What aging chimpanzees can teach us about ourselves

As wild chimpanzees grow older, they tend to back away from complex tool-use activities. When they do engage, they become less efficient – paralleling many of the changes seen in aging humans.

This is the central finding of a new study based on an extraordinary 17-year record of wild chimpanzee behavior in Guinea’s Bossou Forest.

Researchers discovered that aging chimpanzees were not only less likely to participate in nut-cracking sessions using stone tools, but those who did often worked more slowly and less effectively than in their youth.

Some individuals appeared to struggle considerably with the task, while others retained strong abilities into their later years. The data suggest that, just like humans, chimpanzees vary widely in how age impacts their technical skills.

Aging chimpanzees slow down

Scientists know much less about how growing older affects wild animals than they do about human aging, which is well studied. This is especially true when it comes to physically and cognitively demanding behaviors.

Elliot Howard-Spink, a postdoctoral researcher at the Max Planck Institute of Animal Behavior, is the study’s lead author.

“Tool use is uncommon among animals, possibly because it requires a suite of physical and cognitive abilities, such as planning, fine motor coordination, understanding causal relationships, and identifying physical properties of objects,” he said.

“Given many of these faculties can be impacted by aging, wild animals’ tool-use behaviors could be vulnerable to decline with old age.”

The team analyzed behavior records from Bossou, where chimpanzees use stones to crack oil palm nuts. The technique involves selecting appropriate hammer and anvil stones and executing coordinated, targeted strikes.

Over the 17-year study period, the researchers focused on five adult chimpanzees – four females and one male – who aged from around 40 to 60 years old during the observation window.

Less interest, lower efficiency

What they saw was a steady decline in nut-cracking activity among the older individuals. Unlike younger adults, older chimpanzees showed a major decline in their attendance at the outdoor laboratory over successive field seasons.

This reduction suggested a gradual disengagement from the demanding foraging behavior. Even when older chimpanzees did show up, some spent noticeably less time interacting with the tools and nuts – further evidence of an age-related withdrawal.

The team also documented changes in performance. Some older chimpanzees took longer to select appropriate tools, switched stones more frequently, or required more attempts to open each nut.

The inefficiencies accumulated: it took more time and more strikes for the older apes to get the job done. But the degree of decline was not universal.

The scientists found stark differences in the magnitude of changes across individuals. Some chimpanzees maintained relatively steady skill levels into old age, while others showed marked decline.

One elder stands out

Susana Carvalho, a group leader at the Research Center in Biodiversity and Genetic Resources (CIBIO) in Portugal recalled a particularly vivid example from a chimpanzee named Yo.

“We first spotted an elderly female (Yo) seemingly experiencing difficulties during nut cracking whilst observing chimpanzees in 2012,” she said. “Yo, formerly a keen and efficient tool-user, was taking a very long time to crack each nut, and was changing the stone tools she was using frequently.”

The long-term data later confirmed those early observations. This deep behavioral record from Bossou is unique because it covers nearly two decades.

The data was gathered in a consistent field setup known as the “outdoor laboratory.” The researchers placed nuts and tools in a clearing and filmed the chimpanzees who came to use them.

“This research was only possible through the unique video archive produced by decades of continuous observation,” said Tetsuro Matsuzawa, the founding director of the Bossou Archive.

“The Bossou Archive offers a baseline to inform conservation strategies across wild chimpanzee populations, including accounting for behavioral changes over lifetimes.”

Chimpanzees mirror aging humans

The study also demonstrates the cultural dimension of tool use among chimpanzees.

“Just as with human technical skills, chimpanzee tool use is culturally learned through social learning and individual practice,” noted study co-author Katarina Almeida-Warren, a researcher at the University of Oxford.

“By studying the same chimpanzees over two decades, we’ve been able to see how chimpanzees’ cultural skills change with old age.”

While the research did not pinpoint the biological mechanisms behind the decline, it opens new avenues for exploring how age affects cognition and behavior in our closest living relatives.

“As ours was an observational study, we can’t yet identify the specific reasons why aging affects nut cracking,” said co-senior author Dora Biro, a primatologist at the University of Rochester.

“But our results raise important questions about how aging influences apes’ cognition and behavior in natural settings.”

Aging changes chimpanzee culture

With its detailed focus on individual animals over many years, the Bossou study provides a rare look at aging outside of captivity or the human species.

It also raises questions about how skill learning, use, and decline might shape not only individual lives but group dynamics and traditions in wild chimpanzee communities.

“Until now, there has been no systematic study of how old age influences the technological behaviors of wild animals,” said Howard-Spink. That’s beginning to change – and the results suggest that even in the forest, age can bring challenges similar to those in humans.

The study is published in the journal eLife.

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