One possibility, of course, would be digging up Franklin's bones, which have been buried for 212 years near Independence Hall. Since that seems unlikely, L. David Roper is focusing instead on men with well-documented ties to the statesman and inventor.
Roper says all he needs from the candidates is a simple, $150 analyses of their Y chromosomes - genetic material handed down from fathers to sons.
Y chromosomes change infrequently from generation to generation. Even after two centuries, males related to Franklin would have nearly identical ones, Roper said.
"This is as close as we can get to Benjamin's DNA without exhuming him or finding one of his teeth," said Roper, a retired Virginia Tech physics professor who lives in Blacksburg, Va.
Roper said he doesn't know of any practical use for his research, though it could smash or support a bit of family mythology. His mother is a Franklin and he plans to test himself.
In the decades after his death, rumors flew that Franklin, a printer and philosopher who persuaded France to enter the Revolutionary War and helped craft the Constitution, may have fathered several children out of wedlock.
"I got a call from a guy who thinks he is descended from an illegitimate son of Benjamin's," Roper said. "Who knows? Maybe it's true. This would tell us."
A similar DNA test showed Thomas Jefferson was related to the child of one of his slaves, Sally Hemings. Donors would have to pay the $150 fee, which would go to the lab for the testing.
DNA sampling is painless, requiring only a few cells swabbed from inside of the cheek, but it does have limitations, said Dr. Scott Woodward, a Brigham Young University professor and expert on molecular genealogy.
Y chromosomes can tell only whether someone is related to another person, not whether they are directly descended from them, he said. The tests also don't work for women, who have no Y chromosome and whose X chromosomes change more frequently from generation to generation.
Roper has already received DNA samples from several possible Franklin relatives, most of whom share a similar pattern of Y chromosome markers. He is still working on estimating the most likely sequence for the founding father himself.
In the meantime, Roper said he'll also continue looking for something that might have Franklin's actual DNA in it - like a tooth that might have been pulled by a dentist, then hidden away.
"We were thinking about placing an advertisement in a dental journal, trying to see if someone held on to a souvenir, centuries ago," he said.
By David B. Caruso By David B. Caruso