Orangutans are great apes of the genus Pongo; they are the largest living nonhuman primates after gorillas, and one of the most critically endangered. They live only on the islands of Borneo and Sumatra, in Southeast Asia. They are found over most of Borneo, but in Sumatra they are restricted to the northern quarter, with a few isolated populations some way down the west coast. The name is a corruption of orang hutan (“forest-living person”) and may originally have designated tribal people such as the Penan of Borneo or the Kubu of Sumatra, but it became commonly used in Europe to refer to any ape. Most indigenous peoples refer to them as mawas.
Orangutans have sparse reddish hair covering dark grey skin. The arms are longer, compared to the legs, than any other primate: the intermembral index (arm length as a percentage of leg length) varies between 135 and 150%. The face is strongly prognathous (the jaws jut forward); the profile varies from concave to nearly straight; the orbits are tall and oval, without supraorbital tori (thickened brow ridges); the forehead is round and ascends at about 60° behind and above the orbits; the braincase is short, high, and rounded. As in other great apes (gorillas and chimpanzees), the canine teeth are relatively long but thick in males and shorter and smaller in females, but unlike other great apes, the orangutan’s upper central incisors are expended and spade-shaped, while the lateral incisors are thin and pointed. The molar teeth are large and flat, with thick enamel that is minutely wrinkled. Fully grown male orangutans weigh from 80 to 91 kg, adult females less than half of this, from 33 to 45 kg.
Genetically, orangutans differ from gorillas, chimpanzees, and humans by about 3.1%, implying that their ancestors separated from them before they separated from each other; in other words, orangutans are the third most closely related ape to us. These phylogenetic relationships are recognized by placing them all in the family Hominidae, but in different subfamilies: orangutans belong by themselves in the subfamily Ponginae, while gorillas, chimpanzees, and humans belong in the subfamily Homininae.
Bornean and Sumatran orangutans are very different and are today placed in different species. The Sumatran orangutan (Pongo abelii) is taller and leaner in build, the hair is usually gingery in color (though there is some variation in this), and the face is covered in light downy hair and is an elongated oval shape. The Bornean orangutan (Pongo pygmaeus)is shorter and fatter, the hair is usually dark maroon, and the face is hairless and figure-8 shaped, with deep hollows under the cheeks. The chromosomes have characteristic differences. Molecular clock calculations suggest that they may have separated as much as 1.5 to 2 million years ago.
Orangutans are almost wholly arboreal—except, perhaps, for some old Bornean males—and largely solitary. This does not mean that they lack a social organization; on the contrary, their social relations are highly complex and reflect their prodigious cognitive skills, which seem to be barely, if at all, inferior to those of chimpanzees (like chimpanzees, some orangutans quickly learn to recognize themselves in mirrors). They feed mainly on fruit, falling back on figs during periods when fruit is scarce, and also eat leaves, bark (especially in Borneo), and insects (especially in Sumatra). In one study site, Suaq Balimbing in northern Sumatra, females occupy overlapping home ranges averaging 850 ha, whereas fully grown males have much larger ranges, about 2,500 ha, which overlap those of both females and other males. In Borneo, these home ranges appear to be generally smaller. Females may associate together temporarily, but males do their best to avoid each other. Males who are not fully grown have similarly large ranges, and avoid the full-grown males. There are also nomadic males who may wander from site to site looking either for food or for fertile females.
They are very slow breeders. Their gestation period is about 240 days, and they give birth to a single young who is dependant on its mother for years. Both sexes become sexually mature at about 8-10 years. The interval between live births is perhaps the longest of any mammal—at least 6 years, and as much as 8 years in some populations. They may need this time to learn the complexities of life in the rain forest. In captivity, they may live well over 50 years; in the wild, they certainly reach considerable ages, but exactly how long they may live is not known.
The big males have flanges of connective tissue at the sides of the face, beards and moustaches (longer in Sumatran orangutans), and large throat pouches (bigger in Bornean orangutans). With the aid of the throat pouch, a male makes a booming call, which alerts females and rival males alike to his presence. The females are attracted to the big-flanged males and mate with them at midcycle; the menstrual cycle averages 29 days long. The males who are not fully grown, but are sexually mature, try to mate with females who are, however, unwilling; their attempts have been described as “rape”; in Borneo, even flanged males may force copulations in this way, but this is very rare in Sumatra.
Two surprising discoveries have been made recently. First is that these unflanged males—at least in the Sumatran species—are not necessarily subadult; they may remain in that condition for years, perhaps for their whole lives. It has been proposed that it is a way of avoiding the stress of maturing fully when a flanged male is around. Second is that, at least in one study site in Sumatra, unflanged males sire as many offspring as the big flanged males, so it is obviously a very successful alternative reproductive strategy.
Different orangutan populations have different cultures, just as do different chimpanzee populations. All orangutans make an aggressive sound called a “kiss-squeak”; in just two populations, both in Borneo, an individual will hold a leaf to the mouth to amplify this sound. Only in the Suaq Balimbing population do orangutans use sticks to winkle out insects from tree holes. In one Borneo population it is customary to wipe sticky substances from the chin with a “napkin” of leaves. Each population is remarkably different and has built up its own culture over years or perhaps even centuries.
