Game Theory Leads to Monkey Business

Article excerpt

It's great being a scientist. You can sound ever so impressive by telling everyone that you're studying "non-transitive relations". It sounds so much more erudite than "I play rock-paper-scissors for a living".

On 20 June, researchers from the University of Washington published a paper describing a game of rock-paper-scissors, played using three strains of E coli bacteria. One of the strains produces two toxins, both of which kill the second strain.

The third strain is immune to both toxins and multiplies much faster than the producer of the toxins. However, the strain that is sensitive to the toxins multiplies even faster. The result is that their coexistence follows the law of non-transitive relations: A beats B, B beats C and C beats A. Rock-paper-scissors to you and me.

What is so interesting is that these bacteria have evolved restraint. The toxin-resistant strain doesn't multiply too fast, for example, or it will overwhelm the toxin producer, which will allow the toxin-sensitive strain to take over the habitat.

Such situations may be the origin of co-operation across the evolutionary spectrum. While nature is often depicted as "red in tooth and claw", rock-paper-scissors experiments show "my enemy's enemy is my friend" has a role to play, too. Sometimes things are outside your control; when the optimal strategy depends on what someone else does, it makes sense to hold back from delivering a killer blow.

Other scientists have seen the same principle at work. In a population of Californian lizards, for example, males with an orange throat-patch use aggressive behaviour to ward off rivals. But males with a yellow patch sneak up on females, defeating this strategy. …