A specialized rainforest mammal

Some of the world’s oldest rainforest areas are located in Borneo, the third largest island in the world. The lush rainforest is home to a myriad of endemic species, which existence depends on in this unique ecosystem, including the great Bornean orangutan. This unique forest environment has shaped the life of the orangutan and made its body perfectly adapted to a life in the treetops. 


An arboreal body

The orangutans long arms and hook like fingers and toes is excellent suited for grasping branches and thus movement above ground in the forest canopy. The orangutans even have a unique method of arboreal locomotion called “quadrumanous scrambling” (having all four feet adapted to function as hands). As their hip and shoulders are highly mobile the orangutans can easily put their legs behind their heads like human acrobats. When they move along the ground, orangutans typically walk quadrupedally (walking on all four limbs) but they have also been observed moving bipedally (walking upright on two feet).

The red color

The orangutans reddish coat is well suited and adapted to its rainforest environment: As sunlight filters through the rainforest canopy, the numerous levels of vegetation primarily absorbs red light in the color spectrum. When most of the red light is filtered out, it is difficult to detect any red looking features in the forest environment, thereby enabling the orangutan to visually disappear in the rainforest environment. The orangutan eyes are also well adapted to a life in the tropics, as the dark brown eye color protects the eye from sunlight (absorbing sunlight before damaging UV light can penetrate to the back of the eyes). 

Specialized eating methods

Like humans, the orangutans have opposable thumbs and toes, which makes them capable of using various tools for foraging or nest-building.  For foraging, their 32 permanent teeth (same as humans) makes them capable of opening hard shelled or thorny fruit by gripping it firmly between their teeth until a weak spot is breached. This feeding method gives orangutans a great advantage, as other species in the forest have to wait until the fruits become fully ripe.

Longest non-human reproduction rate in the world

The orangutans has the longest childhood of all great apes, and is also believed to have the longest childhood of any mammal in the world (around 15 years), as females do not usually become mothers before they have reached their teens (up to 18 years of age), and is ready for 8.5 months of pregnancy. As mothers they also have the longest interbirth interval in the world (around 7 years), contributing to the highest survival rate of offsprings among all the great apes.

Advantage of no large predators

The arboreal life has also made orangutans less vulnerable to predation, thereby reducing their mortality rate. The reduced adult mortality is thought to have allowed the long investment required to grow large brains: As apes with rather small brains began to invent tools, the apes became increasingly dependent on culture, creating a recurrent positive feedback loop, where selection favored even larger brains, which improved culture, and so on. Great apes therefore probably started out smart because they were safe from predators, and ended up being even smarter because their large brains and slow life histories allowed culture to develop and flourish.

Adaption to local environments

The two main species of orangutans (Sumatran and Bornean) have different reproductive and social behaviours, probably illustrating the difference of habitat. As an example, the Sumatran orangutan is found in higher densities and at higher elevations (up to 1,500 meters), which has been attributed to a more productive Sumatran rainforest growing on very fertile soils. Bornean orangutan females also share less social time together than Sumatran females, and bornean orangutans have a more flexible diet than Sumatran orangutans (probably evolved due to longer periods of low fruit abundance on Borneo). 

Read more about the life of the orangutans here >>