Ai, a chimpanzee who contributed for many years to Kyoto University’s research on the evolution of mind, passed away peacefully at 4:04 p.m. on January 9, 2026. She died of age-related multiple organ failure, surrounded by many devoted staff members. She was 49 years old.

      It has been 27 years since I first met Ai, and 18 years since we began working together. Nearly my contemporary, she was more than a subject of study—she was a true partner in research. Through her presence, I learned not only about the minds of chimpanzees and what it means to be a chimpanzee, but also about ourselves as humans.
In terms of cognitive ability alone, Ai was not uniquely “brilliant,” nor was she a singular “genius.” With careful methods, other chimpanzees can demonstrate similar capacities. What made Ai exceptional was her deep curiosity and her willingness to engage. She approached a wide range of tasks with remarkable motivation, and in doing so she continually guided us—often silently—toward better questions. The way she worked with us shaped how we designed tasks and how we sought to understand the chimpanzee mind. In that sense, Ai was, without question, a special chimpanzee.
     As she grew older, the form of her curiosity began to change. Her interest gradually shifted from the tasks themselves to the people around her. Even when she came to the laboratory, she often preferred spending time with the researchers to working on experiments. I also remember, with particular warmth, how she came to cherish moments with the caregivers and researchers who brought her meals more than the food itself.
I feel profoundly grateful to have shared so many years with Ai, both as a researcher and as her partner. With deep appreciation for Ai and for all the people who supported Ai, I now hope that she is resting peacefully.
     Thank you, Ai

Ikuma Adachi, PhD

Associate Professor
Behavioral Science Group, Section of Behavioral and Cognitive Neuroscience
Center for the Evolutionary Origins of Human Behavior, Kyoto University