Commercial DNA tests that claim to tell people whether they are related to Richard III or descended from the Vikings are no more than "genetic astrology", scientists have warned.
Customers are being charged up to £300 to learn whether they have links to famous people or societies despite the fact many of the tests are not backed up by scientific evidence, experts said.
The amount of DNA any individual inherits from relatives just a few steps up their family tree is negligible compared with the vast amount we all share from common ancestors.
It means any ancestral "history" identified by a simple genetic test is just one of dozens of possible interpretations, and to try to trace our lineage directly through our genes is "absurd", they claimed.
Private genetic tests have become big business in recent years, with many companies offering tests which claim to identify whether people are related to famous figures such as Napoleon or Cleopatra, or have DNA from specific racial groups.
Last year the website ancestry.com was valued at $1.6 billion (£1 billion) and at least 40 companies offer genetic ancestry tests around the world for prices between £30 and £300.
At the recent Who Do You Think You Are? Live roadshow in London, customers were offered a range of DNA tests claiming to determine whether they were related to Richard III or descended from Roman soldiers.
A warning about the accuracy of the tests was made by the Sense About Science campaign group, which said "such histories are either so general as to be personally meaningless or they are just speculation from thin evidence."
The warning was backed by a number of leading genetics experts. Steve Jones, Emeritus Professor of Human Genetics at UCL said: “On a long trudge through history – two parents, four great-grandparents, and so on – very soon everyone runs out of ancestors and has to share them.
"As a result, almost every Briton is a descendant of Viking hordes, Roman legions, African migrants, Indian Brahmins, or anyone else they fancy.”
His colleague Prof Mark Thomas said: "These claims are usually planted by the companies that provide these so-called tests and are not backed up by published scientific research. This is business, and the business is genetic astrology.”
Tracey Brown, Director of Sense About Science added: “Genetics researchers are telling us that you are better off digging around in your loft than doing a DNA ancestry test if you want to find out about your family tree."
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