The work by researchers with Johns Hopkins University’s Social and Cognitive Origins Group published today in Proceedings of the National Academy of Sciences.

“The ability to sense gaps in one another’s knowledge is at the heart of our most sophisticated social behaviors, central to the ways we cooperate, communicate and work together strategically,” said co-author Chris Krupenye a Johns Hopkins assistant professor of psychological and brain sciences who studies how animals think. “Because this so-called theory of mind supports many of the capacities that make humans unique, like teaching and language, many believe it is absent from animals. But this work demonstrates the rich mental foundations that humans and other apes share — and suggests that these abilities evolved millions of years ago in our common ancestors.”

Krupenye and co-author Luke Townrow, a Johns Hopkins PhD student, worked with three male bonobos, Nyota, 25; Kanzi, 43; and Teco, 13, all living at Ape Initiative, a research and education nonprofit. During the experiment one of the bonobos would sit with Townrow, facing each other across a table. The bonobo would watch as a second person placed a treat, a grape or a Cheerio, under one of three cups. Sometimes Townrow could see where the treat was going, sometimes he couldn’t. The bonobo could have the treat if Townrow could find it.

Whether or not Townrow saw where the treat was hidden, he’d say, “Where’s the grape?” and then wait 10 seconds. If he’d seen the treat being hidden, during the 10 seconds the ape would usually sit still and wait for the treat. But when Townrow hadn’t seen where the treat was hidden, the ape would quickly point to the right cup — sometimes quite demonstratively.

“Their fingers would point right through the mesh — it was clear what they were trying to communicate,” Krupenye said. “One, Kanzi, who was very food motivated, would point repeatedly in certain phases of the experiment — he’d tap several times to get our attention and was quite insistent about it.”

The work is the first to replicate in a controlled setting similar findings from the wild that suggest chimpanzees will vocalize to warn groupmates ignorant to potential threats, such as a snake.

“We predicted that if apes are really tracking ignorance, when their partners lacked knowledge they would be pointing more often and more quickly and that’s exactly what they did,” Krupenye said. “The results also suggest apes can simultaneously hold two conflicting world views in their mind. They know exactly where the food is, and at the same time, they know that their partner’s view of the same situation is missing that information.”

The team was thrilled to further confirm apes’ mental sophistication.

“There are debates in the field about the capabilities of primates and for us it was exciting to confirm that they really do have these rich capacities that some people have denied them,” Krupenye said.

Next the team will work to more deeply explore the apes’ motivations and how they think about other individuals’ minds.

“What we’ve shown here is that apes will communicate with a partner to change their behavior,” said Townrow, “but a key open question for further research is whether apes are also pointing to change their partner’s mental state or their beliefs.”