fraternal twins to have different fathers // canavarlar

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. --Nancy Ann N., Chicago

Cecil replies:

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.

--CECIL ADAMS

Heteropaternal Superfecundation
http://www.people.virginia.edu/~rjh9u/twindad2.html