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Chimpanzees use medicinal leaves to perform first aid, scientists discover

Scientists studying chimpanzees in Budongo Forest, Uganda, have observed that these primates don't just treat their own injuries, but care for others, too—information which could shed light on how our ancestors first began treating wounds and using medicines.

Although chimpanzees elsewhere have been observed helping other community members with medical problems, the persistent presence of this behavior in Budongo could suggest that medical care among chimpanzees is much more widespread than we realized, and not confined to care for close relatives.

"Our research helps illuminate the evolutionary roots of human medicine and health care systems," said Dr. Elodie Freymann of the University of Oxford, first author of the article in Frontiers in Ecology and Evolution. "By documenting how chimpanzees identify and utilize medicinal plants and provide care to others, we gain insight into the cognitive and social foundations of human health care behaviors."

Community care

The scientists studied two communities of chimpanzees in the Budongo Forest—Sonso and Waibira. Like all chimpanzees, members of these communities are vulnerable to injuries, whether caused by fights, accidents, or snares set by humans. About 40% of all individuals in Sonso have been seen with snare injuries.

The researchers spent four months observing each community, as well as drawing on video evidence from the Great Ape Dictionary database, logbooks containing decades of observational data, and a survey of other scientists who had witnessed chimpanzees treating illness or injury.

Any plants chimpanzees were seen using for external care were identified; several turned out to have chemical properties which could improve wound healing and relevant traditional medicine uses.

During their direct observational periods, the scientists recorded 12 injuries in Sonso, all of which were likely caused by within-group conflicts. In Waibira, five chimpanzees were injured—one female by a snare, and four males in fights. The researchers also identified more cases of care in Sonso than in Waibira.

"This likely stems from several factors, including possible differences in social hierarchy stability or greater observation opportunities in the more thoroughly habituated Sonso community," said Freymann.

The roots of modern medicine?

The researchers documented 41 cases of care overall: seven cases of care for others—prosocial care—and 34 cases of self-care. These cases often included several different care behaviors, which might be treating different aspects of a wound, or might reflect a chimpanzee's personal preferences.

"Chimpanzee wound care encompasses several techniques: direct wound licking, which removes debris and potentially applies antimicrobial compounds in saliva; finger licking followed by wound pressing; leaf-dabbing; and chewing plant materials and applying them directly to wounds," said Freymann.

"All chimpanzees mentioned in our tables showed recovery from wounds, though, of course, we don't know what the outcome would have been had they not done anything about their injuries.

"We also documented hygiene behaviors, including the cleaning of genitals with leaves after mating and wiping the anus with leaves after defecation—practices that may help prevent infections."

Who cares?

Of the seven instances of prosocial care, the researchers found four cases of wound treatment, two cases of snare removal assistance, and one case where a chimpanzee helped another with hygiene. Care wasn't preferentially given by, or provided to, one sex or age group. On four occasions, care was given to genetically unrelated individuals.

"These behaviors add to the evidence from other sites that chimpanzees appear to recognize need or suffering in others and take deliberate action to alleviate it, even when there's no direct genetic advantage," said Freymann.

The scientists call for more research into the social and ecological contexts in which care takes place, and which individuals give and receive care. One possibility is that the high risk of injury and death which Budongo chimpanzees all face from snares could increase the likelihood that these chimpanzees care for each other's wounds, but we need more data to explore this.

"Our study has a few methodological limitations," cautioned Freymann.

"The difference in habituation between the Sonso and Waibira communities creates an observation bias, particularly for rare behaviors like prosocial health care. While we documented plants used in health care contexts, further pharmacological analyses are needed to confirm their specific medicinal properties and efficacy.

"Also, the relative rarity of prosocial health care makes it challenging to identify patterns regarding when and why such care is provided or withheld. These limitations highlight directions for future research in this emerging field."