In the previous installment of Hammwatch, I wrote that nobody seems to know if Olympic all-around champion Paul Hamm and his twin brother, fellow Olympic gymnast Morgan Hamm, are identical or fraternal twins. The Washington Post says identical. The AP says fraternal. The U.S. Olympic Committee says identical. USA Gymnastics says fraternal. Are the twins playing an elaborate prank on the nation's media? Did Paul and Morgan think they were fraternal (or identical), but then find out later in life that they were identical (or fraternal)? Are they, as many readers suggested, really "half-identical" twins?
Five-Ring Circus reached Paul and Morgan's father, Sandy Hamm, in Athens today. So, Mr. Hamm, are your sons identical or fraternal?
"Their parents do not believe that they're identical," he says.
Mr. Hamm then lists the brothers' physical differences: The circle of hair on the top of each boy's head goes in opposite directions, their teeth are different, their noses are different.
But these are just the observations of a parent who has spent more than 20 years staring at his children. Have they taken a DNA test to confirm that they are fraternal?
"We've never had them genetically tested," Mr. Hamm reports.
Have the twins ever expressed interest in getting such a DNA test? "Nope."
Does he get annoyed when newspapers say that the twins are identical (or fraternal)? "No, no. We don't care at all. It's immaterial."
"I would call them fraternal, but twins are a weird thing," he continues. "Some people say that there's [such a thing as] half-identical. They came out in separate sacs with a shared placenta, so it's murky."
Separate sacs with a shared placenta—that means the Hamms are diamniotic, monochorionic (DiMo) twins. According to Dr. Kurt Benirschke, an expert in the field of placental pathology, the answer to this mystery isn't murky. The "overwhelming" number of DiMo twins are identical. Asked if he could give a percentage of DiMo twins that are identical, Dr. Benirschke says, "99.999 percent."
The parents say fraternal. Paul and Morgan themselves say, according to AP reporter Nancy Armour and USA Gymnastics spokesman Brian Eaton, that they are fraternal. But medical science says identical. Slatesides with science, and hereby declares that American gymnasts Paul and Morgan Hamm are identical twins.
Addendum, Aug. 19: Dr. Adam M. Dubin, an anatomic and clinical pathologist at Hinsdale Hospital in Hinsdale, Ill., writes in that it's possible that what the Hamms' father identified as a "shared placenta" could have been a "fused placenta"—that is, two placentas fused together that have the appearance of a single mass. If the placenta was fused, then it's possible the Hamms are diamniotic, dichorionic (DiDi) twins, and they might be fraternal. But if there was in fact just a single placenta, then the Hamms are diamniotic, monochorionic (DiMo) twins, and they are certainly identical.