Taxonomy
There is evidence that there was gene flow between the geographically isolated Bornean Orangutan populations until recently. The Bornean and Sumatran Orangutan species diverged 1.5 – 1.7 million years ago. This occurred well before the two islands (Borneo and Sumatra) separated. The two species of orangutan are more distantly related than the Common Chimpanzee and the Bonobo. Despite this difference, the two orangutan species were only considered subspecies until as recently as 1996, following sequencing of mtDNA.
The Bornean Orangutan has three subspecies:
- Northwest Bornean Orangutan P. p. pygmaeus - Sarawak (Malaysia) & northern West Kalimantan (Indonesia)
- Central Bornean Orangutan P. p. wurmbii - Southern West Kalimantan & Central Kalimantan (Indonesia)
- Northeast Bornean Orangutan P. p. morio - East Kalimantan (Indonesia) & Sabah (Malaysia)
The population currently listed as P. p. wurmbii may be closer to the Sumatran Orangutan (P. abelii) than the Bornean Orangutan. If confirmed, abelii would be a subspecies of P. wurmbii (Tiedeman, 1808). Regardless, the type locality of pygmaeus has not been established beyond doubts, and may be from the population currently listed as wurmbii (in which case wurmbii would be a junior synonym of pygmaeus, while one of the names currently considered a junior synonym of pygmaeus would take precedence for the taxon in Sarawak and northern West Kalimantan). To further confuse, the name morio, as well as various junior synonyms that have been suggested, have been considered likely to all be junior synonyms of the population listed as pygmaeus in the above, thus leaving the taxon found in East Kalimantan and Sabah unnamed.
