Mathematicians may have found an answer to the longstanding puzzle as to why we have evolved to cooperate

http://www.eurekalert.org/pub_releases/2016-07/uob-rda071916.php

Public Release: 19-Jul-2016
Researchers discover altruism is favored by chance
Mathematicians may have found an answer to the longstanding puzzle as to why we have evolved to cooperate
University of Bath

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An international team of researchers, publishing in the Proceedings of the National Academy of Sciences, has found that altruism is favoured by random fluctuations in nature, offering an explanation to the mystery as to why this seemingly disadvantageous trait has evolved.

The researchers, from the Universities of Bath, Manchester and Princeton (USA), developed a mathematical model to predict the path of evolution when altruistic "cooperators" live alongside "cheats" who use up resources but do not themselves contribute.

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"What we are lacking is an explanation of how these behaviours could have evolved in organisms as basic as yeast. Our research proposes a simple answer - it turns out that cooperation is favoured by chance."

The key insight is that the total size of population that can be supported depends on the proportion of cooperators: more cooperation means more food for all and a larger population. If, due to chance, there is a random increase in the number of cheats then there is not enough food to go around and total population size will decrease. Conversely, a random decrease in the number of cheats will allow the population to grow to a larger size, disproportionally benefitting the cooperators. In this way, the cooperators are favoured by chance, and are more likely to win in the long term.

Dr George Constable, soon to join the University of Bath from Princeton, uses the analogy of flipping a coin, where heads wins £20 but tails loses £10:

"Although the odds winning or losing are the same, winning is more good than losing is bad. Random fluctuations in cheat numbers are exploited by the cooperators, who benefit more then they lose out."