Why Would a Chimpanzee Use a Tool to Clean a Corpse's Teeth?

Last week a few people wrote to me about a very interesting essay by Dr. Edwin J. C. van Leeuwen and his colleagues in Scientific Reports titled "Tool use for corpse cleaning in chimpanzees." It really piqued my interest. The abstract for the report reads as follows:

For the first time, chimpanzees have been observed using tools to clean the corpse of a deceased group member. A female chimpanzee sat down at the dead body of a young male, selected a firm stem of grass, and started to intently remove debris from his teeth. This report contributes novel behaviour to the chimpanzee’s ethogram, and highlights how crucial information for reconstructing the evolutionary origins of human mortuary practices may be missed by refraining from developing adequate observation techniques to capture non-human animals’ death responses.

The entire essay is available online and I encourage you to read it and to look at the wonderful photographs of Noel, a wild-born 33-year-old female chimpanzee living at the Chimfunshi Wildlife Orphanage Trust in Zambia. She "attended the dead body of Thomas, a nine-year-old male whom she adopted (sensu⁶) when his mother died four years earlier." (Please see Note 1 for the reference referred to as sensu^6.) We're also told, "The majority of the group visited Thomas’ body at least once⁷, but when most chimpanzees were lured away with highly attractive food, Noel remained at his body and cleaned his teeth with a grass tool. Nina, her adolescent daughter, stayed at her side and observed the cleaning efforts of her mother."

The authors stress that this is the first observation of tool-use in the death response of a nonhuman animal. It's an incredibly stimulating exercise to ponder why Noel did what she did and to assess the various explanations offered by the authors of this fascinating report. To whet your appetite, they offer a number of possible explanations that include:

Noel's behavior may have "emerged from a motivation to learn about death, perhaps fuelled by a curiosity about the unique circumstances." They also note, "The fact that Noel preferred to stay close to Thomas over traveling to the high-quality food being offered by the caretakers furthermore casts doubt on the interpretation that Noel cleaned Thomas’ teeth merely to obtain food."

Van Leeuwen and his colleagues also write, "Death responses represent core features of human civilization, with great diversity in mortuary rites found across cultures¹⁶. In general, for animals critically depending on group living¹⁷, like humans and chimpanzees, responding to death may be a means to reorganize the social unit, especially when so-called 'brokers' die: individuals who play an important role in maintaining group cohesion by connecting sub-groups^18,19." (The numbers refer to references in their paper.)

These novel observations show why the study of animal behavior is so fascinating and also show how much we still have to learn about what other animals do and why they do it. How Noel's behavior contributes to our learning more about the evolutionary origins of death responses on humans remains to be determined. Perhaps it has little or nothing to do with what humans do. But let's hope it will open doors for further studies that show that we are not so unique in how we respond to death and other situations.

I look forward to more research in this area of study. We really don't know all that much about what chimpanzees or other nonhuman animals think about death or what they know about the passing of another individual. Please stay tuned for more discussion of this incredibly interesting topic.

Note 1: Boesch, C., Bolé, C., Eckhardt, N. & Boesch, H. Altruism in forest chimpanzees: the case of adoption. PLoS One 5, e8901 (2010).

^{Marc Bekoff’s latest books are Jasper’s Story: Saving Moon Bears (with Jill Robinson), Ignoring Nature No More: The Case for Compassionate Conservation, Why Dogs Hump and Bees Get Depressed: The Fascinating Science of Animal Intelligence, Emotions, Friendship, and Conservation, Rewilding Our Hearts: Building Pathways of Compassion and Coexistence, and The Jane Effect: Celebrating Jane Goodall (edited with Dale Peterson). The Animals’ Agenda: Freedom, Compassion, and Coexistence in the Human Age (with Jessica Pierce) will be published in April 2017 and Canine Confidential: An Insider’s Guide to the Best Lives For Dogs and Us will be published in early 2018. His homepage is marcbekoff.com}