Scientists Debate Intelligence in Slime Moulds

Scientists and philosophers are currently debating whether the humble slime mould, *Physarum polycephalum*, should be classified as an intelligent organism—a question that could alter how we view cognition in the natural world. The controversy was sparked by Toshiyuki Nakagaki, an undergraduate in Hokkaido who, forty years ago, noticed a lemon‑yellow stain in a petri dish and became a leading researcher on slime moulds. Nakagaki’s early observations of the organism’s rapid, 1 cm per hour movement revealed that *Physarum* is far from a simple mass of protoplasm; instead, it can sense and navigate toward food sources, extending long protoplasmic filaments that both digest prey and guide further foraging.

Historically, *Physarum* was described as “one of the most simple of organisms,” a characterization that has been challenged by recent studies showing complex decision‑making and problem‑solving abilities. When presented with multiple food sources, the mould can solve mazes, optimize network routes, and even anticipate future food locations—behaviours that mirror basic forms of learning and memory. These findings have prompted biologists to reconsider the thresholds for intelligence, raising questions about the evolutionary origins of cognition and the ethical treatment of simple life forms.

The debate underscores a broader shift in biology, where the line between “simple” and “intelligent” is increasingly blurred. If slime moulds are accepted as possessing a rudimentary form of intelligence, it could prompt a reevaluation of many other organisms traditionally dismissed as lacking cognition. For now, the scientific community remains divided, but the ongoing research promises to deepen our understanding of life’s diverse cognitive strategies.