Slime mould. 60 000 tiny agents, each one only able to smell the trail in front of it, turn towards the strongest scent and leave a little of their own. Nobody plans anything, yet veins appear and link the food sources with networks as efficient as a railway: in 2010 a slime mould rebuilt the Tokyo rail map this way. Click to drop food · the cursor is food too.
Slime mould
A single-celled organism with no brain that still finds efficient networks.
How it works
Many small agents. Tens of thousands of points crawl over the dish. Each one can only smell the trail just ahead of it, turns towards the strongest scent and lays down a little of its own. Trails that are used get stronger; the rest evaporate.
Networks without a plan. From these local rules, veins appear and join the food sources. In 2010 Atsushi Tero and colleagues placed oat flakes in the shape of the cities around Tokyo, and the slime mould Physarum polycephalum grew a network much like the real railway.
The model. This is Jeff Jones’s 2010 agent model of Physarum. Changing how far the agents smell, or how widely they look, turns the same rules into thin webs, thick rivers or restless loops.