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New study suggests chimpanzees share for fun

Just one leaf has sparked new questions about human social evolution.

(CN) — Humans have long prided themselves on what sets them apart from chimpanzees, despite sharing 99% of the primate's DNA. Now, in research published Monday in Proceedings of the National Academy of Sciences, chimpanzees appear to exhibit another human-like trait: sharing. 

It's nothing new that chimps share food and grooming tasks — it takes a village. However, the new sharing behaviors noted by researchers from the University of Zurich and the University of New York go beyond survival techniques. Instead, the unique mannerisms observed in wild chimpanzees involve "sharing for sharing's sake" and drawing attention to an item. 

This type of gesture is seen in humans around 10 to 13 months old. For example, a toddler shows their parent a toy or other exciting object to view without implying an invitation to play. Nevertheless, it's an important social development that until now has been touted as distinctly human. 

The scientists observed the behavior in an interaction between a chimpanzee mother and daughter in Kibale National Park, Uganda. While leaf grooming, adult daughter Fiona plucked a leaf. She groomed herself with it for a few moments, then held it out to her mother, Sutherland. Her mother didn't respond, so Fiona repositioned her arm, and Sutherland lifted her gaze to look at the leaf. After her mother saw the leaf, Fiona went back to grooming. 

"She's not offering it for food. She doesn't want her mom to do anything. She just wants them to look at it together, and be like 'Oh, cool, nice!" study co-author Katie Slocombe from the University of New York, told The Guardian

The same group of chimpanzees, the Ngogo community, has been seen gesturing for other purposes. For example, they will point to a spot on their body that needs to be scratched or hold their hands out for one of their peers to hand them something. 

After seeing Fiona and Sutherland, the researchers looked at 84 other instances of leaf grooming to find behavior explanations. If Fiona attempted to share the leaf (and a potential parasite) with her mother for food, the expectation would be for Fiona to let go of the leaf and leave it with her mother. Additionally, the type of leaf is not typically eaten by chimpanzees. There was also no evidence that the leaf implied play or another activity. The action was highly social and shared with another chimp that she has a strong social bond. 

While Fiona's leaf is just one instance of this behavior, it has opened the floodgates of questions about our closest DNA relatives. It implies they may be more social than previously thought — and may even help scientists better understand how human social cognition evolved.

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