For bats, it seems, size does matter.

Scientists have found that in bat species with promiscuous females, male bats have larger testes and smaller brains, compared with bat species with monogamous females, where male bats have smaller testes but larger brains, the AP reported earlier this week.

The study, conducted by Syracuse University biologist Scott Pitnick, was published in the Proceedings of the Royal Society: Biological Science in December and suggests that large testes -- along with a higher sperm count -- give promiscuous bats an evolutionary advantage. Sacrifice a little gray matter for a little -- well, yeah.

"If female bats mate with more than one male, a sperm competition begins," Pitnick said. "The male who ejaculates the greatest number of sperm wins the game, and hence many bats have evolved outrageously big testes."

It is utterly tempting to make an inappropriate comparison with humans -- but I think I'll stop right here.