A Sumatran orangutan in Indonesia treated itself using a mixture made from herbs to heal a large gash on its cheek, scientists say.
This is the first time that it has been recorded that an animal treated an injury with the help of medicinal plants.
After the researchers saw Rakus apply herbal poultices to his face, the wound closed and healed within a month.
Scientists say this behavior may have originated from a common ancestor shared by humans and great apes.
"They are our closest relatives and this again points to the similarities we share with them.
"We are more alike than we are different," said biologist Izabela Laumer, from the Max Planck Institute in Germany, and co-author of the study.
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A research team from Gunung Leuser National Park, Indonesia, spotted Rukus with a large gash on his cheek in June 2022.
They believe he was injured in a fight with rival male orangutans, because he produced loud cries called "long calls" in the days before the wound was noticed.
The team then saw Rakus chewing the stem and leaves of a plant called Akar Kuning - an anti-inflammatory and anti-bacterial plant that is also used locally to treat malaria and diabetes.
He applied the liquid to his cheek for seven minutes.
Rakus then spread the chewed leaves over the wound until it was completely covered.
He continued to eat the plant for over 30 minutes.
The mixture and leaves then seem to have worked - the researchers saw no signs of infection and the wound closed within five days.
After a month, Rakus was completely cured.
The scientists concluded that Rakus knew he was applying the drug to himself because orangutans very rarely eat this particular plant, as well as because of the length of the treatment.
"He reapplied the mixture, and later he also put in more solid plant matter.
"The whole process took a really long time - that's why we think he was deliberately applying it," explains Dr. Laumer.
The researchers also saw that Rakus was resting much longer than usual - more than half a day - suggesting that he was trying to recover from his injury.
Scientists were already aware that apes used drugs to try to heal themselves.
In the 1960s, biologist Jane Goodall saw whole leaves in chimpanzee feces, while others documented seeing great apes ingesting leaves with medicinal properties.
But they had never seen a wild animal apply herbs to a wound.
Dr. Laumer says it's possible this is the first time Rakus has done this type of treatment.
"It is possible that he accidentally touched the wound with his finger that had the plant on it."
"And then, because the plant contains quite strong pain-relieving substances, he may have felt immediate pain relief, which is why he kept applying it again and again," she says.
Or he may have learned this method by observing other orangutans in his group.
The researchers will now closely monitor other orangutans to see if they can observe the same medical skills demonstrated by Rakus.
"I think in the next few years we're going to discover more types of behavior and more abilities that are very human-like," she suggests.
The research was published in the scientific journal Sajentifik reports.
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