Study Shows Big Balls Equals No Brains

Big testicles go with tiny brains, according to a new study of bats. The discovery suggests that a biological trade-off has to be made between brains and sperm. Because of high energy demands, males cannot generate large amounts of both, scientists believe.
In many bat species, females are unusually promiscuous, so natural selection has led to males evolving enormous testicles — at the expense of their brains. Their genitals of some bats make up 8.5 per cent of their body mass.
The testicles of apes range from 0.02 per cent to 0.75 per cent of body mass.
Researchers found the link between testicle and brain size after looking at 334 bat species.
In those with rampantly promiscuous females, pea-brained males with large testicles stood a better chance of having offspring than less-fertile but brainier rivals.
"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," the scientists, led by Dr Scott Pitnick, from Syracuse University in New York, wrote in the journal Proceedings of the Royal Society B: Biological Letters.
However, they found that male bats from monogamous species, in which the female is guarded by a single partner, had relatively large brains.
from The Age