Given a choice of two males, female túngara frogs will select the most attractive — those with calls of a low frequency and long duration. But when a third male who is inferior is added to the lineup, researchers have found, females often choose the less attractive of the first two. In a study published in the journal Science, scientists at the University of Texas, Austin, and at the Smithsonian Tropical Research Institute suggest that when a social situation becomes too complex, obvious decisions become too burdensome for the frogs. A similar effect has been observed in humans, suggesting that irrationality in mate selection may have deep biological roots.