David Beckham might wear a sarong and Takuya Kimura of SMAP may sometimes wear lipstick, but in humans, most males are dull compared to the females. In other animals, of course, the opposite is true: it is the males that are showy, brightly colored, flashy.

Biologists have known why this is since Darwin explained the process of sexual selection, the corollary to natural selection that describes how males compete for females and females choose among males. This means that males will often have "weapons," such as horns for fighting, but it also means that they will be as attractive, colorful and pretty as possible, so that females will be more likely to choose them.

What biologists have not known, not for sure, is why females prefer the prettiest, brightest males. Researchers suspected that brighter males were somehow better -- but in what way? Two papers published in Science last week suggest an answer.