London - Go back far enough in your family tree and there may be a surprise in store.
One in 100 people who delve into their ancestry should expect to find a child who was the product of adultery in western Europe.
It appears this was most likely to happen in cities, where married women were more likely to meet men they could have affairs with. The greater anonymity meant the risk of scandal was reduced.
University scientists from KU Leuven in Belgium investigated the likelihood of a baby being born to a man other than the mother’s husband from 1375 to the present day in western Europe.
They took DNA swabs from 513 pairs of men from Belgium and the Netherlands whose families were related at least three generations earlier, and looked at genealogical data for more than 6 800 of their ancestors going back more than 600 years.
If the male line had gone unbroken, the Y chromosome would have been the same in every pair – but for 96 of them it was not.
They found around one percent of people had someone in their family tree whose biological father was not the one named on the birth certificate.
But the rate of babies born from adultery rose to almost six percent among the urban working class, with farmers’ wives in under-populated villages least likely to have a child out of wedlock.
The classes with a lower rate of babies born through infidelity included craftsmen and merchants.