There were other, equally unverifiable tales of our ancestry: the grandfather who supposedly died, post-prandially, after falling down a manhole outside the Sydney Bridge Club; the hard-hunting 19th-century Irish aunts who rode their horses up the stairs; the Macintyre clansman who severed his own hand and hurled it to the shore in order to win a swimming race; mad Aunt Rachel who turned out, post-mortem, to be an uncle.

I have no idea whether these stories of my forebears are even remotely true. The reality was probably much more prosaic: hairy Scots-Australian sheep farmers on one side, English sailors and a smattering of vicars on the other. But I have always clung to the family legends of self-amputating aquatic Scotsmen and peculiar Wodehousian aunts.

Today, thanks to the internet and DNA testing, I could find out my origins for sure, as millions of others have already done. The tracing of family history is the world’s fastest-growing hobby, no longer restricted to brassrubbing or to elderly folk with time on their hands.

No less than six British magazines are devoted to genealogy, and only pornography is more popular on the internet. When the 1901 Census was put on the web in 2002, more than one million members of the public logged on, causing the site to collapse. The website genesreunited.co.uk boasts some ten million files and ancestry.com has 275 million names on it, but the mother of all researchers is the new genealogy software Legacy Family Tree Deluxe 5.0, which provides access to an astonishing four billion names, through records of births, deaths, marriages, land ownership, military service and so on. This is not a family tree, but a vast family forest, in which every twig, leaf and tendril is recorded.

The new Genographic Project, recently launched by the National Geographic Society, will spend £21 million over the next five years tracing the roots of mankind back to the single female who lived in Africa 150,000 years ago, and is the grandmother of us all. The project, collecting DNA samples from 100,000 people, will map global migration out of Africa by studying the Y chromosome path of the male line and the mitochondrial DNA of the maternal line.

We are very close to discovering exactly where each of us came from, and to whom we are related.

But why do we want to know? No doubt our interest in past family partly reflects disillusionment with the present. In the anomic, fast-moving modern world, tracing roots is a way of fixing your place in your own personal history. As the present becomes more globalised and grey, the past seems ever safer and more glamorous. We venerate history as never before: old is the new new. For many, tracing the generations back is harmless solipsism, a form of escapist self-affirmation. Every society in the world worships its ancestors to a degree, and there is something quasi-religious in the way that the modern DIY genealogist sifts through the archives for his ancestral bones.

The craze for family genealogy has democratised history in a way that was impossible a generation ago. The ordinary, everyday lives of your ancestors and mine hold as much fascination as the actions of the great and good, the famous and the infamous. This reflects the wider shift towards personalised microhistory: the simple men who fought the battles and not just the great men who ordered them; the women who sewed the clothes rather than the duchess who wore them. These people traditionally fell outside official history, acknowledged only as faceless cannon fodder or social statistics.

By searching out our lost ancestors, and their quotidian existences, we are looking for a part of ourselves, a reaffirmation of tribal identity: here is an extended family, but safely dead, and far less demanding and unpredictable than the real thing.

Sometimes, the discovery of an ancestor appears to confirm latter-day character traits: it is somehow unsurprising, for example, to find out that George W. Bush is a direct descendant of Richard De Clere, better known as “Strongbow”, the bloodthirsty warlord who led the Norman invasion of Ireland in the 12th century.

Family genealogy can be addictive, and expensive. James LeVoy Sorenson, the American catheter billionaire, so enjoyed discovering his Scandinavian origins that he decided to draw up the entire genetic map of Norway, at an estimated personal cost of $500 million.

The British Society of Genealogists has also cautioned that amateurs who shake their own family trees should be prepared in case something nasty or unexpected falls out: illegitimacy, bigamy, criminality or bloodlines heading in unlikely directions. The BBC’s popular genealogy programme Who Do You Think You Are? showed the actress Amanda Redman in tears after she discovered her uncle was born out of wedlock. Conversely, according to the website 1837online.com, more than one in ten of all amateur genealogists go in search of a black sheep, the family skeleton to spice up the genetic past.

Alex Haley’s book Roots told the story of the descendants of an African slave, Kunta Kinte, and set the template for family microhistory. Haley once wrote: “In all of us there is a hunger, marrow-deep, to know our heritage — to know who we are and where we have come from. Without this enriching knowledge, there is a hollow yearning . . . and the most disquieting loneliness.”

In earlier ages that hunger was fed by oral history, family legend, tribal myth and memory; today that loneliness is salved by the internet. But the effect is the same, to propel us back into the company of those who made us. Like all history, family genealogy is an act of imagination, and a matter of selection.

I, for one, will not be submitting my DNA to a genealogy database. For there are some things about the ancestral past one would rather leave ambiguous, and some legends best left undisturbed. And I know my cousin Prince Charles feels the same.

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