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A Sumatran orangutan has been seen treating a facial wound with a plant with known medicinal properties for the first time.
In a new paper published in Nature, scientists document their observation of the “possibly innovative behavior.” Three days after they first spotted the orangutan, called Rakus, with a large wound under one eye, they saw him selectively tear leaves off a liana climbing vine. He then chewed the leaves to produce a juice which he repeatedly applied to his wound. Finally, he used the chewed up leaves to cover the wound.
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It is not the first recorded instance of apes self-medicating. But it is the first time one has been seen using a plant whose healing properties are already known. Previous analysis of liana plants show they have antibacterial, anti-inflammatory, analgesic, and antioxidant properties.
Rakus’s wound had closed up five days later, and healed completely within a few weeks.
Intentional behavior
In the study, the scientists say that the systematic way in which Rakus applied the plant juice and chewed leaves indicate the action was intentional.
However, they are unsure whether he came up with the method on his own or learned it from other orangutans. One possibility it that other orangutans have learned that liana plants have pain-numbing effects after initially accidentally touching wounds while feeding on the leaves. Orangutans learn social behavior from when they are young into adulthood by observing each other. They may have passed the method on to each other this way.
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But the scientists had never observed this specific behavior in that population of orangutans. They speculate that this might be because they have rarely seen wounded orangutans there due to good environmental conditions and social tolerance between individuals. Rakus, however, appears to have been wounded as he had fought with other males in the area to assert dominance.
It’s possible that Rakus learned to use liana leaves for wound treatment when he was young. Male orangutans travel far form their birth area as they grow up, making it hard to know where they first came from.
Self-medicating apes
When other great apes have been documented self-medicating, it hasn’t always been known if the treatments they choose really work.
In one case, scientists recorded chimpanzees applying insects to their wounds. But they never learned whether those insects had medicinal properties or not.
The ingestion of plants as medication is more widespread. It has been observed in chimpanzees, bonobos, gorillas, and white-handed gibbons. One study reported orangutans eating plant species to help with parasite infections.
