Bacteria and lizards too can play Rock-paper-scissors!

Game Theory provides the foundation for understanding competition in industries with a few producers. Simply speaking, it is a study of strategic decision making. There are 2 types of Games: 1 stage or 2 stage. In a 1 stage game, each participant makes all of his choices before observing any choice by another participant. A very common example of a 1 stage game is ‘Rock-paper-scissors’.

Overview

Rock-paper-scissors is a hand game usually played by two people. It is a game based on random selection like throwing a dice or flipping a coin where the two participants need to make one of the three hand gestures randomly – rock, paper and scissors. Rock represented by clenched fist; paper represented by an  open hand, fingers touching and the third gesture, scissors, represented by two fingers extended and separated. The objective is to select a gesture which defeats that of the opponent. The rules of the game are- The "rock" beats scissors, the "scissors" beat paper and the "paper" beats rock; if both players throw the same shape, the game is tied.

We are not alone to play Rock-Paper-Scissor !

And we thought only kids play it right! Well the amazing thing is nature has evolved its own strategies to make use of this game. Certain species in nature use this game to allow each of the genetic variants to co-exist with equal advantage. Two such species are known to us- Common side-blotched lizard and certain bacterial species but nature may have many such species which use this strategy for survival which are yet unknown to man.

Common side-blotched lizards have evolved a very interesting adaptation to allow all of its genetic variants/morphs to equally survive. And how does it do that? Well by using our very own rock-paper-scissors game in mating! Male side-blotched lizards exhibit distinct throat colorations, and can be divided into three different categories – orange, blue, yellow. Orange-throated males are very aggressive with lots of females in a big territory. Blue-throated males are less aggressive and guard a single mate in a small territory. The yellow-throated males are particularly clever – they can mimic side-blotched females. Thus by feigning as a female they can sneak into others territories, particularly orange-throated males, and steal their mates. Similar to rock-paper-scissor games, orange beats blue, the orange-throated males being more aggressive. Blue beats yellow as it guards only one female, they are better at catching yellow-throated sneaks. Yellow beats orange, the yellow males can easily mimic as a female and enter into the orange-throated males’ territory and steal mates. Just as in the rock-paper-scissors game, each sexual strategy has advantages over one competitor and a vulnerability to another, so that all strategies have a reasonable chance of prevailing.

The same survival strategy is also used in certain bacterial species too. They exhibit a rock-paper-scissors strategy when they engage in antibiotic production which again allows different genetic variants to co-exist. This is how the rock-paper-scissors game strategy is used - antibiotic-producers defeat antibiotic-sensitives; antibiotic-resisters multiply and withstand and out-compete the antibiotic-producers, letting antibiotic-sensitives multiply and out-compete others; until antibiotic-producers multiply again. Thus the cycle continues and each of the genetic variants has equal opportunities at survival.

With these examples, we can see that nature has up its sleeve its very own rock-paper-scissor game to allow for the co-existence of various genetic variants.

Conclusion

                There have been programming competitions for algorithms that play rock-paper-scissors. Algorithms based on Markov Chains have been developed for its strategy. Also there has been a World Body for this game which standardizes the set of rules for international play, called World Rock Paper Scissors Society. And yes, there are international tournaments for this game, which apart from attracting widespread media attention and participants, have also been broadcast live on TV. And we thought it was a kid’s game.

References

Alonzo, S.H.; Barry Sinervo (2001). "Mate choice games, context-dependent good genes, and genetic cycles in the side-blotched lizard, Uta stansburiana". Behavioral Ecology and Sociobiology 49 (2-3): 176–186

About the Author

Sayantan Das is a PGDM student of 2013-2015 batch. He can be reached at sayantand2015@email.iimcal.ac.in

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