What chimpanzee gestures reveal about human communication

JULY 26, 2024

By 

Regina G. Barber

, 

Emily Kwong

, 

Ailsa Chang

, 

Rachel Carlson

, 

Kira Wakeam

 

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Two chimpanzees groom each other — a behavior that can involve several gestures.

Anup Shah/Getty Images

Chimpanzees are our closest living relatives. But how much of their communication resembles ours?

A lot, it turns out.

According to a study published Monday in the journal Current Biology, chimpanzees gesture back-and-forth in a similar way to humans taking turns speaking.

Gal Badihi, a postdoctoral research fellow at the University of St. Andrews, looked at exchanges among five wild chimpanzee populations in East Africa. Usually, these exchanges had two parts: One chimpanzee might tap the another's hand, and then the other taps back like in this video

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But sometimes the exchanges had up to seven parts, which was exciting to see.

Badihi told NPR that these chimpanzees "seem to have this back and forth in a face-to-face communicative set up that kind of resembles human conversations."

Sweeping an enormous data set of ape communication, Badihi and the research team determined that 14% of communicative interactions between the chimpanzees involved gestural exchanges.

For example, chimpanzees groom one another, which involves a lot of gestures. One chimpanzee might scratch himself in an exaggerated way, and in response, another chimpanzee may respond with a gesture to clarify where to begin grooming.

"They might also gesture to start traveling together, or when they greet each other after a long time. They even may shake hands or hug or kiss," Badihi told NPR.

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On average, the timing between a gesture and response was 120 milliseconds. Of the various populations, the Sonso chimpanzees of Uganda were the slowest responders. But overall, these interactions happened quickly.

The speed of human conversation is also a rapid-fire volley. Across language, conversational turn-taking averages 200 milliseconds between responses.

The research presents an intriguing possibility: Back-and-forth communication may have evolved before humans split off from great apes.

No language required.

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Today's episode was produced by Rachel Carlson and Kira Wakeam, and edited by Rebecca Ramirez and Christopher Intagliata. Emily Kwong, Regina G. Barber, Rachel and Rebecca checked the facts. The audio engineer was Valentina Rodriguez-Sanchez.

 

Dogs Can Smell Our Stress, And It Affects Them Deeply

HUMANS26 July 2024

ByRUSSELL MCLENDON

(Sarah Cartwright/Flickr)

Dogs can smell human stress, and a new study reveals the scent may trigger a similar emotional effect in dogs, prompting them to make 'pessimistic' decisions.

This is the first scientific evidence of human stress odors influencing emotion and learning in dogs, the UK team of researchers say, and may shed valuable new light on the ancient bond between our species.

While dogs' ability to sense human moods may come as little surprise to those who live with them, the study suggests it's stronger than many people think.

"Owners know how attuned their pets are to their emotions, but here we show that even the odor of a stressed, unfamiliar human affects a dog's emotional state, perception of rewards, and ability to learn," says senior author Nicola Rooney, a human-animal interactions researcher at the University of Bristol.

Previous studies in humans have shown we can sniff clues about other people's emotions, subconsciously detecting chemosignals in their sweat, and these hidden signals can subtly affect our own emotions and decisions.

Dogs also detect these signals from us, as other recent findings show, but Rooney and her colleagues hoped to learn how our stress odors affect them.

Since dogs are skilled at reading human verbal and non-verbal cues, the researchers decided against directly exposing them to stressed-out humans.

Study participant Freddie sits next to a jar containing an odor sample. (University of Bristol)

Instead, dogs were presented with sweat and breath samples collected from three unfamiliar human volunteers as they relaxed or did something stressful.

The relaxing activity involved watching a nature video, while the stress test involved frustrating instructions related to maths and public speaking.

The researchers recruited 18 dog-human duos to participate in trials featuring the human odor samples. The dogs learned during training sessions that a food bowl in one location always contained a treat, while a bowl at a second site was always empty.

Dogs who learned this began to approach more quickly if a bowl was placed in the positive location P (associated with treats) than in the negative one N (associated with no treats).

The dogs' eager scurrying indicates "optimism," the team explains, or a behavioral signal hinting at an animal's emotional state, based on previous research linking people's positive and negative emotions with "optimistic" or "pessimistic" decisions, respectively.

After initial training, the researchers began to serve bowls in new places, cryptically located between the first two, to see how readily dogs approached.

They introduced three new locations, each identified by its proximity to one of the original two sites: near-positive NP, middle M, and near-negative NN.

They repeated these experiments while exposing dogs to odor samples from either stressed or relaxed humans, or to no odor at all.

The experimental layout. (Parr-Cortes et al., Scientific Reports, 2024)

Dogs were significantly less likely to approach a bowl in the near-negative position when they smelled a stressed stranger, than when exposed to the scent of a relaxed stranger or blank cloth.

The stress odor proved less discouraging when a bowl was in the middle or near-positive position, but combined with a placement near the foodless zone, the odor was apparently enough to dampen their hopes.

The same near-negative bowl location didn't seem to dissuade dogs quite as much when they weren't exposed to the stress odor. This suggests dogs were considering ambient odors along with the bowl's position to estimate the likelihood of finding food.

"Working dog handlers often describe stress traveling down the lead, but we've shown it can also travel through the air," Rooney says.

The subdued response from dogs exposed to human stress odor qualifies as pessimism, and hints at a negative emotional state. This may be adaptive, perhaps helping dogs conserve resources or avoid frustration.

Much of this dynamic is still poorly understood, and more research will be needed to clarify how exactly our odors affect the way dogs feel and learn.

And given the broad importance of dogs to humans globally – as co-workers, partners, and friends – we'd be wise to follow clues that might bolster our bond.

"Understanding how human stress affects dogs' well-being is an important consideration for dogs in kennels," says Rooney, "and when training companion dogs and dogs for working roles such as assistance dogs."

The study was published in Scientific Reports.