The institute owes its existence to an unlikely partnership forged in postwar Japan. Kinji Imanishi of Kyoto University had pioneered the field study of nonhuman primates in their natural habitats, trekking into forests to observe monkeys as social beings rather than laboratory specimens. Meanwhile, at Tokyo University, Toshihiko Tokizane was pushing the boundaries of brain science, initiating experimental primate studies that probed the neural architecture behind behavior. The two camps differed in method and philosophy, yet both recognized that Japan needed a dedicated national center. In 1964, Nobel Prize-winning physicist Shin'ichiro Tomonaga lent his considerable prestige to the cause, writing directly to Prime Minister Hayato Ikeda to recommend the establishment of such an institute. Three years later, in 1967, the Primate Research Institute opened its doors as part of Kyoto University, deliberately sited not on the Kyoto campus but in Inuyama, beside an existing monkey center that the Meitetsu railroad company had helped establish as a tourist attraction in 1956.

The institute's most famous resident was a chimpanzee named Ai. Arriving as a young chimp in 1977, she became the subject of the Ai Project, a decades-long study led by primatologist Tetsuro Matsuzawa that explored the cognitive boundaries between humans and great apes. Ai learned to identify more than 100 Japanese kanji characters, discriminate all 26 letters of the Roman alphabet, and use Arabic numerals to represent quantities. Her son Ayumu later stunned researchers by outperforming human university students on short-term memory tests involving number sequences flashed on a screen. Ai also painted and drew in her spare time, creating art without any food reward, simply for the apparent pleasure of it. One of her paintings was reproduced on a scarf given to primatologist Jane Goodall. Ai died of natural causes on January 9, 2026, at the age of 49, leaving behind a body of research that fundamentally reshaped assumptions about the cognitive divide between humans and other primates.

The institute's setting in Inuyama is no accident of bureaucratic convenience. The city already held one of Japan's oldest original castles, the 1537 Inuyama Castle, and the surrounding Chubu region offered forested landscapes ideal for primate study. The campus itself is substantial: a five-story main building houses administration, a library, and research departments, while a separate three-story building serves the Center for Human Evolution Modeling Research, established in 1999. A five-story Ape Research Annex and a guest house accommodating about 30 visiting scientists complete the complex. Beyond Inuyama, the institute maintains field stations across Japan, including the famous Koshima station in Miyazaki Prefecture where Imo's sweet-potato washing was first observed. Each year, roughly 170 outside scientists take advantage of the Cooperative Research Program, making it one of the most internationally connected primatology centers in the world.

The institute's story has not been without controversy. In 2020, Kyoto University revealed that research funds had been misappropriated during Matsuzawa's tenure as director from 2006 to 2012, involving the construction of chimpanzee facilities. The scandal led to Matsuzawa's dismissal and triggered a broader reckoning that ultimately resulted in the university's decision to reorganize the institute. After more than 50 years of groundbreaking primatology, the Primate Research Institute as a standalone entity began to be dismantled. Yet its contributions endure in the scientific record: from demonstrating animal culture on Koshima Island to revealing the numerical memory of chimpanzees, the institute helped build a bridge between human and nonhuman minds that no organizational restructuring can erase.