From Darwin to the present day, explaining certain adaptations proves vexing. Darwin proposed sexual selection to explain what otherwise seem like counterproductive traits such as gaudy male adornments, or outlandish breeding rituals. Sex ratio theory poses the problem of the cost of males. Surely a population of hermaphrodites could outbreed one with males by two to one? These hard-to-explain traits represent a class of natural selection known as frequency-dependent. The value of a given trait to an individual depends upon the traits possessed by others within the population, or even the traits possessed by other species, predator-prey coevolution for instance. While unavailable to Darwin, game theory – the mathematics for finding one’s own best strategy when this best strategy depends upon the strategies of others -- is uniquely suited to determining the logic behind all traits subject to natural selection, particularly those under frequency dependent selection. Conceptually, I aim to address three questions: 1) how is natural selection a game?, 2) is game theory scalable from individuals, to populations, to species interactions, and to whole communities in time and space?, 3) what can game theory tell us about such diverse topics as biodiversity, ecosystem services and even cancer.
As a game, individual organisms are the players, their heritable traits the strategies, their fitness consequences the payoffs, and the ecological setting determines the rules. As a game, the ecological and evolutionary dynamics of natural selection drive traits to either peaks or valleys of the adaptive landscape. As peaks, the strategy that maximizes fitness given the circumstances is a no regret strategy or Nash equilibrium. No individual can gain in fitness by unilaterally changing its strategy. This is a key element of the evolutionarily stable strategy. Adaptations are first and foremost Nash. As valleys, the evolutionary dynamics may lead to speciation (evolutionary branching) and form the basis for adaptive radiations. Evolutionary game theory is scalable from individual interactions to whole ecosystem processes. What we see in nature is likely a dull subset of what is evolutionarily feasible and ecologically acceptable. And, Dobzhansky’s observation can be modified to read: nothing in evolution makes sense accept in light of ecology. We can see this in three applications: 1) differences in the structure and biodiversity of coevolved versus invasion structured communities, 2) effects of predator-prey games on material cycling and ecosystem services, and 3) the understanding and treatment of metastatic cancer.