Narrator: This is Science Today. It was Charles Darwin who first wrote about female choice in animal mate selection, but biologist Marlene Zuk of the University of California, Riverside, says Darwin's idea of female choice did not sit well with his contemporaries and the idea of female choice dropped away for a long time.
Zuk: It wasn't until I think pretty much the 1960s that people started going back to this. The whole point is, how many genes are you going to leave? You're going to leave genes in the form of offspring - what's going to make that happen?
Narrator: For females of an animal species, that all depends on how many offspring can be physically produced and in many cases, reared.
Zuk: But for the males, what they're limited by is the number of females they can attract to mate with them. And so because of that, you would expect males to in general, compete for access to females because the more they can get females, the more genes of theirs are going to be left in the next generation.
Narrator: Zuk is currently studying the importance of disease resistance in animal evolution. For Science Today, Larissa Branin.