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."