The advantage or disadvantage of a trait for its bearer is often conditioned by which traits or behavioral patterns other individuals in the population are carrying. This is most noticeable in evolution of individual behavioral patterns, so it is not surprising that these phenomena were first studied on models of the evolution of behavior. It is necessary to stress that most of the phenomena to be discussed in the rest of the chapter can be manifested in the evolution of totally different traits in sexually reproducing species, including traits exhibited in ontogenesis and consecutively in the adult organisms’ morphology. The expedience or lack of expedience of a certain allele is often determined by which allele is present on the homologous chromosome descending from the other parent (non-additive dominance effects) or which alleles are present in other loci on other chromosomes (non-additive epistatic effects). Considering that the vast majority of these phenomena have been studied on models describing the competition of alternative behavioral patterns, i.e. alternative behavioral strategies, I have decided, according to tradition, to include a large part of the subject in this chapter, although logically it would belong in the chapter on frequency-dependent selection.
The competition of alternative strategies will be studied using the complex mathematical apparatus of game theory. This aspect is explained in detail and from a somewhat different angle in Chapter IV.5.1. Basically, a payoff matrix is created for the competing strategies. This matrix states how an individual – bearer of a particular strategy – will be rewarded when interacting with another individual, again a bearer of a strategy (including the same strategy as in the first bearer). If we are studying competition of evolutionary strategies at an intraspecific level, we can express the size of rewards for the individual participants in the evolutionary game in units of biological fitness. In direct dependence on the average fitness of the bearers, the frequency of the bearers of the individual strategies in the population changes during the game, i.e. from one generation to another. During the evolutionary game, some strategy either finally wins or a balanced state is established when the frequencies of the individual strategies remain stable; eventually, the proportions of the individual strategies may change cyclically. Except for pure strategies, with the individual always behaving the same way in interaction with another individual, mixed strategies are also known, when the individual behaves with probability ofp1 in one way and with probabilities of p2, p3, p4 … pi in other ways, and context- conditioned strategies, when the individual behaves in interaction with another individual according to the strategy of the other one.