types. Once these cells are released, they are independent and tasked with finding another cell it is able to fuse with. Other P. polycephalum may contain different combinations of the matA, matB, and matC genes, allowing over 500 possible variations. It is advantageous for organisms with this type of reproductive cell to have many mating types because the likelihood of the cells finding a partner is greatly increased. At the same time, the risk of inbreeding is drastically reduced. Behavior Similarity to Neural Systems Slime molds share some similarities with neural systems in animals. The membranes of both slime molds and neural cells contains receptor sites, which alter electrical properties of the membrane when it is bound. Therefore, some studies on the early evolution of animal neural systems are inspired by slime molds. When a slime mold mass or mound is physically separated, the cells find their way back to re-unite. Studies on Physarum polycephalum have even shown an ability to learn and predict periodic unfavorable conditions in laboratory experiments. John Tyler Bonner, a professor of ecology known for his studies of slime molds, argues that they are "no more than a bag of amoebae encased in a thin slime sheath, yet they manage to have various behaviors that are equal to those of animals who possess muscles and nerves with ganglia – that is, simple brains." Traffic System Inspirations Atsushi Tero of Hokkaido University grew Physarum in a flat wet dish, placing the mold in a central position representing Tokyo and oat flakes surrounding it corresponding to the locations of other major cities in the Greater Tokyo Area. As Physarum avoids bright light, light was used to simulate mountains, water and other obstacles in the dish. The mold first densely filled the space with plasmodia, and then thinned the network to focus on efficiently connected branches. The network strikingly resembled Tokyo's rail system. Slime mold P. polycephalum was also used by Andrew Adamatzky from the University of the West of England and his colleagues world-wide in experimental laboratory approximations of motorway networks of 14 geographical areas: Australia, Africa, Belgium, Brazil, Canada, China, Germany, Iberia, Italy, Malaysia, Mexico, the Netherlands, UK and US. The filamentary structure of slime molds such as P. polycephalum forming a network to food sources is similar to the large scale galaxy filament structure of the universe. This observation has led astronomers to use simulations based