Is Bigger Always Better?

Science  05 Aug 2011:
Vol. 333, Issue 6043, pp. 708-709
DOI: 10.1126/science.1210723

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Darwin was famously puzzled by the length of a peacock's train—what made it so big and so elaborate? The theory of sexual selection provided us with the answer: Females choose males with more exaggerated traits, such as a bigger tail, because they signal benefits for their offspring (1). Recent studies, however, have suggested that this is an oversimplification because the perceptual and cognitive mechanisms underlying female choice may not always lead to larger and more extravagant male traits (2, 3). On page 751 of this issue, Akre et al. offer further evidence that female perception can make a big difference. They show that although female frogs prefer male frogs with longer calls, the females are less able to discriminate between males as their calls become longer, perhaps constraining the evolution of call length. The finding is consistent with Weber's law (4), which holds that as the magnitude of two stimuli increases, a greater difference is required to distinguish between them.