When it comes to bats, size matters (CNN) (brains vs testes)

[eppur_se_muova]

SYRACUSE, New York (AP) -- For some male bats, sexual prowess comes with a price -- smaller brains.

A research team led by Syracuse University biologist Scott Pitnick found that in bat species where the females are promiscuous, the males boasting the largest testicles also had the smallest brains. Conversely, where the females were faithful, the males had smaller testes and larger brains.
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The study offers evidence that males -- at least in some species -- make an evolutionary trade-off between intelligence and sexual prowess, said David Hoskens, a biologist at the Center for Ecology and Conservation at the University of Exeter in England and a leading authority on bats' mating behavior.
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Pitnick's research suggested that in those bat species with promiscuous females, the male's body used more of its energy to enhance the testes -- giving it the greater adaptive advantage -- and lacked the energy it needed to further develop the brain.
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more at http://www.cnn.com/2006/TECH/science/01/24/bat.brains.ap/index.html

OK folks, this just confirms everything you always suspected. Have fun with this one!