Overview

• Kanzi, a language-trained bonobo, kept mental tabs on two familiar caregivers who hid behind different panels and identified their locations when shown a photo prompt.
• In a separate test, he matched each caregiver’s voice to the correct hiding spot after hearing a brief greeting, performing above chance overall and especially well with one caregiver.
• The study, led by Johns Hopkins University’s Social and Cognitive Origins Group, provides controlled evidence that apes can track multiple individuals who are out of view.
• Authors interpret the results as evidence for integrated vocal–visual–spatial memories shared with humans, with findings published in Proceedings of the Royal Society B (DOI: 10.1098/rspb.2025.0640).
• Researchers plan follow-up work to probe how many individuals apes can track at once and how long such memories last, though further testing cannot include Kanzi, who died in March 2025.