Dr. Michael J. Ryan from University of Texas was one of the speakers who gave a talk at the CFI Darwin Day celebration. It was "Sexual Selection, Darwin's Second Great Theory: Why males are dying to mate". A provocative title, somewhat -- and indeed, the idea of sexual selection was thought to be provocative and radical in Darwin's times. To me it was those historical footnotes that made up the main interest of his speech, as the idea itself wasn't new to me.
Sexual selection theory says animals evolve certain traits not because they help them to survive, but because those traits help them to attract mates -- even when doing so runs counter to survival. This helps explain why in some species males and females are so markedly different in their appearance and behavior. This is evident even in humans, if we believe "men are from Mars, women are from Venus" brand of stereotypes. :-) Behavioral differences between men and women sometimes seem so dramatic, they can make you wonder if men and women are from different planets. In the animal realm one of the most striking examples of appearance differences between sexes is a peacock's tail. That tail is what got Darwin thinking that natural selection in itself was not enough to explain how it evolved. How is it that this trait allowed peacocks to survive better? Darwin decided he needed another theory. So he came up with the sexual selection theory.
Often the traits that help males attract mates are also the ones that makes them more likely to die. Such is the case with tungara frogs, which Dr. Ryan has studied at length. The males of this species are more likely to attract females if their calls are more complex. (Here Dr. Ryan amused the audience by imitating tungara frog calls. He had to do it because sound wasn't working in his presentation. This was just as well, because, according to him, he can make frog calls so realistic he can even trick the frogs into conversing with him. Apparently male tungara frogs view conversation as a competitive sport: they respond with calls that are more complex than the ones they hear.)
However, tungara frogs predators, such as bats, also favor males that make more complex calls. So the individuals that are more attractive to females are also more likely to die. Both selection and counter-selection forces play a role in evolution.
Back in Darwin's time people had hard time accepting the notion that sexual selection is driven by females choosing males with particular characteristics. They said, we only need to reflect on human species to realize how ridiculous this idea is. In Darwin's Victorian England women had very little choice in most things. So Darwin's idea at that time was radical.
Dr. Ryan (who, by the way, considers himself a feminist) noted that even these days there's large feminist literature that absolutely rejects the notion that female choice of mates is the driving force of sexual selection (among animals, at least). They are incredibly critical of this idea.
Pictures from Darwin Day can be found in my photo gallery. I will keep adding new pictures in the days to come.
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