It is not often that a shady old joke partakes of prophecy. Such is the tale of two swains and the girl whose favors they enjoyed in equal measure. On learning that the girl became pregnant, the two gallants, not being sure of who the father was, agreed to equal partnership in supporting the expected child. On the day of delivery, however, a surprising telegram arrived from one of the partners to the other, who happened to be out of town. The message read: "Toots gave birth to twins. Mine died."
This joke will provoke little laughter now after we have read the report by Terasaki et al1 on twins with two different fathers identified by HLA typing. In fact, some of the punch had gone out of the joke much earlier when Archer2 reported in 1810 the birth of twins, one of whom was white, the other