Image of the Day: When Leftovers Are A Good Thing

The bird that helped Charles Darwin unlock the workings of natural selection are now helping biologists explain a long-standing evolutionary paradox.

Previous research has shown that wild female finches often go for flashier males. Many biologists argue that competition for mates, known as "sexual selection," is the driving force behind this behavior.

But if everyone mates with the same perfect-looking individual, then the population will eventually become inbred. So how do females avoid this unsavory fate while still mating with the most qualified male?

The answer, it seems, all comes down to who's available when a female is ready to breed and the fact that female birds generally leave home to breed, while males stay put and breed near their birthplace.

Early in the breeding season, the available mates aren't genetically diverse but some males are flashy, displaying elaborate and seemingly useless getups to attract a female's attention.

Later in the season, single females that arrive from out of town will find that all the flashy males have been snatched up. These females----which are genetically different from the locals--will be forced to breed with whatever males haven't already been taken. This staggered breeding schedule helps to ensure genetic diversity among the population.

The study, led by Kevin Oh from the University of Arizona, will be detailed in an upcoming issue of the journal Proceedings of the Royal Society B.