Millions of people in recent years have sent off samples of their saliva to DNA-testing companies like 23andMe and Ancestry.com hoping to find out where their forebears came from and whether they have mystery relatives in some distant land, or even around the corner.

The trend itself can be traced to an Italian physician and geneticist, Luigi Luca Cavalli-Sforza, who died on Aug. 31 at his home in Belluno, Italy, at 96. He laid the foundation for such testing, having honed his skills more than 60 years ago using blood types and 300 years of church records to study heredity in the villagers of his own country.

Dr. Cavalli-Sforza was a pioneer in using genetic information to help trace human evolution, history and patterns of migration. The founder of a field that he called genetic geography, he was renowned for synthesizing information from diverse disciplines — genetics, archaeology, linguistics, anthropology and statistics — to explain how human populations fanned out over the earth from their original home in Africa.

David Reich, a professor of genetics at Harvard Medical School, said in an interview that Dr. Cavalli-Sforza was the first scientist to predict that there would be “enough information in genes to determine where people came from in the world and who they’re most closely related to.”