Their genes are your environment
Peromyscus maniculatus, PeroMHC
When we start accounting for all the things that influence your behavior, the first basic division is between differences in genes and differences in environments.
But environments are not gene-free: your environment if filled by the genes of everyone you interact with. These are termed indirect genetic effects (IGEs, Moore 1997).
Wilson et al. set up a series of bouts between absolutely adorable deer mice (Peromyscus maniculatus). They modeled the factors influencing each animals aggression, starting with their and their opponents identities and then breaking this down into additive genetic and permanent environment effects (the later including non-additive genetic effects as well as early experiences that shaped each animal's aggressiveness). Finally, they added an indirect genetic effect from the opponent to the model. They found
in general, those genotypes that directly cause higher than average aggression in the focal individual also increase the aggressive response indirectly when expressed in the opponent.
Moore et al. Interacting phenotypes and the evolutionary process: I. Direct and indirect genetic effects of social interactions. Evolution (1997) vol. 51 pp. 1352-1362
Wilson et al. Indirect genetic effects and the evolution of aggression in a vertebrate system. Proc R Soc B (2008) doi: 10.1098/rspb.2008.1193
