Why are orang-utans orange? It doesn’t seem to be a camouflage mechanism. And why are they so hairy? They live in tropical forests after all.
• Orang-utans’ colouring does help them blend in. The water in peat-swamp forests, where orang-utans live, tends to be a muddy orange. Sunlight reflected off this water can give the forest an orange cast, making orang-utans surprisingly hard to see in dappled light. Many orang-utan nests, up in the forest canopy, contain orangey-brown dead leaves, and some trees have reddish leaves, especially when young.
Ground-based predators would view orang-utans in the canopy as a mere silhouette. In such circumstances orange may stand out less than black, which may be more suited to blending in with the forest floor. Dark African apes such as gorillas spend much more time on the ground than orang-utans, while some other canopy-dwelling primates have a similar ruddy colour to orang-utans. Among these are , which live in the same Borneo forests as orang-utans.
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As for orang-utans being hairy, there are numerous possible reasons for this. Orang-utans are exposed to direct sunlight up in the canopy, so hair could serve to protect their skin from the sun. It may also provide insulation and temperature control, trapping a layer of relatively cool air close to the skin by day and keeping the skin dry and warm at night and in cool rainy weather. Hair also protects against insect bites and helps break the outline of the animals’ silhouette in the canopy when viewed from below.
Finally, dominant “flanged” male orang-utans have long hair on their arms and at the base of their back. This makes them look larger, helping them dominate other males and attract females.
Mark Harrison Orang-utan Tropical Peatland Project and David Chivers Reader in Primate Biology, The Anatomy School, University of Cambridge, UK
• Orang-utans may not need camouflage, given their size and strength. And if their hair is not for camouflage, the fact that reddish hair is common in primates such as proboscis and red leaf monkeys, and in other mammals such as tree shrews, squirrels, foxes, deer and flying foxes, suggests that it isn’t an awkward thing to have.
As to whether being orange provides camouflage, that depends on the environment. Some marine species that live at depth are well camouflaged despite being bright red, because red doesn’t stand out in the low light under water. Something similar applies to orang-utans.
The explanation lies in the way sunlight penetrates the forest canopy, bouncing off vegetation as it does so. Leaves absorb red, orange and violet light for photosynthesis, reflecting green. So by the time sunlight has reached the forest floor, it has been robbed of reds and oranges. In this sort of light, orang-utans look like dull brown lumps. They can be so well camouflaged that several times I have walked past having failed to see them sitting on the ground half a metre away. I have twice come within a hair’s breadth of tripping over them.
“In shade, orang-utans are so well camouflaged that I have failed to see them sitting half a metre away”
The explanation above is something I heard from Jared Diamond, who has studied birds of paradise in Papua New Guinea. He described males displaying in columns of dappled sunlight: as they moved in and out of the light, they changed from dull brown to spun gold, as though disco dancing under strobe lights.
Anne Russon York University, Toronto, Canada
The writer is the editor of The Evolution of Thought: Evolution of great ape intelligence (Cambridge University Press, 2007) and the author of Orangutans: Wizards of the rainforest (Firefly, 2004) – Ed
Several replies noted the similarity between the words “orang” and “orange” – but only one explained their derivation in detail – Ed
• Orang-utans may be orange, but the name has nothing to do with their colour. It comes from Malay and means “person of the forest”, orang being Malay for “person”. The word “orange” – originally meaning the fruit, but later used for the colour too – came into English via a trail of other languages.
It ultimately comes from India (Tamil via Sanskrit), from where it arrived into English in the 15th century via Persian, Arabic, Italian and French. So “orang-utan” and “orange” are unconnected etymologically.
Linguistic coincidences are quite common, as it happens. The word for “dog” in , an indigenous Australian language, is dog, although the word is not borrowed from English. Similarly, the word for “honey” in both Hawaiian and ancient Greek is meli. Chance similarities are a major problem in establishing whether two languages derive from a common ancestor.
Sometimes these coincidences take on a life of their own. At one time a berfry was a tower, but when people started to associate the first part of it with the word “bell”, it changed to “belfry” and started to mean a tower with a bell in it. So far, no one is claiming that orang-utans are so named because they are orange, but it’s not inconceivable that one day someone might.
David Willis, Department of Linguistics University of Cambridge, UK