A genetic study of British men finds a one in four chance that two strangers with the same last name share an ancestor. The relationship implies that certain surnames have a unique DNA signature--a fact that could help police narrow down suspects in some unsolved cases. But the criminally intent John Smiths of the world need not worry, because the signatures are found predominantly for rare surnames.
In Britain, surnames came into wide use around 1300 C.E., with several common names chosen because of occupation or location. For example, many blacksmiths in England took the name Smith, so the 560,000 Smiths now in the United Kingdom are largely unrelated. On the other hand, some names, such as Sykes, have been traced back to one man or a small handful of men. But even in these cases, the genetic lineage can be blurred by illegitimacy, adoption, and name changes.
Geneticist Mark Jobling of the University of Leicester and his colleagues wanted to find out how many family names have a genetic underpinning. They first recruited 150 men with different names of English, Scottish, and Welsh origin and then paired each of them randomly with a man of the same surname from the electoral registers. When the researchers compared 17 genetic markers on the two matched men's Y chromosomes (For more about the method, see ScienceNOW, 21 December 2005), they discovered 16 of the pairs had identical markers. Allowing for small mutations, the scientists calculate that up to 24% of the matched pairs share a forefather within the last 700 years, as reported 21 February in Current Biology. The percentage rose to 50% for surnames held by less than 5000 individuals.
Forensic investigations could theoretically use this Y-to-surname linkage to match an unknown DNA sample to a specific last name--especially for less common names, says Jobling. With a Y chromosomes database of 39,000 rare names, the authors estimate a matching rate of about 14%, which would correspond to roughly 10 murder and 57 rape cases each year in the U.K.
"The benefits to investigations could be substantial," says Jon Wetton, a senior researcher at the Forensic Science Service, a government-owned company providing forensic services to U.K. police. But he says a rare-names database would have to be built from scratch, since Y chromosome information is not currently kept in the criminal DNA database. There are also ethical issues about gathering DNA from innocent people who happen to have certain last names. Geneticist Peter de Knijff of the University of Leiden in the Netherlands, who also does forensic work for the Dutch police, says he does not keep surname information for his genetic research. "I don't want to be put in the situation where [the authorities] might ask for that information," he says.