File this under: things to mention at dinner parties when describing what biologists do.

This week's Nature has an news item on an article on earwig penises (penii?). Some species apparently have two, but (obviously?) use only one at a time. But which penis to use? Some species switch it up, but some are right-penised (i.e. they prefer to use the one on the right). The paper proposes an evolutionary scenario for how the single-penised earwigs evolved from the doubly-endowed ones--through a step in which the behavioral preference for the right penis led to loss of the unused left penis (see the figure).