Chimpanzees have recently been observed to apply insects on their wounds and that of their conspecifics (i.e. individuals of the same community and species) for healing. The new study, conducted by researchers from Osnabruck University and the Ozouga Chimpanzee Project in the Loango National Park, Gabon, and published in Current Biology, reports findings from investigating 76 wounds in 22 different chimpanzees. The Rekambo community consists of ≈ 45 chimpanzees and was observed for their social behaviour, hunting behaviour, tool use and communication skills.
“Our two closest living relatives, chimpanzees and bonobos, for instance, swallow leaves of plants with anthelmintic properties and chew bitter leaves that have chemical properties to kill intestinal parasites,” Simone Pika, one of the authors of the study and co-director of the Ozouga Chimpanzee project, said in a press communication with indianexpress.com
This behaviour was first filmed – almost by chance – by a volunteer, Alessandra Mascaro, at the Ozouga Chimpanzee Project, who saw a mother chimpanzee catch something from underneath a bush, put it between her lips and apply it to the wound of her adolescent son. The team then decided to focus future research efforts specifically on wounded individuals.
In another incident, an adult male was seen wounded and another adult female chimpanzee was suddenly observed catching an insect, which she handed over to the wounded male who applied it onto his wound. Over the next 15 months, the team recorded 22 such instances between Nov 2019 and Feb 2021.
Self-medication has been observed across a wide spectrum of species, Mascaro et al. (2022) highlight. Wood ants, for instance, have been known to use antimicrobial resin from conifer trees in their nests. Parasite infected monarch butterflies, in a bid to protect their offspring, lay their eggs on antiparasitic milkweed. Primates have been known to chew on Vernonia amygdalina that has antiparasitic properties, but no nutrition as such.
So far, among the Great Apes, eating plant parts or non-nutritional substances has been observed. But this is the first study that reports such a behaviour, involving a skin-level (topical) application of animal matter to wounds on the skin. The insect species that the chimpanzees preferred has not been identified so far, but the study does make some observations. One, they are flying insects, as chimpanzees moved their hands quite fast in order to catch them. Two, sometimes, these insects are caught under a leaf or a branch, and are dark in colour. Three, never did the researchers observed the eating of insects.
This might have two implications. One, that insects might actually have some medical functions, for instance anti-inflammatory properties. After all, all chimpanzees practising this behaviour were wounded without exception. Indeed, some insect species do have antibiotic and antiviral properties but it still remains to be seen whether it is not merely a local practice in that particular chimpanzee community (just like some cultural treatments in human societies that have no direct medical function). At any rate, the study notes, it gives an interesting peek into the origins of human traditional medicine.
The other also important implication, according to Mascaro et al. (2022), is that it points towards the cognitive and behavioural sophistication of the species. The study highlights that this shows that ‘individuals not only treat their own wounds but also that of their other non-related members of the species.’ This clear prosocial behaviour is rarely observed in non-human societies.
The observation of prosocial behaviour – actions intended to help others, and arising out of empathic concerns in humans – raises important questions for the study of evolution. Evolution, at least in theory, claims that any individual acts in self-interest. Chimpanzees, being our closest relatives, offer a very good template to study this template in non-human primates and, ultimately, reconstruct the development of this behaviour in humans.
Other studies, such as Mitani (2009) have documented the cooperation, territorial patrolling, meat sharing as well as aggression. However, other studies, such as Silk et al. (2005) report a complete non-existence of cooperation and nothing short of an ‘indifference’ towards unrelated conspecifics. The findings of this study show, if anything, that the debate is far from settled; and that, chimpanzees will continue to surprise us with unexpected new behaviours.
The author is a research fellow at the Indian Institute of Science (IISc), Bengaluru, and a freelance science communicator. He tweets at @critvik