LOS ANGELES (AP) — If there's a bigger cheerleader for genealogy research than Henry Louis Gates Jr. it's unlikely they're nearly as well-connected.

The prominent Harvard professor once again lures the famous and celebrated to PBS' "Finding Your Roots," which shares their ancestry and family stories as uncovered by impressive research and science.

In the fourth season beginning Tuesday (check local listings for time), the three dozen subjects include Scarlett Johansson, Lupita Nyong'o, Sean Combs, Amy Schumer, Garrison Keillor, Aziz Ansari, filmmaker Ava DuVernay, author Ta-Nehisi Coates and Christopher Walken.

Larry David, whom Gates said he'd "bugged" for three years to go under the "Roots" microscope, finally agreed and discovered that he's related to Bernie Sanders, whom David memorably impersonated on "Saturday Night Live." Their separate family stories are on the season opener.

David said he was reluctant to have personal details disclosed on TV but was glad he finally took part, lauding the "incredible job" done by researchers.

There were other revelations that took him aback, he said. David learned of ancestors who settled in Birmingham, Alabama, in the 1840s, owned two slaves and fought for the Confederacy in the Civil War. A hundred years later, many aunts, uncles and cousins on the maternal side of his family died in Nazi Germany's Holocaust.

But "Finding Your Roots" is aimed at more than satisfying individual curiosity and telling an engrossing story, said Gates, an executive producer and writer as well as host of the series: It carries a message of shared origins that he argues can benefit society.

The science of DNA proves that "there aren't four or five biologically distinct races. We're all from one race, the human race, genetically," Gates said. "And we know that genetically we all ... descended from common ancestors that left the African continent 50,000 years ago. That's a fact."

Detailing how different ethnic groups contributed to world history and how their experiences "merged or conflicted" with those of other groups is also of immense value, he said.

"It's part of a larger education process to make us all realize we're fully human," Gates said.

Advances in DNA testing and the increased digitization of records benefited those who participated this year, he said, while some searches required plain old shoe leather as well.

Among the stars with standout stories:

— Carly Simon, who was eager to find out whether her maternal grandmother, who came to the United States from Cuba, had her lineage right: She claimed to be the offspring of the king of Spain and a Moroccan slave.

Researchers traveled to Cuba to search out Catholic church records unavailable online and found "an amazing family tree," Gates said, one different than expected. Simon's grandmother was found to be 40 percent black, making the singer-songwriter 10 percent black.

Her grandmother "invented this crazy story, this fabrication, because she knew she was from a mixed-race heritage, and that was very unpopular in the 1950s and '60s," Gates said.

— Tea Leoni, who asked the show to focus on finding the family of her mother, Emily Patterson, an adoptee who never knew the names of her biological parents.

Over a period of months, Patterson's DNA was run through databases that hold DNA results for some 6 million people, Gates said. A match would show they had a common ancestor.

The candidates were narrowed to a pair of sisters, one of whom proved to be Patterson's mother and who, at 96, was still alive, Gates said. A private meeting was arranged with her for Leoni, Patterson and Leoni's daughter.

Research also revealed Leoni's biological mother's father, and traced his family back to her seventh great-grandfather, born around 1690, and his Virginia-born son who at one point lived near George Washington.

— Questlove, the musician, producer and writer born Ahmir Khalib Thompson, found his family has an extraordinary place in U.S. history.

In 1860, five decades after the slave trade to the United States was abolished, a ship commissioned by a Southern planter illegally brought about 110 slaves to Mobile Bay, Alabama, from a port now located in the Republic of Benin, Gates recounted.

It was the last known slave ship to arrive in the United States, Gates said. Aboard was a couple who would take the names Charlie and Maggie Lewis and who were recorded on the 1880 census as African-born.

As freed people, they settled in an Alabama town largely made up of others on the ship, and Questlove's distant cousins who live in the area shared with him a photo of Charlie Lewis, Gates said.

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Lynn Elber can be reached at lelber@ap.org and on Twitter at http://twitter.com/lynnelber.