Are high-quality mates always attractive?: State-dependent mate preferences in birds and humans

Abstract

Sexual selection theory posits that females should choose mates in a way that maximizes their reproductive success. But what exactly is the optimal choice? Most empirical research is based on the assumption that females seek a male of the highest possible quality (in terms of the genes or resources he can provide), and hence show directional preferences for indicators of male quality. This implies that attractiveness and quality should be highly correlated. However, females frequently differ in what they find attractive. New theoretical and empirical insights provide mounting evidence that a female's own quality biases her judgement of male attractiveness, such that male quality and attractiveness do not always coincide. A recent experiment in songbirds demonstrated for the first time that manipulation of female condition can lead to divergent female preferences, with low-quality females actively preferring low-quality males over high-quality males. This result is in line with theory on state-dependent mate choice and is reminiscent of assortative mating preferences in humans. Here we discuss the implications of this work for the study of mate preferences.

Keywords: assortative mating; attractiveness; birds; choosiness; condition; constrained and unconstrained choice; humans; preference function; state-dependent mate choice; zebra finch.

Figure 1

Different underlying processes can lead to assortative mating. (A) Divergent, state-dependent preferences in both sexes (high-quality individuals prefer high-quality mates, while lowquality individuals prefer low-quality mates). (B) Uniform, directional preference for high-quality mates in both sexes. Due to mutual choice and competition for mates, low-quality individuals are left with only low-quality mates to pair up with. Low-quality individuals will typically spend more time and energy in finding a mate.