"If I want to go look up my French-Canadian ancestors there's almost nothing to help me more than two or three generations back," Eastman said. "It's not going to be as rosy an experience as some of the online services would like you to think."

Herbert Huebscher, a retired electrical engineer from Franklin Square, N.Y., found himself in that kind of situation when he went looking for his ancestors. The most distant ones he could identify were Ukrainian Jews who were living in a small village near the Romanian border around 1830.

"In general, Jewish paper trail genealogy tends to hit a brick wall around 1800, give or take 50 years," Huebscher said.

To push farther into the past, he turned to DNA.

DNA testing has made it possible for people to make connections when the paper trail fades into tatters. The technology was used several years ago to show that Thomas Jefferson — or one of his male relatives — fathered a child by his slave Sally Hemings. It has also shown that a significant proportion of men in modern Ireland can trace a direct male descent from Niall of the Nine Hostages, a legendary 5th-century king.

Customers of Relative Genetics, a company based in Salt Lake City, have traced their roots to Scotland, Africa and other distant countries with DNA testing.

Huebscher had his own genetic profile tested by a Houston-based company called Family Tree DNA. He found that he matched one other individual in the company's database, a South African-born Londoner named Saul Isseroff.

It turned out the two had some very distinctive anomalies in their DNA profiles, which allowed them to identify other matches as new Family Tree DNA customers joined the company's database. They have now found more than 40 closely matched families. Nearly all of the families were Jewish, and nearly all of them trace their heritage back to Eastern Europe — though oddly enough, one family traces its roots to Puerto Rico.

A statistical analysis of the genetic data showed that whether they were named Huebscher or Isseroff, Wolinsky or Rosa, all of the families must have shared a single common ancestor who probably lived four or five centuries ago, long before most Jews even had surnames, much less written vital records.

Though his research is not yet conclusive, Huebscher believes the common genetic ancestor may have been descended from Sephardic Jews who lived in Spain before the Inquisition.

Just a little patience may be enough to solve the mystery, said Peggy Hayes of Relative Genetics.

"The databases are growing very rapidly," she said. "As the genetic genealogy databases grow, the success rate is going to grow as well."

For some lucky people, the techniques of extreme genealogy make it possible to trace their origins back not just centuries, but a millennium or more. All they have to do is link themselves to a royal line, Drew explained, and ride it back as far as it goes.

"We're all related to royalty," Drew said.

The trick is to prove it. But thanks to the power of extreme genealogy, it can be a lot easier than you might think.

Every French monarch since the 10th century was a descendant of Charlemagne. So was William the Conqueror, which means every British monarch since 1066 also descends from the King of the Franks.

And that means at least 18 U.S. presidents, 14 first ladies, Walt Disney, Colin Powell, Brooke Shields — a good number of the people whose family history has ever been seriously researched by genealogists — can trace their ancestry to Charlemagne.