An orangutan named Rakus went through a difficult time in the summer of 2022.
Researchers heard a fight between male orangutans in the treetops of a rainforest in Sumatra, Indonesia; A day later, they saw that Rakus had a pink scar under his right eyelid.
A piece of meat the size and shape of a puzzle piece was missing. When Rakus, who was probably in his 30s, made a long speech, researchers noticed another wound inside his mouth.
For the next few days, researchers followed Rakus from a distance and saw something so surprising that they eventually reported it in great detail in the journal Scientific Reports.
Rakus was observed repeatedly chewing the leaves of a particular vine plant over several days, according to research published Thursday. Climbing vine is not a typical food for orangutans, but it is known to humans as a pain reliever.
At least once, Rakus made a paste from the chewed leaves and applied it to his face. For the first time, an animal was seen applying medicine to a wound on the skin.
“This is the first documentation of external self-medication by applying the leaves as a poultice, as humans do to treat wounds and pain,” said Michael Huffman, an associate professor at Kyoto University’s Wildlife Research Center. Japan, which was not included in the new study.
Rakus’ wound never showed signs of infection and healed within a week.
The discovery is new evidence that orangutans can identify and use pain-relieving plants. A growing body of research suggests that other animal species can also self-medicate, with varying levels of sophistication.
The researchers behind the study think that great apes’ ability to identify drugs and treat wounds may date back to a common ancestor with humans.
New evidence that orangutans self-medicate
The discovery was possible because Rakus spent his days in a protected area of rainforest called the Suaq Balimbing research area in Indonesia’s Gunung Leuser National Park.
Researchers have been observing orangutans there since 1994. Today, approximately 150 orangutans call the area home. Rakus, first observed here in 2009, is either a resident or a frequent visitor.
Scientists typically track an orangutan in the area from the early morning hours (when it leaves its night burrow) until it builds a new night burrow about 12 hours later.
“We’re not disturbing the orangutan,” said new study author Isabelle Laumer, a primatologist and cognitive biologist at the Max Planck Institute for Animal Behavior in Germany. “They are completely tolerant of us following them.”
Laumer said researchers had not previously observed orangutans in the region self-medicating the way Rakus did, and it was not clear how they developed this behavior.
Laumer said Rakus may have learned to treat his wound “through individual innovation” when he accidentally touched his finger to the wound with pain-relieving leaf juice. Or it may have learned the behavior culturally from other orangutans early in life.
Orangutans learn socially and have been shown to be skilled with tools. They develop complex knowledge about foods from their mothers.
“For example, they learn a lot about what types of fruits to eat, where to find them, when to find them, when to ripen, how to process them,” Laumer said. “Some orangutans feed on up to 400 different plants. … That’s actually a pretty intense knowledge to acquire.”
Did humans learn medical plans from animals?
Evidence of animal self-medication has increased in recent years.
In the 1960s, renowned primatologist Jane Goodall noticed that chimpanzees in Tanzania were eating whole leaves of a plant later identified as the Aspilia shrub species. Decades later, Huffman wrote a paper describing how a different population of chimpanzees ate the bitter sap of a particular daisy, but only occasionally, and other behaviors suggested they were sick.
Researchers think chimpanzees developed this type of behavior to treat or prevent parasites.
A flood of research in the 1990s and 2000s identified additional examples of self-medication.
A notable study of Bornean orangutans in 2008 documented three females rubbing their bodies with a paste of the chewed Dracaena cantleyi plant that local natives use to relieve joint and bone pain.
Huffman said he thinks all animal species self-medicate to some degree. Researchers have even documented the practice in insects.
“This shows us that animals have control over their lives,” he said. “Their ability to act flexibly to adapt to certain conditions that require their survival.”
He theorized that ancient humans gained the ability to identify medicinal plants and substances by closely observing animals.
“Many of the medicines that humans have used throughout our history as a species have arisen as a result of our close connection with nature and the ability to look to other animals for advice and make inferences based on what we have learned,” Huffman said. “I don’t know of any plants documented for use by animals as medicine that are not used by humans. And I think it’s humans who learn from animals.”
Laumer said his team’s findings on a species that is 97% genetically similar to humans could provide insight into how ancient primates developed their drug use tendencies.
“It is possible that our last common ancestor already showed similar forms of ointment behavior,” he said.
Laumer added that the new findings also show how much can be learned from orangutans, which are considered critically endangered. The rainforests where Sumatran orangutans live are disappearing as land is converted to agriculture and climate change exacerbates forest fires.
Latest estimates from 2016 put the number at fewer than 14,000.
This article first appeared on NBCNews.com.