Say you were a female African bat bug. When you’re not sipping the finest of bat blood, you keep busy trying to avoid sex. It’s not that you’re an unhip sex-negative bat bug, it’s just that sex involves a large sharp penis-spear being shoved into your abdomen. Talk about penetration! Of course, it’s not just a girly problem – the male bugs go about shoving their penises into each other’s abdomen too. What with the pain and the infection and the death, it’s not the most comfortable way to perpetuate the species.
To solve this, female bat bugs evolved external genitalia to guide the “hypodermic probe” (as Nature so delicately puts it) to the least-painful location. Male bat bugs started cross-dressing – by copying the female genitalia, they too could be penetrated in the least-painful location, reducing the woes of male-on-male action. The problem was, cross-dressing male bugs ended up being MORE likely to be penetrated, since they were mistaken for females.
So, to solve this most unmasculine of problems, they developed a manly version of the female genitalia. A “mangina,” if you will. And this solved the males’ problem – they were now distinct from the girls, and were no longer accidentally violated quite so much. The females, seeing this glorious lifestyle free of dire abdominal wounding, decided to cross-dress as well – they started to copy the bug-mangina in order to avoid sex. And it works – females with manly-looking external genitalia have less sex than females with more female-looking bits.
And there the African bat bugs are, locked into a cross-dressing gender war about who has the least sex. It seems a little evolutionary improbable – after all, survival of the fittest usually means survival of whoever breeds the most. I speculate that sex must be so dangerous and painful that it actually reduces the bugs’ lifetime reproductive output – in other words, the bugs that have the least sex have the most offspring.