Article Link: http://www.jgore.org/research.html

Evolution, through survival of the “fittest”, is commonly thought of as a very harsh process that results in zero-sum outcomes - one organism thrives at the expense of another. It is also commonly thought that after billions of years of evolution, current organisms are highly efficient at survival.

The observation of cooperation among organisms comes into conflict with these two axioms in evolutionary biology. Jeff Gore at the Physics Department at MIT seeks to understand why cooperation in nutrient consumption exists in yeast.

Glucose and fructose are essential nutrients for yeast to survive, which can be broken down from sucrose by the enzyme invertase. Yeast can survive on sucrose-only growth media by secreting invertase between its plasma membrane and cell wall. Unfortunately, only 1% of the resulting glucose and fructose is transported into the cell, while the remaining 99% is transported out for other cells to use. This explains why the growth rate of yeast increases with cell density, a counter-intuitive observation.

In effect, the production of invertase from a single cell benefits other yeast cells more than the cell that produced the enzyme. Gore and colleagues describe how a “cheater” strain of yeast that doesn’t express invertase can “freeload” off of the normal strains that do, in a relationship described by the Hawk-Dove game - since cells can switch between “normal” and “cheater” behavior, discoordination is favored.

Through transforming the nature of the cooperation game by modulating the nutrients available and the level of cooperation, Gore et al has shown that a wide range of parameters favor the “cheater” strain thriving alongside the normal strain.

This paper gives evidence that in highly efficient biological systems, organisms may actively increase the payoff of others more than it does to itself. Since it exists today, why is this process is biologically favorable? Answering this question may give a more complete explanation of how evolution shapes populations.