Yesterday a client brought a young male Pit Bull puppy to see me. The client was worried about eight small lumps located along the dog’s underside. Could they be flea bites? Some sort of rash? A strange form of juvenile cancer?

She was surprised to learn that the lumps in question were the dog’s nipples.

She asked why a male would have nipples. Before the advent of modern embryology, that question triggered an existential dilemma for many people. But these days the answer is known.

I started off with, “for the same reason that men have nipples.” That seemed to satisfy her, and she declined to listen to the rest of my explanation. It’s probably for the best, since the explanation is quite boring: the cells that develop into nipples differentiate prior to the release of sex hormones that lead to sexual dimorphism.