Baltimore, United States - August 19, 2025 A bonobo named Kanzi has revealed a remarkable ability to mentally track multiple familiar humans at once, even when they are out of sight. Researchers at Johns Hopkins University’s Social and Cognitive Origins Group conducted hide-and-seek experiments to test this capacity. Two caregivers would hide behind barriers while Kanzi was asked to point to their locations using photos. He also identified caregivers by voice alone, demonstrating a skill never before tested in bonobos. “Kanzi very quickly understood the task and performed well,” said lead author Luz Carvajal. “He does have the capacity to use voice as a marker for identity. This face matches this voice.” Senior author Chris Krupenye highlighted the significance: “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.” Published in Proceedings of the Royal Society B, the study shows that Kanzi integrates vocal and visual identities to maintain mental maps of multiple humans. Even when out of sight, he could recall who was where. “Across these studies the results suggest that Kanzi has a memory of these individuals that brings together their vocal and visual identities—who they are, what they sound like, and where they are in space,” said Krupenye. The team now plans to test how many individuals apes can track at once and the duration of these memories, offering new insight into the social intelligence of our closest relatives. “These animals are rich and complex,” Krupenye said. “Even if we just want to understand ourselves better there’s an urgency to this work and to saving this endangered species.”