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Abstract: Mutualism and competition are simultaneously at play between a variety of taxonomic categories such as plants and soil microorganisms. Quite generally, this implies tradeoffs and the existence of optimal resource allocations. The carbon and nitrogen cycles in plant-microbe communities provide a classic example in which that optimization can be explored with relatively well-validated models. These yield an optimal outcome for nitrogen allocation between microbes and plants, and this theoretical outcome appears, empirically, to be where nature sits. How might this have evolved? Kin selection is inapplicable, and more generally, from a selfish gene perspective this outcome is impossible. I show, however, that group selection in a patchy environment provides an evolutionary mechanism for attaining this seemingly altruistic outcome. Mutualism and competition are ubiquitous in human society, so what are the societal implications of these findings? I discuss some examples and sketch an agenda for further analysis.