Depue & Morrone-Strupinsky (D&M-S) do not address how a reward system accommodates the motivational dilemmas associated with (a) the decision to approach versus avoid conspecifics, and (b) self versus other tradeoffs inherent in behaving altruistically toward bonded relationship partners. We provide an alternative evolutionary view that addresses motivational conflict, and discuss implications for the neurobiological study of affiliative bonds.

We support the ambitious goal of unification within the behavioral sciences. We suggest that Darwinian evolution by means of natural selection can provide the integrative glue for this purpose, and we review our own work on selective investment theory (SIT), which is an example of how other-regarding preferences can be accommodated by a gene-centered account of evolution. (Published Online April 27 2007).