It is the first time a creature in the wild has been recorded treating an injury with a medicinal plant.
After researchers saw Rakus applying the plant poultice to his face, the wound closed up and healed in a month.
Scientists say the behaviour could come from a common ancestor shared by humans and great apes.
“They are our closest relatives and this again points towards the similarities we share with them. We are more similar than we are different,” said biologist Dr Isabella Laumer at the Max Planck institute in Germany and lead author of the research.
Human supremacists will define intelligence as being like a human and not like an animal, and then test animal intelligence on that measure.