Here's a rhetorical question that isn't just an excuse to talk about something rude. Would you men out there rather have large gonads or large brains? For female readers, how about this: What do you think is most important in a male, testes size or brain size?

You might think that it's not a case of one or the other, that it's possible to have large testes and a large brain. Likewise, there might be some unfortunate males with both small testes and a small brain.

But new research in bats suggests otherwise.