Consider a population in which there are conflicts. Each individual has fitness w prior to the conflict, and its fitness changes after the conflict. The average fitness of an individual is its baseline fitness plus the fitness change resulting from an encounter with another individual, weighted by the probability of such an encounter. For a population with 2 types of individuals, H and D, in proportion p and (1-p) in the population, the fitness wh of type H individuals is dependent upon the fitness change ehh associated with encountering another H individual ( the probability of such an encounter is p), and the fitness change ehd associated with encountering a D individual (the probability of such an encounter is 1-p):