Big brains mean 'tiny testicles' 
From: By Nick Buchan
December 07, 2005
Age-old argument ... scientists say size does count / file WOMEN have suspected it for millennia, and scientists have finally proved it - men cannot have both big brains and big testicles. 
Brainiacs and scholars everywhere may gnash their teeth, but according to a recent study of bats, nature forces the males of a species to make a painful trade-off between mental capacity and sperm production.
Because of the high-energy demands of both brains and sperm, scientists believe males cannot generate large amounts of both.
Bats were ideal subjects for the study. Some female bat species are unusually promiscuous, so natural selection led to males evolving enormous testicles in order to compete with more virile suitors - however at the expense of their brain capacity.
Male bats from less promiscuous species, in which the female is guarded by a single partner, had relatively large brains.
While ape species feature testicles ranging from 0.2 to 0.75 per cent of their body mass, certain types of bats boast testicles up to 8.5 per cent of their mass.
The scientists, from New York's Syracuse University, believed this phenomenon is explained by their "expensive tissue" hypothesis.
"Because relatively large brains are metabolically costly to develop and maintain, changes in brain size may be accompanied by compensatory changes in other expensive tissues," wrote Dr Scott Pitnick in the journal Proceedings of the Royal Society B: Biological Letters.
The researchers believed this theory would explain the brains/sperm trade-off found in bats.
"Relatively small brains were found in species that have females that mate promiscuously, are polyandrous and assemble in multi-male/multi-female roosts," wrote the scientists.
"Male promiscuity, by contrast, had no evolutionary influence on relative brain dimension."
Despite these findings however, intelligent males should not despair. While the "whether size matters" debate over may have been settled, the "quality over quantity" battle is just heating up.
