Orangutan (English spelling)

Orangutans are mammals of the order Primates and family Crenata. The name orangutan comes from the Malay word meaning "forest man" and is also known as Crenata. Together with the gibbons, they form the Asian apes, and together with three species of African apes, the great apes. Extant species are found on the islands of Borneo and Sumatra, but many fossils have been found in Pleistocene (Pleistocene) strata in southern China and other areas. Orangutans are considered to have branched off from the trunk of humans and African apes earlier in the Anthropoidea. Males are about 1.4 meters tall and weigh about 70 kilograms, but there are known to be cases of males weighing over 100 kilograms. There is a large difference between the sexes, with females only reaching around 40 kilograms. Their upper limbs are significantly longer than their lower limbs. Their entire body is reddish brown and covered with sparse long hair, and their face is dark and hairless. Old males have a larger face due to the folds of skin that extend from the cheeks to the sides. A huge laryngeal pouch is developed from the throat to the fore chest. They have 32 teeth, the same as humans, but males have strong canines with a noticeable gap between them. The volume of the skull is 400cc, which is significantly larger than the 100cc of the gibbon, a small ape. It takes about 10 years to reach sexual maturity, and they give birth to one child per litter. They live in the trees of the rainforest and rarely descend to the ground. They walk on the ground very clumsily, placing the outer edge of the sole of the foot and the back of the middle part of the hand on the ground. They are good at brachiation using their powerful forelimbs, but because of their heavy weight, they are cautious and their movements appear slow. They build a new bed in the treetops every evening to sleep. Its diet is heavily biased towards fruit, with a particular preference for durian fruit, but it will also eat tree leaves and bird eggs.

They are the only anthropoid monkeys that live solitary lives without forming unitary groups, and there is particularly strong tension between males, who avoid contact by keeping a large distance from each other. They live in a very free-spirited society, mating with females that move freely between them and then separating from them. There is a theory that this society is a form in which the bond between male and female gibbon-type pairs has been severed. As the children grow up, they also leave their mothers and live solitary lives. While chimpanzees have analytical intelligence, this species' intelligence is said to be insightful. Their population has declined sharply due to overhunting and deforestation, and there are calls for their protection.

[Junichiro Itani]

"In pursuit of the Orangutan: The Lonely Forester" by J. MacKinnon, translated by Hideo Ohara and Sayaka Ono (1977, Hayakawa Publishing)

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

哺乳(ほにゅう)綱霊長目ショウジョウ科の動物。オランウータンの名は「森の人」を意味するマレー語に由来し、別名をショウジョウ（猩猩）ともいう。テナガザル類とともにアジアの類人猿Asian apesを、またアフリカの3種の類人猿とともに大形類人猿great apesを構成する。現生種はボルネオ島とスマトラ島に分布するが、中国南部などの更新世（洪積世）の地層から多くの化石が発見されている。オランウータンは、ヒトニザル上科のなかで、ヒトとアフリカの類人猿の幹から、より早い時期に分岐したと考えられている。雄の身長は約1.4メートル、体重は約70キログラムであるが100キログラムを超す例も知られている。性差が大きく、雌は40キログラム前後にしか達しない。上肢は下肢に比べて著しく長い。全身赤褐色で、まばらな長毛に覆われ、顔面は無毛で暗色。老雄は頬(ほお)から側方に広がる皮膚のひだのため顔幅が大きくみえる。巨大な喉頭嚢(こうとうのう)がのどから前胸にかけて発達している。歯の数は32本でヒトと同じであるが、雄の犬歯は強大で歯隙(しげき)が目だつ。頭蓋(とうがい)内容量は400ccと、小形類人猿のテナガザルの100ccに比し格段の開きがある。性的成熟には約10年を要し、1産1子。多雨林の樹上生活者で、めったに地上に降りることはない。地上歩行は、足の裏の外縁と手の中節背面を地面につけ、きわめて不器用である。強力な前肢を用いての腕渡り（ブラキエーション）を得意とするが、重い体重のために慎重で、動作は緩慢にみえる。毎夕、樹上に新しいベッドをつくって眠る。食性は果実食への偏りをみせ、とくにドリアンの実を好むが、木の葉、鳥の卵なども食べる。

　真猿類中唯一の、単位集団をもたない単独生活者で、とくに雄の間には強い緊張関係があって、互いに大きな距離を保って接触を避けあっており、その間を自由に行動する雌と配偶者関係を結んではまた離れるという、いたって気ままな社会をもっている。この社会を、テナガザル型のペアの雌雄を結ぶボンド（結び付き）が切れた形態であるとする説がある。子供も成長につれて母親から離れ、単独生活に入る。チンパンジーの知能が分析的であるのに対し、本種のそれは洞察的だといわれる。乱獲と森林の伐採により個体数が激減し、保護の必要が叫ばれている。

［伊谷純一郎］

『J・マッキノン著、小原秀雄・小野さやか訳『オランウータンを追って――孤独な森の住人』（1977・早川書房）』

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