Narrator: This is Science Today. When it comes to the selection of mates by females of an animal species, the role of parasites may be instrumental. Marlene Zuk, a professor of biology at the University of California, Riverside, has demonstrated that the ornamental and showy plumage of many male birds may indicate to a female that the male she's choosing is of high genetic quality.
Zuk: The idea is pretty straightforward - if a female is going to evaluate a males and see what kind of traits are going to make a good mate, the best thing that she could do would be to evaluate his resistance to disease.
Narrator: In a study, Zuk let the female choose between two roosters - one with parasites and one without.
Zuk: The female would choose the one that was not parasitized more often than not and she would also use the same traits that the parasite affected a lot. The traits that were particularly subject to being smaller or less colorful or whatever when the bird was parasitized, to make her male choice decision.
Narrator: For Science Today, I'm Larissa Branin.