23andMe.com, a California-based genetic testing company, spruiks ancestry testing on its website. For US$99, you can discover the composition of your ancestors, your genetic relatives, your maternal and paternal lineages, and the percentage of your DNA which comes from Neanderthals. "Trace Your Family Lineages Back 10,000 Years and Beyond," it says. "Find out if you share an ancestor with famous figures such as Marie Antoinette and Thomas Jefferson."
Similar companies around the world are springing up - to the enrichment of some geneticists and the dismay of others.
Five years ago three US scientists writing in the New England Journal of Medicine, described ancestry tests as "premature attempts at popularising genetic testing". One called the tests "recreational genomics".
Just as huffy was a British geneticist, Mark Thomas, of University College London, who wrote in the Guardian this week that, "The truth is that there is usually little scientific substance to most of [these claims] and they are better thought of as genetic astrology". A closer study of ancestry claims shows that they are very easy to make. "It has been reasonably estimated that around 5,000 years ago everybody who was alive was either the common ancestor of everybody alive today, or of nobody alive today; at this point in history we all share exactly the same set of ancestors," says Dr Thomas.
"'Genetic Astrology' stories are often promoted by people with financial interests in genetic ancestry testing companies… Perhaps it is harmless fun to speculate beyond the facts, armed with exciting new DNA technologies? Not really. It costs unwitting customers of the genetic ancestry industry a substantial amount of hard-earned cash, and it disillusions them about science and scientists when they learn the truth, which is almost always disappointing relative to the story they were told."