Physarum polycephalum + oat flakes = Tokyo subway map?
Because they couldn't mathematically determine a "perfect" solution, the researchers decided to task the slime mold with a problem human designers had already tackled. They placed oat flakes (a slime mold favorite) on agar plates in a pattern that mimicked the locations of cities around Tokyo and impregnated the plates with P. polycephalum at the point representing Tokyo itself. They then watched the slime mold grow for 26 hours, creating tendrils that interconnected the food supplies.
Different plates exhibited a range of solutions, but the visual similarity to the Tokyo rail system was striking in many of them
[via jetlib express, abstract of full article]