One of the oldest problems in computer science was just solved by a single cell.

A group of researchers from Tokyo's Keio University set out to use an amoeba to solve the Traveling Salesman Problem, a famous problem in computer science. The problem works like this: imagine you're a traveling salesman flying from city to city selling your wares. You're concerned about maximizing your efficiency to make as much money as possible, so you want to find the shortest path that will let you hit every city on your route.

There's no simple mathematical formula to find the most efficient route for our salesman. Instead, the only way to solve the problem is to calculate the length of each route and see which one is the shortest.

Physarum polycephalum is a very simple organism that does two things: it moves toward food and it moves away from light.

What's worse, performing this calculation gets exponentially harder the more cities are added to the route. With four cities, there are only three different routes to consider. But with six cities, there are 360 different routes that need to be calculated. If you've got a route with ten or more cities the number of possible routes is in the millions.

This makes the traveling salesman problem one of a broad class of problems computer scientists call 'NP hard.' These are problems that get exponentially difficult very quickly, which also includes problems related to hacking encrypted systems and cryptocurrency mining. For pretty obvious reasons, a lot of people are interested in finding ways to solve these problems as quickly as possible.

Keio University's solution is different from the typical algorithmic solutions produced by other researchers, because the scientists used an amoeba. Specifically, the Physarum polycephalum slime mold. Physarum polycephalum is a very simple organism that does two things: it moves toward food and it moves away from light. Millions of years of evolution has made Physarum abnormally efficient at both of these things.