Men think they’ve got it rough finding love. Oh, bars are the wooorst place to meet women. And the drinks are sooo expensive. But in the animal kingdom, the males got it easy. The true burden lies with the female, who expends enormous energy producing eggs and, in the case of mammals, bearing and looking after the young. But what if you’re a hermaphrodite, like some species of marine flatworms? Who’s going to bear the maternal burden there?

Whoever loses the bout of penis fencing, that’s who. In coral reefs, certain species of flatworm do battle with their members.