As recently as the Late Pleistocene, orangutans lived all over Sumatra, in Java, and on the mainland of Southeast Asia as far north as southern China. Today, they are crashing toward extinction. In historic times they are known to have inhabited only Malaysian Borneo (Sabah and Sarawak) and Indonesia. In Malaysia the numbers declined during the early 20th century but are today stable, if fairly low. The coming of democracy to Indonesia in the late 1990s was unfortunately accompanied by a breakdown of law and order, and illegal logging, forest fires, and clearing of land for oil palm plantations have destroyed much orangutan habitat, while hunting and the smuggling of young orangutans overseas have greatly increased. Although the situation is slowly coming under control, there will probably be very few orangutans remaining in five years’ time—perhaps none in at all in Sumatra. This will be a scientific, cultural, moral, and humanitarian tragedy.
Orce is a Spanish village famous for the controversy regarding the supposed finding of the oldest Eurasian hominid: the Orce man. Orce is near the Venta Micena paleontological site in the Guadix-Baza basin, Granada province, Spain. In 1982, a small cranial fragment was found in the Venta Micena excavation quarry and was published in 1983 as Homo sp. by Josep Gibert, Jordi Agusti, and Salvador Moya Sola. They claimed that this fossil, unearthed from sediments 1.8 million years old, constituted the oldest hominid found in Eurasia and belonged to Homo erectus or even Homo habilis. Once the fossil was cleaned, in the inner face a prominent crest appeared, and the controversy began. The prestigious French paleoanthropologists, Henry and Marie Antoinette de Lumley, retracted their support of the hominid attribution. Agusti and Moya Sola published a paper in 1987 concluding that the suture and the crest made impossible the attribution to Homo and the fossil was reattributed to Equus. Nevertheless, Gibert decided to maintain his attribution to Homo and began a controversial search for evidence and support.
The fragmentary fossil, popularly named the “biscuit,” given its small size and rounded form, was exhaustively analyzed. Domenec Campillo concluded, based on the contradictory morphology, that it belonged to an infant of the genera Homo. Enrique Garcia Olivares also concluded, based on immunological analyses, that the fossil belonged to a hominid, but it was suspicious that a fossil so old contained such high quantities of human albumin. Paul Palmqvist studied the cranial suture using fractal analysis and also concluded that the fossil could have belonged to the genus Homo. However, Palmqvist soon realized that the oversimplified suture sent by Gibert was not real, accused him of fraud, and published another paper in the Journal of Human Evolution, reevaluating the evidence and concluding that the fossil may have belonged to a 3- to 5-month-old horse. The details regarding this controversy were reported in 1998 by Eustoquio Molina in the journal El Esceptico, concluding that this could be a case of pathological science.
The controversy was magnified by the mass media, where Gibert looked for support, making many sensational claims. Three outstanding Spanish paleontologists replied in a newspaper article, criticizing the Gibert methodology. As was stated long ago by David Hume, extraordinary claims demand extraordinary evidence (Occam’s razor), however the evidence found by Gibert and his colleagues is not extraordinary but very suspicious and controversial. Consequently, the most plausible attribution of the fragmentary fossil is to Equus, which is very abundant in the site, although based on a recent reinterpretation of the anatomical evidence by Bienvenido Martinez Navarro, it could be attributed to a ruminant, which is also frequent in the site. Nevertheless, Gibert still maintains the hominid attribution in his controversial book, El Hombre de Orce: Los Hominidos que Llegaron del Sur (2004). At present, few scientists believe Gibert’s sensational claims, but he still has the support of his friend Campillo, who published another controversial book, El Crâneo Infantil de Orce: El Hominido Mas Antiguo de Eurasia (2002).
The oldest fossil hominid remains in Eurasia cannot be the controversial fossil fragment from the Venta Micena site, which is not considered human. At present, the oldest human remains in Spain are those of Homo antecessor from the Trinchera Dolina site (Atapuerca) dated at 0.78 million years. Furthermore, the oldest hominid evidence is the lithic industry that has been recently found at the Sima del Elefante site (Atapuerca) and Barranco Leon-5 and Fuente Nueva-3 sites (Orce). This evidence is dated at about 1 to 1.3 million years, having been found just below Jaramillo in the Matuyama magnetochron.
- Agusti, J., & Moyà-Solâ, S. (1987). Sobre la identidad del fragmento atribuido a Homo sp. de Venta Micena (Orce, Granada). Estudios Geolôgicos, 45, 535-538.
- Gibert, J., Campillo, D., Arqués, J. M., Garcia-Olivares, E., Borja, C., & Lowenstein, J. M. (1997). Hominid status of the Orce cranial fragment reasserted. Journal of Human Evolution, 30, 1-15.
- Molina, E. (1998). El polemico fôsil de Orce: “falta de rigor o fraude” El Escéptico, 1, 73-76.
- Palmqvist, P. (1997). A critical re-evaluation of the evidence for the presence of hominids in Lower Pleistocene times at Venta Micena, Southern Spain. Journal of Human Evolution, 33, 83-89.