Mutual Mate Choice Can Drive Costly Signaling Even Under Perfect Monogamy

Models of sexual selection by mate choice have emphasized the evolution of sexually dimorphic costly signals, such as elaborate plumage or courtship display, in the sex exhibiting higher reproductive skew, usually males. Less well explored is the action of mutual mate choice in driving signal evolution in socially monogamous or near-monogamous populations. We present a simulation model of condition-dependent investment in a signal trait under conditions of perfect monogamy, equal initial offspring number, and differential offspring mortality based on inherited genetic quality minus signal cost. The model demonstrates persistent evolution of high-cost sexual ornaments through mutual mate choice, even under strict monogamy, as long as the phenotypic condition is sufficiently heritable, and the monomorphic ornament reflects condition with sufficient accuracy to allow positive assortative mating. We discuss implications for research on sexual selection, mate choice, mutation-selection balance, and human evolution.