If Brad Pitt and Angelina Jolie were guppies instead of people, they may have had to adopt. That's according to new research reported by the BBC, which has shown that the most attractive male tropical guppies tend to have less competitive sperm.

Popular among aquarium owners because of their vibrant colors, guppies are flamboyant fish which engage in a very peculiar evolutionary drama. Australian researchers have revealed that less attractive male guppies have "better sperm" than their more dashing counterparts, suggesting that, for these fish at least, there is a biological trade off between attractiveness and sperm quality.

While some male guppies invest more heavily in their appearance with the hope of attracting more mates, other male guppies invest in spawning faster swimming sperm. According to Professor Jonathan Evans from the University of Western Australia, who carried out the study, the findings support "sperm competition theory".

Originally proposed by British biologist Geoffrey Parker, sperm competition theory is defined as the "competition between sperm of two or more males for the fertilization of an ovum." In the case of guppies, less attractive males who are unable to attract a mate typically try to compensate by performing non-consensual "sneak" matings. They gain an advantage over their flaunty competitors because their sperm is superior.

"Males that predominantly performed sneak matings were less ornamented but had faster swimming sperm than those that predominantly used courtship," explained Evans. "The reproductive advantage enjoyed by attractive males might potentially be offset by the poor performance of their ejaculates during sperm competition."