Medicine: Double Blood

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When Mrs. McK., 25, gave a pint of blood for Britain's National Blood Transfusion Service in Sheffield last March, the doctor and nurses who checked her saw nothing unusual. But when technicians typed the blood, they did a double take, and with good reason: Mrs. McK. was the first human being in medical history with a double set of blood groups. Her red cells were 61% type 0 and 39% type A.

Puzzled, the researchers asked Mrs. McK. whether she was a twin. No less puzzled by their apparent second sight, Mrs. McK. replied that she had had a twin brother, who died when three months old. That explained it, they figured: in the womb there had been a connection between the arteries of the fraternal twins, and Mrs. McK. had picked up some of her brother's blood-making cells.

In cattle, a female twinborn with a male is a freemartin, intersexed and usually sterile. Said the British Medical Journal: Mrs. McK. has had a child and is clearly feminine—no human freemartin.