Inclusive fitness for the conflicted individual

The theory of inclusive fitness explains the process and purpose of social adaptation. However, the canonical derivation of inclusive fitness assumes a simple causal relationship between genotype and phenotype. In reality, different components of the genotype may have different impact upon the phenotype and different genetic relatedness to social partners, as for example in the case of parent-of-origin effects that have been implicated in the evolution of genomic imprinting and a diversity of pathological phenotypes. Whilst such scenarios may be framed in terms of a clash of inclusive-fitness interests of different genes or different genetic factions, it remains unclear whether and how an individual's inclusive fitness may be defined in the context of such internal conflicts. Here, I investigate how the derivation of inclusive fitness is affected in the context of an individual suffering from internal conflict between her maternal-origin versus paternal-origin genes. I show that, in relation to a single conflicted trait, the individual's inclusive fitness is given as a weighted average of the interests of the underlying genetic factions, with the power wielded by each faction providing the appropriate weight. This reveals that internal conflict per se does not erode the adaptive integrity of the individual. Rather, it is variation in the underlying balance of power across different traits that leads to a breakdown of the individual's unity of purpose.