In the eye of the swarm

The Economist has a great article on how computer models of how bees, ants and birds operated in swarms, are being deployed as ‘artificial intelligence’ systems to solve previously unassailable problems.

To be honest, the premise of the piece is a little too grand to be plausible: the introductory paragraph announces “The search for artificial intelligence modelled on human brains has been a dismal failure. AI based on ant behaviour, though, is having some success.”

This is really not true, as artificial intelligence has actually been a great success when applied to limited and well-defined problems. The article really just explains how the study of swarm intelligence has allowed us to tackle a new set of limited and well-defined problems that were previously out of easy reach.

However, it does give some fantastic examples of how swarm behaviour, where the combination of simple individual behaviours can solve complex problems, can be applied to a range of problems:

In particular, Dr Dorigo was interested to learn that ants are good at choosing the shortest possible route between a food source and their nest. This is reminiscent of a classic computational conundrum, the travelling-salesman problem. Given a list of cities and their distances apart, the salesman must find the shortest route needed to visit each city once. As the number of cities grows, the problem gets more complicated. A computer trying to solve it will take longer and longer, and suck in more and more processing power. The reason the travelling-salesman problem is so interesting is that many other complex problems, including designing silicon chips and assembling DNA sequences, ultimately come down to a modified version of it.

Ants solve their own version using chemical signals called pheromones. When an ant finds food, she takes it back to the nest, leaving behind a pheromone trail that will attract others. The more ants that follow the trail, the stronger it becomes. The pheromones evaporate quickly, however, so once all the food has been collected, the trail soon goes cold. Moreover, this rapid evaporation means long trails are less attractive than short ones, all else being equal. Pheromones thus amplify the limited intelligence of the individual ants into something more powerful.


Link to Economist article ‘Riders on a Swarm’.
Link to Wikipedia article on swarm intelligence.

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