Direct and Indirect Benefits
Being choosy (having a bias in the context of mating) must incur a fitness advantage in order for this behavior to evolve. Two types of fitness benefits (direct and indirect) are thought to drive the evolutionary mechanisms of mate choice.
Direct benefits are those that increase the fitness of the choosy sex through direct material advantages. These benefits include but are not limited to increased territory quality, increased parental care, and protection from predators. There is much support for maintenance of mate choice by direct benefits and it is the least controversial model to explain discriminate mating.
Indirect benefits increase genetic fitness for the offspring. When it appears that the choosy sex does not receive direct benefits from his or her mate, indirect benefits may be the payoff for being selective. Examples of indirect benefits include better genetic quality and more attractive offspring. R. A. Fisher described this less obvious model in a book called The Genetical Theory of Natural Selection. Fisher explained that, through indirect selection, fitter individuals inherit both the genes and the mating preference for some indicator trait. This linkage of an indicator trait and the preference for such trait results in exaggerated phenotypes and is known as Fisherian runaway selection.
Read more about this topic: Mate Choice
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