The Economist summarizes recent publications by Adamatzky and Jones and Atsushi Tero that use Physarum polycephalum, a species of myxomycetes (a/k/a slime mold, probably my favorite simple organisms), to model the tradeoffs between efficiency and redundancy in designing macro networks, like rail lines or motorways.
Of course, neither Dr Tero nor Dr Adamatzky is suggesting that rail and road networks should be designed by slime moulds. What they are proposing is that good and complex solutions can emerge from simple rules, and that this principle might be applied elsewhere.