Hide and Seek

Humans maintain a mental map of their loved ones’ whereabouts, keeping track of them whether they are nearby or far away. 

Living in dense forests, bonobos and chimps benefit from mentally tracking their friends and family members, too. 

“People think social intelligence is a thing that makes humans unique, that because we have to manage so many different relationships, we might have a range of cognitive tools for doing so that will only be found in an ultra-social species like humans,” Chris Krupenye, author of a new study, said in a statement.  

“Most of us who study apes have a strong intuition that because the social world is so important for them, too, they must, like humans, be keeping track of these critical social partners,” said Krupenye. “They must share with us at least the foundations of our rich social intelligence.” 

To learn more about this, researchers conducted experiments inspired by hide-and-seek with a bonobo named Kanzi: Kanzi watched two familiar caregivers hide behind different objects that blocked them from view. Then, a researcher would show Kanzi a photo of one of the caregivers and ask him to indicate where they were hiding. The test was repeated multiple times with variations. 

The researchers found that bonobos are capable of mentally keeping track of multiple humans at once, even when they are out of sight. 

“Kanzi very quickly understood the task and performed well,” said study author Luz Carvajal in the statement. 

Then, the team changed the experiment to see if Kanzi could identify the caregivers by the sound of their voices. 

The caregivers hid behind barriers without letting the bonobo see where they were hiding. Once hidden, they each said, “Hi Kanzi,” so he could hear where the sound was coming from. Afterward, the experimenter showed Kanzi a photo of one of the caregivers asking him to point to where they were. 

“Here he also performed (beyond a lucky guess) and especially well with one of his two caregivers,” Carvajal said. “He does have the capacity to use voice as a marker for identity. This face matches this voice.” 

Despite some mistakes, the results show Kanzi’s core ability to mentally track and distinguish the locations of multiple familiar individuals at once. 

Previous research by the same team had already discovered that bonobos and chimpanzees can remember the faces and vocalizations of familiar groupmates they haven’t seen in many years. 

This new study is the first to test if bonobos can track multiple individuals at the same time in a controlled environment, confirming hypotheses from field research. 

“Across these studies, the results suggest that Kanzi has a memory of these individuals that brings together their vocal and visual identities,” said Krupenye. “If he hears them, he might imagine what they look like. If he sees them, he might bring to mind an idea of what they sound like. We think this is one integrated memory.”