Kanzi the bonobo. Credit: Ape Initiative
New research using hide-and-seek inspired experiments shows for the first time that apes can mentally keep track of multiple humans at once, even if they are hiding.
The findings answer key questions about how animals can keep track of their groupmates and challenges the assumption that these advanced social cognition traits are only found in humans.
Researchers played the games with a bonobo named Kanzi. The endangered species of great ape is smaller and darker than chimpanzees. They are one of the closest living evolutionary relatives to Homo sapiens, sharing 98.7% of their DNA with humans.
“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,” says Chris Krupenye, a senior author of the study from Johns Hopkins University’s Social and Cognitive Origins Group in the US.
“But 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. They must share with us at least the foundations of our rich social intelligence.”
Previous research by Krupenye’s team found that apes can remember the faces of groupmates they haven’t seen in more than 25 years.
Although previous field studies have suggested there may be a possibility that apes can mentally track groupmates, this is the first study to specifically test whether any animal can track multiple individuals at once, in a controlled environment.
Throughout the tests, Kanzi watched as 2 familiar caregivers hid behind different objects that blocked them from his view. A researcher would then hold up a photo of one of the caregivers and ask Kanzi to point to where they were hiding.
The researchers repeated the experiment and switched up the hiding spots. The results are published in the Proceedings of the Royal Society B: Biological Sciences.
“Kanzi very quickly understood the task and performed well,” says Luz Carvajal, a PhD student in Krupenye’s lab and lead author of the study.
The researchers conducted another test where the caregivers hid behind barriers which Kanzi could not see behind. Instead, the caregivers would call out “Hi Kanzi” once hidden so he could hear which barrier they were behind instead.
“He does have the capacity to use voice as a marker for identity. This face matches this voice,” says Carvajal.
“Here he also performed above chance and especially well with one of his two caregivers,”
Kanzi did make some mistakes, but the researchers suggest the results demonstrate a fundamental capacity to remember the locations of multiple familiar individuals at once.
“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,” says Krupenye.
“We think this is one integrated memory. He’s using the same photo prompt to refer to an individual whether he can see them or not.”
The team hopes to continue their research by testing how long apes can remember these memories and how many individuals an ape can track at one time.
“Even if we just want to understand ourselves better, there’s an urgency to this work and to saving this endangered species,” says Krupenye.
“These animals are rich and complex.”