- A recent study assessed wild chimpanzees’ use of sticks as a tool, monitoring how chimps of different ages gripped and manipulated the implement to retrieve food from tricky places.
- The study found that older chimps were more adept at choosing the right grip for the task at hand, indicating that chimpanzees, like humans, refine tool-use skills well into adulthood.
- The researchers say this continued development of skills is critical for chimpanzees’ survival in a changing climate, and that it highlights the importance of conservation interventions aimed at supporting the preservation of chimpanzee cultures.
Chimpanzees, like humans, can use a variety of tools to perform tasks such as getting food from hard-to-reach places.
Now, a study published in PLOS Biology has found that, also like humans, chimps continue learning and refining those skills well into adulthood.
This lifelong learning and continual development of skills is critical for the survival of chimpanzees in the wild, says lead author Mathieu Malherbe, from the Ape Social Mind Lab at Marc Jeannerod Institute of Cognitive Sciences in France and the Taï Chimpanzee Project in Côte d’Ivoire.
“Chimpanzees’ ability to extract food [that would otherwise be inaccessible] using stick tools might be essential in times of food scarcity which is happening more and more due to climate change,” Malherbe said in an email to Mongabay.
“Chimpanzees have one of the most diverse tool kit, apart from humans. Conservation projects should be focusing on helping preserving these behavioral traits as preserving this species will help us understand our evolutionary history,” he added.
Researchers trying to understand human evolution have identified tool use as a driving force behind both brain development and the long-term dependency of juveniles in the primate lineage, Malherbe said. Likewise, humans’ ability to learn across our entire lifespan has been credited for our ability to flexibly use a wide array of tools.
The researchers note that while many studies have examined how chimps acquire the skills to use tools, very few have looked at how they develop these abilities across their lifetime, especially in the wild. As a result, there’s limited information on which skills are inborn and which ones are learned, and how that learning happens. With this study, the researchers say they aim to help close this gap.
Over the course of seven and a half years, they monitored three communities of 70 western chimpanzees (Pan troglodytes verus) ranging in age from 1-54 years old in Taï National Park. The animals, though wild, are what’s known as habituated, meaning they’re accustomed to the presence of humans.
This allowed the researchers to analyze 1,460 stick use actions, which they filmed as the chimps attempted to extract high-nutrient food from difficult-to-access cavities. They grouped the different types of tool use into categories such as scooping, pounding, and rotating.
The researchers monitored the precision, power and dexterity with which the chimps used the stick depending on the size of the holes and the type of food, whether honey, insects, bone marrow, nut kernels, or seeds inside pods.
They observed that older chimps were more adept at choosing the most effective way to hold a stick to retrieve food. “Adults, but not non-adults, modulated their behavior to use a more appropriate hand grip to fit action requirements,” the study says.
Where pounding was needed, adult chimpanzees preferred a full hand grip, otherwise known as a power grip. When precision was required in tasks such as insertion, they gripped the stick with their fingers.
The observed tool-holding patterns indicate that a prolonged learning period is necessary for a chimp to become efficient in tool use, the study says.
According to the researchers, the ability of adult chimpanzees to choose the right grip for the right action, something not consistently observed in non-adults, suggests that the necessary understanding of the requirements of a specific task is reached later in chimpanzees’ development process.
Malherbe said research projects such as this are already contributing to the conservation of the species.
Chimpanzees are social animals and, like humans, they pass on skills and behaviors from generation to generation through social learning. As such, destroying their communities through human activities like logging or illegal hunting results not only in their deaths but also the killing of generations of unique cultural traditions.
“Hence the IUCN [International Union for Conservation of Nature] now advocating to preserve not only chimpanzees but also their cultures,” Malherbe said.
Erin Wessling, co-lead of the working group on chimpanzee cultures at the IUCN, the global wildlife conservation authority, said the findings of the study “nicely highlight the complexity of the tool use behaviors seen in the wild.”
“If tool use behaviors allow access to foods that are important to their diet, then we should consider tool use, both complex and simple, an important component of chimpanzee survivability, and therefore, conservation,” said Wessling, who was not part of the study.
Human disturbance can affect tool use expression, Wessling added, pointing to the need for scientists and conservationists to think about how maintaining these behaviors might require conservation approaches that go beyond just making sure that chimpanzee populations persist.
“We should be using these beautiful examples of complex behaviors to adjust our thinking about how we can also ensure a framework is there to ensure these complex behaviors get passed along as well,” she said. “If they then take so long to master, then we must make sure we provide them the time to master them.”
Citation:
Malherbe, M., Samuni, L., Ebel, S. J., Kopp, K. S., Crockford, C., & Wittig, R. M. (2024). Protracted development of stick tool use skills extends into adulthood in wild western chimpanzees. PLOS Biology, 22(5), e3002609–e3002609. doi:10.1371/journal.pbio.3002609
Tool innovation shows cultural evolution at work among chimpanzees
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