Researchers and philosophers are locked in a fierce debate over whether apparently simple organisms such as slime moulds should be described as "intelligent" — a dispute that, its proponents say, could change how we understand life and our own cognitive uniqueness.
Toshiyuki Nakagaki, now a leading figure in the field, recalled first encountering a lemon-yellow stain of Physarum polycephalum on a petri dish while he was an undergraduate in Hokkaido. "I was just impressed with how fast it moved," he said, noting that the species can travel at about 1 centimetre an hour — a brisk pace for amoeboid life.
For much of scientific history, slime moulds were regarded as exceptionally simple. One 1895 description called them "a simple mass of protoplasm," and another commentator described them as "among the most simple of organisms." To casual observation, a slime mould can appear little more than a single cell that feeds and reproduces, reinforcing long-held characterisations of simplicity.
In recent decades, however, observations of more complex behaviour have prompted some scientists to argue that these organisms exhibit capacities that merit the term "intelligence," or at least require a reassessment of behavioural and cognitive categories. Others urge caution, warning that applying human-derived labels risks misunderstanding both the biology of these organisms and the meanings of intelligence — a concern captured in the headline framing of the debate as "dangerous" by some critics.
The disagreement is not only academic. How researchers define intelligence affects experimental approaches, comparative studies across species, and broader philosophical views about agency and cognition in the natural world. As the dispute continues, its outcome may alter how scientists and the public think about the boundaries between simple life and minds, and about humanity's place within the spectrum of living systems.