Tracing our ancient ancestors is a tall order, but DNA research companies are now leading the way. Shane Hegarty puts one to the test

I rub a slither of card against the inside of my cheek and post it to an address in Oxford. A few weeks later, an envelope arrives containing a certificate telling me that my DNA shows my maternal line can be traced back 20,000 years to western Europe. I belong, it tells me, to the clan of Helena - one of "seven daughters of Eve" from which all modern Europeans are descended. Helena's offspring is the most widespread of them. I am, in a word, common.

The test was run by Oxford Ancestors, a leading company in a new trend in genealogy. It promises to trace family trees right to the root. It won't tell you about your great-great-grandmother, but it will attempt to pinpoint where the woman who began your family came from.

The company was set up by Prof Bryan Sykes, the first scientist to extract DNA from old bones. Among his high-profile cases was Oetzi, a 5,000-year-old ice body found in the Tyrol, Austria. Prof Sykes used Oetzi's DNA to track a living descendant - a female management consultant from Bournemouth. His research led him to conclude that 95 per cent of modern Europeans are descended from just seven women - the "seven daughters of Eve" - who survived in Europe or the near East during the Ice Age.

They are not the only women to have lived then, of course, but are those who survived long enough, and had enough daughters, for their DNA to proliferate. In all, Prof Sykes has identified 36 global clan mothers, although the occasional person still turns up with DNA that cannot be linked with any of these.

Set up in 2001, Oxford Ancestors now handles 5,000 inquiries a year, with about 20,000 people having used the service. In the US, companies such as Family Tree DNA and Ancestry by DNA are similarly popular. The DNA searches occasionally have a more serious aim than mere curiosity. Because of their slave roots, some African-Americans have used DNA testing to identify a possible homeland. There have also been efforts by people to prove they are descended from certain Native American tribes so that they can claim a share of profits from casinos on tribal lands.

However, despite its popularity, DNA genealogy has its critics, who point out that it often tells people what they could have guessed already. The British Human Genetics Commission looked into the industry and concluded that "there was a feeling that the scientific information that genealogy tests could provide might not be as precise as some of the companies may be suggesting and this was an area in which people should be aware of the reality of what they are being offered".

The maternal line is traced through the chain of mitochondrial DNA, which is passed from mother to children. However, many geneticists have pointed out that it forms only a part of a person's genetic make-up, or as one has written, it "represents just a single twig from an extremely bushy family tree". In looking at the DNA that has been passed on from your mother's mother's mother, it rules out all the other great-great-grandmothers who have contributed their DNA.

What's more, while we might like the idea of belonging to a particular clan, if we go back far enough we're all related to one another anyway. Mathematically, a person has only to trace back 15 generations to be directly related to half a million people. It suggests that we are all family.

However, that is not to dismiss DNA genealogy altogether. Research at Trinity College, Dublin identified the male Y-chromosomal signature of the clan of Niall of the Nine Hostages, the High King at Tara from 379 to 405.

Oxford Ancestors offers the opportunity for people to see if they are connected to this Uí Neill clan, although it is a men-only (given that women don't carry the Y-chromosome) genetic marker which hardly changes at it is passed down the paternal line.

"The Y-chromosome has a more definite structure. It's not as diffuse and can sometimes be more securely identified with historical families. There is more definition between regions," explains Dr Dan Bradley, of TCD's Smurfit Institute of Genetics. "There is a lot of potential for it, if for example people are seeking out their Irish roots. They might have an Irish surname, but we might know from their Y-chromosome if they are from north, east or west. But it will always be a probability rather than a certainty."

By the way, he tells me, the Hegarties are descended from the Uí Neill clan. It's an exclusive club: just me and about three million other men.

www.oxfordancestors.com, 0044-1865-374-425