orangutans at Suaq Balimbing developed a set of tools for finding food. They used sticks to get insects out of tree hollows and other sticks to collect seeds from hard-shelled fruit. They changed their tools to suit each task. Orangutans have been seen using sticks to poke at catfish so the catfish jump 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. They suggested the differences are cultural. In Tuanan, Borneo, wild orangutans use leaves to make their kiss squeak sounds louder. This may deceive listeners into thinking they are bigger. In 2003, researchers compared tool use at six orangutan field sites. They found that each group used different tools. In a field observation in 2022, a male Sumatran orangutan known as Rakus chewed Fibraurea tinctoria vine leaves. He then applied the mashed plant to an open wound on his face. According to primatologists who watched him, the wound closed within five days. It 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. This was based on the guidelines of the Great Ape Project. These guidelines say that chimpanzees, bonobos, orangutans, and gorillas should not be used in animal experiments. In December 2014, a court in Argentina ruled that an orangutan named Sandra at the Buenos Aires Zoo should be moved to a sanctuary in Brazil. There she could have "partial or controlled freedom." Animal rights groups argued the ruling should apply to all captive animals. However, legal experts at Argentina's Federal Chamber of Criminal Cassatio decided it applied 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 made rules against these practices. 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 a strong supporter of orangutans and their rainforest home. That home 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. The group is named after anthropologist Louis Leakey.

Orangutans first appeared in Western stories in the 18th century. 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 asked for these acts to stop, because they believe the animals were treated badly. Starting in the 1960s, zoos focused more on education. Orangutan exhibits were designed to look more like their natural environment. Ken Allen, an orangutan at the San Diego Zoo, became world famous in the 1980s for his many escapes. He 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 protected by law in Malaysia and Indonesia. They are also listed under Appendix I by CITES, which bans trade in them without a license. Bornean orangutans live in fewer areas now. Their largest group lives in the forest near the Sabangau River, where the environment is in danger. Sumatran orangutans live mainly in the Leuser Ecosystem in northern Sumatra. Tapanuli orangutans live only in the Batang Toru forest.

Orangutans face many threats. These include poaching, deforestation, and loss of their homes from logging, mining, and fragmentation caused by roads. A major cause is the clearing of tropical forest to make palm oil plantations. Hunting, the illegal pet trade, and the bushmeat trade also harm them. Many groups work to rescue orangutans, care for them, and return them to the wild. The largest is the Borneo Orangutan Survival (BOS) Foundation, which was founded by Willie Smits. BOS runs the Nyaru Menteng Rehabilitation Program, which was started by Lone Drøscher Nielsen. In 2017, BOS rescued an albino orangutan from captivity in Kapuas Hulu. The orangutan was later named Alba. Other conservation centres include Tanjung Puting National Park, Sebangau National Park, Gunung Palung National Park, Bukit Baka Bukit Raya National Park, Gunung Leuser National Park, Bukit Lawang, and the Sepilok Orangutan Rehabilitation Centre. Some groups are based in other countries. These include the Frankfurt Zoological Society, Orangutan Foundation International, and the Australian Orangutan Project. The Orangutan Land Trust works with the palm oil industry. It aims to improve sustainability and to set up conservation areas for orangutans.