The usual tradeoff for guys

You've heard the quip that God gave men two wonderful organs, a brain and genitalia, but not enough blood to operate both of them at the same time?

Nature imitiates humor. (Hat tip: Soccer Dad)

Best line from the article, which is linked by Secular Blasphemy, is this: "'Bats invest an enormous amount in testis, and the investment has to come from somewhere. There are no free lunches,' said Hoskens, who did not participate in the study."