The Engineer in the Undergrowth
The organism Physarum polycephalum is not a plant, animal, or fungus. It is a myxomycete, or a plasmodial slime mold, that lives in shady and moist habitats like forest floors. The visible, active stage of its life is a plasmodium: a single, giant cell containing millions of nuclei that can grow to cover several square meters. This bright yellow mass moves by extending tube-like structures and pushing the cytoplasm inside, a process called cytoplasmic streaming. Each part of the plasmodium rhythmically expands and contracts to circulate nutrients and chemical signals throughout the entire cell body. This decentralized network allows the organism to forage for its food of bacteria and fungal spores, reacting to local stimuli to move toward food and away from light or repellents.
This simple organism exhibits behaviors that challenge definitions of intelligence. It can solve mazes, consistently finding the most direct route between two food sources. To do this, it first explores every possible path, then retracts from dead ends and strengthens the protoplasmic tube that forms the shortest connection. It also possesses a form of memory. By leaving a trail of slime, it avoids re-exploring areas it has already searched. Experiments in 2008 demonstrated it can anticipate periodic events; after being exposed to cold pulses every 60 minutes, the slime mold continued to slow its activity at 60-minute intervals even after the pulses stopped.