February 13, 2009

Not as much infidelity as once thought

British researchers suggest the often quoted 1 in 10 figure for children born through infidelity is unlikely to be true.

Dr. Turi King and Mark Jobling from the University of Leicester examined the Y chromosomes of more than 1,600 unrelated men with 40 surnames -- including variations in spelling. Sons inherit both the Y chromosome and generally the surname from their fathers, unlike daughters.

The study, published in the journal Molecular Biology and Evolution, found men with rare surnames such as Grewcock, Wadsworth, Ketley and Ravenscroft tended to share Y chromosomes that were very similar, suggesting a common ancestor within the past 700 years.

However, men with common surnames, such as Smith, were no more likely to have such a common ancestor than men chosen at random from the general population.

People with a rare surname are very likely to be related, as the surname is likely to have been adopted by only one or two men initially, so anyone now sharing this surname but with a different Y chromosome to the majority is likely to have an ancestor born illegitimately.

People often quote a figure of 1 in 10 for the number of people born illegitimately, Jobling said in a statement. Our study shows that this is likely to be an exaggeration. The real figure is more likely to be less that 1 in 25.