For Chimps, This Small Gesture Is a Big Deal

It was just a small gesture, but it spoke volumes.

Researchers were watching two chimpanzees in Kibale National Park, Uganda. Adult female Fiona was sitting with her mother, Sutherland. Fiona was grooming her mother when she stopped to take a small leaf from a nearby tree. When chimps are grooming each other, they sometimes pluck leaves and touch them with their mouths or fingers as if they are grooming them. Researchers aren’t exactly sure why they do it, but it’s a common practice.

In this particular situation, Sutherland wasn’t paying attention while her daughter groomed the leaf. Fiona held it out to Sutherland and then moved her arm when she didn’t quickly get a response. Once Sutherland looked toward the leaf, moving her head and eyes toward it, Fiona withdrew the leaf and continued working on it.

While it might seem like an innocuous encounter, researchers were excited. The exchange was an example of “referential gesturing,” where an individual uses a gesture to draw another’s attention to something. In this case, the chimp was showing the leaf just for the sake of sharing something. Until now, that was believed to be something only humans do.

“We assumed that the ability and motivation to show others things simply for the sake of sharing evolved in the human lineage after we diverged from our last common ancestor,” study author Katie Slocombe, a psychology professor at the University of York in the United Kingdom, tells Treehugger.

“Our observations suggest that chimps also do this in specific circumstances, it seems likely that the ability might have been present in our last common ancestor, so the question then changes from how did this ability and motivation arise in the human lineage, to, what selection pressures made humans engage in this behavior at much higher frequencies.”

Slocombe and other researchers were observing chimpanzee mothers and infants as part of a large study on early communication and joint attention.

Looking for Explanations

After capturing footage of the sharing encounter, researchers analyzed 80 similar leaf-grooming experiences to see if there was another explanation for the behavior they saw with Fiona and Sutherland.

“We examined 84 other leaf grooming events to see if the leaf is ever given to onlookers, or eaten (it’s not, so it's unlikely an attempt at food sharing), or if it's used habitually to request grooming or play from others (and we found little evidence of this),” Slocombe says.

“Instead, we found that in the majority of events another individual paid close visual attention to the leaf being groomed, making it likely that this simultaneous attention on the leaf is what Fiona was likely hoping to achieve with her mother (given her mother had ignored her leaf grooming until she showed her the leaf).”

The findings were published in the journal Proceedings of the National Academy of Sciences.

Researchers say they are continuing to study chimp interactions to see if they can find other examples of the animals showing these sharing behaviors.

They say the findings could further the understanding of how human social cognition evolved and what makes the minds of humans unique.

Slocombe says, “We hope the publication of this observation will encourage other researchers to look out for other examples in the future or to find examples from their video archives that they had maybe overlooked.”