"What we are lacking is an explanation of how these behaviors could have evolved in organisms as basic as yeast," Rogers said. "Our research proposes a simple answer – it turns out that cooperation is favored by chance."
The problem, Rogers' work suggests, is that people were focusing on the individual, not the whole population and making what the authors call; "the unrealistic assumptions of fixed population size". Yeast cooperators make more food available in total, leading to a larger total population size. Rogers' model showed that random fluctuations can lead to an increase in cheaters, in which case the available food supply will not sustain the whole population, causing a crash. On the other hand, a fluctuation that produced more cooperators would lead to more food and a larger population.
Such random changes ensure populations with more cooperators thrive, increasing the chances that those present, the majority of which are cooperators, will migrate to other locations and dominate populations..
First author Dr George Constable of Princeton compared the situation to flipping a coin where heads gives a cooperator twice as much as it loses when the coin lands tails. “Although the odds winning or losing are the same, winning is more good than losing is bad," Constable said. "Random fluctuations in cheat numbers are exploited by the cooperators, who benefit more then they lose out."