Species & Subspecies

There are two orangutan species, the Bornean (Pongo pygmaeus) and Sumatran (Pongo abelii) orangutans.

The Bornean and Sumatran lineages diverged from one another about 1.1 to 2.3 million years ago.

Genetic studies have identified three Bornean orangutan subspecies: The northwest (P.p.pygmaeus), central (P.p.wurmbii), and northeast (P.p.morio). Each subspecies is differentiated by its geographic distribution and overall body size.

• Central Bornean orangutans (P.p.wurmbii) inhabit southern West Kalimantan and Central Kalimantan regions of Borneo. They are the largest of the three Bornean subspecies.
• Northeast Bornean orangutans (P.p.morio) inhabit Sabah and East Kalimantan regions of Borneo. They are the smallest of the three Bornean subspecies.
• Northwest Bornean orangutans (P.p.pygmaeus) inhabit northern West Kalimantan and Sarawak regions of Borneo. They have a mid-size body, intermediate between the other two subspecies.
• Preliminary genetic research indicates Northeast Bornean orangutans inhabiting the Sabah and East Kalimantan regions of Borneo may be two distinct subspecies. Therefore orangutan taxonomy may diversify in the future as more genetic and phylogenetic information becomes available.

Currently there are no subspecies of Sumatran orangutans recognized.

Nomenclature

Orangutan is a Malay name and when translated means person of the forest.

Fossil Record

Primates are classified into two suborders, Prosimii (prosimians) and Anthropoidea (non-prosimian primates). Anthropoids are further divided into New World and Old World anthropoids. New World anthropoids are native to North and South America whereas Old World anthropoids are native to Africa and Asia. Prosimians are characterized as primitive due to some of their physical characteristics that are not shared in other primates. For example prosimians have a nose structure that remains moist, called a rhinarium (also found in dogs), which enhances their sense of smell. Apes are divided into greater and lesser ape categories. Lesser apes include 11 recognized species of gibbons native to Southeast Asia. Greater apes include orangutans, chimpanzees, bonobos, and gorillas native to Africa and Asia.

Apes diverged from old world monkeys about 25 million years ago. There are many differences between apes and monkeys including the following characteristics.

• Apes have no tail
• Apes usually have a larger body size and weight
• Apes have a more of an upright body posture
• Apes have broader chests
• Apes rely more on vision than on smell (have a short broad nose rather than a long snout)
• Apes have a larger brain in relation to their body size. They are capable of more advanced thought (some have been taught sign language), tool use, and have problem solving capabilities.
• Apes have longer gestations and require longer time periods to mature.
• Apes tend to be less arboreal (tree-dwelling) and more terrestrial (ground-dwelling). This has led to changes in the muscle and skeletal structure of their arms because they are not as adapted for tree-dwelling (brachiation-swinging from trees) as monkeys are.

The first primates without tails originated in East Africa about 17 to 23 million years ago during the Miocene epoch. These fossil ancestors to modern apes were called Proconsul. Similar to orangutans, Proconsul walked on the ground by supporting their weight on the outside edges of their palms.

The fossil record indicates that lesser and greater apes diverged from one another about 18 million years ago. The Pongidae family (orangutans) diverged about 14 million years ago, gorillas about 7 million years ago, and chimpanzees and humans diverged about 6 million years ago.

Orangutan ancestors that looked most similar to present-day orangutans appeared in the fossil record about two million years ago during the Pleistocene epoch. The teeth of these ancient orangutans have been found in the Yunnan and Guangxi provinces of Southern China and in Laos, Vietnam, Sumatra, Java, Kalimantan, and Sarawak.

Humans have about 98.4% of our DNA (deoxyribonucleic acid-genetic material) in common with chimpanzees, 98.3% with gorillas, and 98% with orangutans. This genetic information has provided insight on human relatedness to great apes.

There are several similarities between humans and orangutans, including the following.

• Presence of a particular vein in the arm
• Certain structures of the teeth and bones
• A long gestation (period of pregnancy)
• Absence of genital swelling during periods of sexual receptivity
• Absence of knuckle walking. When chimpanzees and gorillas walk on the ground they ball their hands and support their weight on their knuckles—hence the term, knuckle walking. Similar to how human children crawl (placing the palms of their hands on the floor), orangutans walk on the ground supporting their weight on the outside edges of their palms.