The article by Ryan (1999) examined female mating preferences. Ryan (1999) described female preferences as an influence on male traits and behaviors. Ryan (1999) pointed out that historacle influence of what females prefer can bias male traits. Past studies have examined specific phenotypes that are involved in sexual selection, and how they have evolved, but Ryan (1999) questioned whether or not such traits are adaptive. Ryan (1999) wanted to examine the female side of this relationship. He wanted to know why females have a preference for specific phenotypes.
“Sexual selection by female choice can explain why males evolve such elaborate traits. These males have increased mating success because of their enhanced attractiveness…But why do preferences for these traits evolve” (Ryan, 1999, p. 2)? Females do have preferences that are favored by natural selection. Some preferences that they have may influence their immediate reproductive success. However, there are preferences that do not influence reproductive success (Ryan, 1999). Understanding the evolution of those traits were challenging. Ryan (1999), suggested that past influences of evolution on how females perceive their world can bias the male traits they now find attractive.
Runaway sexual selection and good genes selection are two hypothesis examined by Ryan (1999). They state that “preferences evolve indirectly because they are genetically correlated with male traits that are under direct selection; that is, the preferences themselves are not under direct selection” (Ryan, 1999, p.2). Meaning, female preferences and male traits co-evolve through genetic correlation. (Ryan, 1999).
Sensory exploitation was another, more recent, theory that was examined. It suggests that, “instead of preferences and traits coevolving through a genetic correlation, biases in the female’s response to stimuli favor the evolution of certain male traits. Thus the receiver biases result in preexisting preferences, and males that evolve traits that exploit these preexisting preferences are favored by sexual selection” (Ryan, 1999, p.2). According to this theory, receiver biases are incidental consequences instead of evolved functions (Ryan, 1999). Examining the Platyfish and the Swordtales, which are of the same genus, can see an example of support for this theory. Though they are from the same genus, only the swordtales have swords. What they found was that females of both groups prefer males that have swords, even over males of their own genus that do not have swords (Ryan, 1999). “These studies do not support the simple pattern of male traits exploiting preexisting preferences. They do however, suggest that trait evolution and preference evolution are often decoupled in sexual selection, that they need not evolve through genetic correlation, nor are the response properties of the receiver tightly matched to the properties of the signal, as a lock and a key would be matched” (Ryan, 1999, p.3). Later, it was found that females did not however, show any preference between a swordless male and a sworded male if the two had equal body length (Ryan, 1999). But it is not clear if there is any benefit for the females to mate with larger males.
Ryan (1999) then tried to explain the origins of receiver biases. He argued that they could exist in order for a female to identify her own species, and avoid mating with another species. They might have also evolved in an attempt to assess its environment. Finally, biases could have evolved much like an ability to find prey and avoid predators (Ryan, 1999).
In conclusion Ryan (1999) said that it is unwarranted to continue the examination of the runaway sexual selection and good genes models of preference. Ryan (1999) stated that traits and preferences are not tightly match, and there is often a range of stimuli that is not encompassed by the signals of males that can elicit a receiver response. And, “Reciever biases are not random but are determined in part by the history of receiver responses and the more general operating properties of neural and cognitive systems” (Ryan, 1999, p. 6).