Pleiotropic "win-win" mutations can rapidly evolve to promote cooperation.

In a well-mixed environment we evolved engineered yeast cooperative communities where two strains exchanged costly metabolites, lysine and hypoxanthine. Among cells that consumed lysine and released hypoxanthine, ecm21 mutations repeatedly arose. ecm21 is self-serving, improving self’s growth rate in limiting lysine. ecm21 is also partner-serving, increasing hypoxanthine release rate per lysine consumption and the steady-state growth rate of partner and of community. ecm21 also arose in monocultures evolving in lysine-limited chemostats.

elifesciences.org/articles/57838