More Balls than Brains
Well, there may be more to the old adage than one might think.

The brainier male bats are, the smaller their testicles, according to a new study. Researchers suggest the correlation exists because both organs require a lot of energy to grow and maintain, leading individual species to find the optimum balance. ... Pitnick and his colleagues had predicted that, in species with promiscuous females, males would require bigger brains in order avoid being cuckolded. So they were surprised to find the opposite: ?Perhaps monogamy is more neurologically demanding.? NewScientist

How many of my tax dollars are spent studying things like this. I make myself think that in order to reduce our dependencies on chemical pesticides, we study the natural answers to infestation in order to better take advantage of it. Still, some intern is getting paid, either directly or indirectly, to hold a bat still and measure its reproductive organs. Someone else is quantifying the promiscuity of the females. A manager type is sitting there racking his/her brain trying to figure out how to keep these people focused and motivated. Someone is mopping the floor too. And all on my tax nickel.
Now, as far as which is more taxing on the brain, I fully understand that a female that sleeps around does not require a lot of thought to bed. I'm no expert at this, but pleasing a monogamous female is far more challenging. You cannot just perform the same tasks over and over to please the same female again and again. You must be creative. You must think.
I've always prided myself on being smart. I was not able to get a degree. The more I learn the more I realize I need to learn. I consistently tested one standard deviation above average on intelligence tests in school. As for the other, ask Nat.

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I heard this story on the BBC. I have to give credit to the announcer who said the words out loud with grace and didn't crack up once. The interview with the expert was professional and I did not hear one jab at the ridiculousness of the subject. The next story though was started out by saying "I don't think I can follow that."