The Wisdom of Mold
Despite its ability to solve an array of problems, the slime mold was designed by evolution to solve just one problem: how to build an optimal transport network (for its nutrients). So we decided to investigate how the slime mold, when presented with the task of connecting the major urban areas of the United States, would design a transport system. Would its design resemble that of the United States highway system, or would the slime mold propose a superior one?
Here’s how our experiment worked. As we detail in a forthcoming article in the journal Complex Systems, we took a large dish in the shape of the United States and placed rolled oats (a food for the slime mold) in the locations of 20 major urban areas. Then we put the slime mold on the rolled oats representing the New York area. The slime mold propagated out from New York toward the other urban areas and eventually spanned them all with its network of protoplasmic tubes. We performed this experiment a number of times.
What did the resulting network look like? It looked remarkably like the United States interstate highway system.
We found that the slime mold approximated almost all interstates. Links from Dallas to Houston, from Chicago to Milwaukee and from New York to Boston were reproduced by the slime mold in almost all experiments. We also found that in three out of four experiments, the slime mold approximated the routes from the San Jose, Calif., area to Las Vegas; the chain of links connecting Denver to Albuquerque to the Phoenix area to the Los Angeles area; and the chain of links connecting Kansas City, Mo., to Oklahoma City to the Dallas area to the Houston area.
It also approximated two chains — one connecting Milwaukee to the Chicago area to Nashville to Memphis; the other connecting Boston to the New York area to Charlotte, N.C., to Atlanta to Jacksonville, Fla. — that are bridged by a link from the Chicago area to New York. (Routes that weren’t approximated were those directly connecting Denver to the San Jose area, the Houston area to Albuquerque and Jacksonville, the New York area to Nashville, and Boston to the Chicago area.)
From the slime mold’s point of view, Interstates 10 and 20 represent the core backbone of the United States transport network: when these interstates are removed, the network separates into disconnected western and eastern parts.