Chimpanzees perform leaf cures and clean themselves after sex and after defecating.

Deep in the Burongo Forest, Uganda, live two communities of chimpanzees: Sonso and Waibira. Like any other group of apes, their members are susceptible to injury, whether accidentally, through fights among themselves, or through traps set by humans. But afterward, as a team of scientists from Oxford University has observed, the primates pluck medicinal leaves and attempt to use them to treat not only their own wounds but also those of others. The discovery sheds light on how our ancestors began using medicines and performing "first aid." Not only that. The study also shows that the apes clean themselves with leaves after sex and defecation.

"We knew that chimpanzees rub leaves on their wounds, but I think this is the first study in which we've shown chimpanzees chewing botanical material and applying it directly to a wound," Elodie Freymann of Oxford University, first author of the paper published in Frontiers in Ecology and Evolution, told this newspaper.

According to the researchers, while chimpanzees have been observed elsewhere helping other members of the community with medical problems, the persistent presence of this behavior at Budongo could suggest that medical care among these apes is much more widespread than previously thought and is not limited to caring for close relatives. "Our research helps shed light on the evolutionary roots of human medicine and healthcare systems," Freymann says.

The researchers followed the chimpanzees for four months and identified all the plants they used for external care; several turned out to have chemical properties that could improve wound healing and have other relevant uses in traditional medicine.

During their direct observation periods, scientists recorded twelve injuries at Sonso, likely caused by intragroup conflicts. At Waibira, five chimpanzees were injured: one female by a trap and four males in fights.

The researchers identified more cases of attention in Sonso than in Waibira. "This is likely due to several factors, including possible differences in the stability of the social hierarchy or greater opportunities for observation in the more habituated Sonso community," says Freymann.

The researchers documented 41 instances of caregiving in total: seven involving caregiving to others (prosocial care) and 34 involving self-care. These instances often included diverse caregiving behaviors, which could be addressing different aspects of an injury or reflecting a chimpanzee's personal preferences.

Chimpanzee wound care encompasses several techniques: direct licking of the wound, which removes debris and potentially applies the antimicrobial compounds in saliva; finger licking followed by pressure on the wound; leaf rubbing; and chewing plants and applying them directly to the wounds. All the chimpanzees recovered from their wounds, "although, of course, we don't know what the outcome would have been if they had done nothing to remedy their injuries," Freymann notes.

"We also documented hygiene habits, such as cleaning the genitals with leaves after mating and the anus after defecating, practices that can help prevent infections," he says.

Of the seven instances of prosocial care, the researchers found four cases of wound treatment, two cases of assistance with trap removal, and one case in which one chimpanzee assisted another with hygiene. The care was not provided preferentially to one sex or age group. On four occasions, care was provided to individuals who were not genetically related.

"These behaviors add to evidence from other sites that chimpanzees appear to recognize need or suffering in others and take deliberate steps to alleviate it, even when there is no direct genetic advantage," Freymann notes. "Chimpanzees are highly social animals and live in close-knit groups. Although their members are not closely related, they form very close bonds with each other. To me, these instances of prosocial care represent potential demonstrations of compassion and empathy: chimpanzees care for others because they recognize that they need care," she emphasizes.

The authors acknowledge that further studies are needed to clarify the causes of this grooming, but one possibility is that the high risk of injury and death faced by all Budongo chimpanzees due to snares could increase the likelihood of them caring for each other's wounds. But who is the one doing the grooming and who is the caregiver?

"Unfortunately, with the data we have, there is still no profile," the researcher admits, "but that's also interesting. It doesn't seem to be determined by sex, age, or rank. It seems that anyone can be the caregiver, anyone can be the healer, and anyone can be the healed."

It's not just chimpanzees who heal with medicinal plants. A year ago, the case of a Sumatran orangutan was documented applying a type of allamanda, a climbing plant used in traditional medicine to treat wounds and conditions such as dysentery, diabetes, and malaria, to a fresh wound on his face.

For Freumann, these findings "demonstrate that the foundations of our human health systems date back to older times than we thought. Compassion and empathy for others, as well as the ability to transfer knowledge from self-care to caring for others, may have been present in the last common ancestor of Pan-Homo."