A Straight Dope Classic from Cecil's Storehouse of Human Knowledge

Is it possible for fraternal twins to have different fathers?

June 24, 1986

Dear Cecil:

My husband and I have an ongoing argument. I say it is possible, though highly unlikely, for fraternal twins to have different fathers. My husband and his friends say this is nonsense. We are relying on you as the final authority in resolution of a $100 bet.

Cecil replies:

We will deal with this vital issue in a moment, Nancy, but first a word. Cecil has been settling bets for as long as he can remember. Yet despite his oft-stated willingness to accept kickbacks and graft, all he has gotten for his trouble is an inflatable Dino the Dinosaur, a bootleg Bob Dylan tape, and a pair of long johns designed for a guy who's built like Santa Claus and hung like a horse. (Don't ask.) A mighty sorry showing for 13 years of selfless service. Well, I've had enough. Since you stand to come into some serious money pretty soon (see below), I expect you to show the proper gratitude. They say Paris is beautiful this time of year. 'Nuff said.

All right, then. Not only is it possible for fraternal twins to have different fathers, it has actually happened. There's even a medical term for it: superfecundation. The classic case, which is discussed in Williams Obstetrics (1980), was recorded in 1810 by John Archer, the first doctor to receive a medical degree in the United States. According to Archer, a white woman who had sex with a black man and a white man within a short time subsequently gave birth to twins — one white, one mulatto. Other cases have been reported since.

Superfecundation is possible because fraternal twins result from two separate eggs fertilized independently. Some think it happens fairly often, but until recently it was difficult to prove, due to the crudeness of the traditional testing method, which involved comparing blood types. In 1978, however, Dr. Paul Terasaki of the UCLA School of Medicine reported in the New England Journal of Medicine that he and his colleagues had conclusively established a case of superfecundation using a sophisticated procedure called tissue or HLA (human leukocyte antigen) testing. This technique can also be applied to more conventional cases. Prospective paternity-suit litigants, take note.

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