GEOFF BENNETT: For more than two centuries, a question has hung over the legacy of Thomas Jefferson: Did the nation's third president father children with Sally Hemings, the woman he enslaved at Monticello?

Historians have long treated Jefferson's paternity of Hemings' children as established.

Now a remarkable scientific investigation is offering what researchers say is the most conclusive answer yet.

It began with a single strand of hair pressed between the pages of Jefferson's Bible at the Smithsonian.

That discovery launched a 15-year investigation involving DNA scientists, historians, genealogists, and descendants of both Jefferson and Hemings.

The story of that investigation and what it reveals is told in the new book "History by a Hair: Thomas Jefferson, Sally Hemings and Solving a 200-Year-Old Mystery."

Its author, Richard Kurin, is a distinguished scholar and ambassador at large at the Smithsonian Institution.

We're also joined by Jefferson and Hemings' descendants David Miller and Clara Lee-Nutt.

Welcome to the "News Hour."

CLARA LEE-NUTT, Descendant of Thomas Jefferson: Thank you.

RICHARD KURIN, Author: Good to be here.

GEOFF BENNETT: And, Richard, historians had largely accepted that Thomas Jefferson fathered Sally Hemings' children.

What remained unanswered for you that led you on this 15-year journey?

RICHARD KURIN: Well, there were still people who questioned it, a few historians, members of the family and so on.

And I think the idea of being able to firmly establish that was very appealing for many people.

GEOFF BENNETT: And how did this all come together?

RICHARD KURIN: Well, it was a hair in the Bible, and we discovered it while we were conserving the Bible, a national treasure, at the Smithsonian.

And I said, wait.

If that's a hair in Jefferson's Bible, maybe we can get DNA from it.

If we get DNA and we can analyze the DNA of contemporary descendants, maybe we could prove this once and for all.

GEOFF BENNETT: And, of course, 200-year-old hair doesn't strike most people as an obvious source of a of a usable genome.

How do you know that it was actually Thomas Jefferson's strand of hair?

RICHARD KURIN: Well, it actually turned out, Geoff, that the Bible hair wasn't Thomas Jefferson's, but another hair was, and that was kept in a packet at Monticello by the Thomas Jefferson Foundation.

And when we sampled that, we found that it had the Y chromosome of the Jefferson males family.

It had the mitochondrial DNA of Thomas Jefferson's mother, which we found matched a woman living in Florida, seven generations of females.

So it could only be someone -- the hair of somebody who had Thomas Jefferson as a father and Thomas Jefferson's mother.

It had to be Thomas Jefferson's.

The provenance was also great.

This was a hair, and I don't make this up, that was clipped from Thomas Jefferson's head on July 4, 1826, the day he died.

And we had historical provenance to show that.

GEOFF BENNETT: And, Clara, in many ways, you didn't need the DNA to know who you were.

You grew up knowing that you were a descendant of Jefferson and Hemings.

Still, what did it feel like to have this confirmed by DNA evidence?

CLARA LEE-NUTT: Well, to me, it was more about my father being validated than being tied to Jefferson.

I lost my father when I was 10.

Some of my very precious memories of him are speaking about Jefferson, hearing him talking about Jefferson with his siblings, and then losing him at the age of 10 and having not asked enough questions.

So this was a fulfillment of so many -- I met so many people who could answer some of the questions for me.

I have met cousins who knew my father, and it's just been wonderful.

It's just been a wonderful moment.

GEOFF BENNETT: When you were 12, as I understand it, you visited Monticello.

CLARA LEE-NUTT: Oh, yes.

GEOFF BENNETT: And you asked, "Tell me where Sally Hemings slept."

And what was the response that you got?

CLARA LEE-NUTT: Oh, my goodness.

Well, and the thing is, I had prepared for this trip.

My father had passed two years prior to my trip.

And, in my mind, I'm like, oh, my gosh, I'm going to go to this place that my father spoke of, and they're going to know me.

I'm going to go in there and I will -- there will be something familiar, something that I can hold on to.

And I was naive.

So I go through there.

And, of course, I'm dressed for the occasion.

I have on my polyester bell bottoms.

I have my Afro puffs, my halter.

What could possibly go wrong?

So I'm walking through.

And I -- they weren't mentioning Sally at all.

And I finally said: "Well, where did Sally Hemings sleep?"

And the tour guide turned and just said: "There is no reason to believe that woman" -- she wouldn't even say Sally's name -- "that that woman ever set foot in this house."

And there was a collective groan from my classmates, and it just -- it was like she put nails in my father's coffin that day.

GEOFF BENNETT: David, you have said that you already had believed that Jefferson fathered Sally Hemings' children.

So what do these results mean to you?

DAVID MILLER, Descendant of Thomas Jefferson: Geoff, to me, it's very important that we are a family and that we can now acknowledge and accept the entire family, that that's what really it boils down to for me.

And the bonds I have made just this weekend and prior with Clara and some of the other cousins has just been a wonderful experience.

GEOFF BENNETT: You refer to them as cousins?

DAVID MILLER: Oh, yes.

GEOFF BENNETT: Yes.

It's interesting, because this history is so often told as two separate branches of the Jefferson family.

But to hear you describe it as one and the same is striking.

DAVID MILLER: Yes, and I'm speaking just for myself, to be clear.

But there are many in the -- I call it his first family, if you will, just like a first wife, second wife thing, many that feel the same way.

There are many that don't feel that way.

So... GEOFF BENNETT: David, for those family members who don't accept this evidence and don't accept this history, what do you think their responsibility is?

DAVID MILLER: I think their responsibility is to face up to science, number one.

You can argue lore, you can argue what somebody else says may or may not be correct, but science is science.

And when you accept that, it leads pretty much down one path.

GEOFF BENNETT: What does this discovery, this confirmation?

What does it mean for our overall understanding of Thomas Jefferson, who he was, and his involvement in the practice of slavery?

RICHARD KURIN: Well, look, Thomas Jefferson wrote the most famous phrase probably in American history, all men are created equal, they're entitled to these rights, and that's become a national mission statement.

But we fell short of that even from our founding.

And I think our national quest is the perfection of that aspiration.

It's complicated.

And, look, we had a civil war over slavery; 700,000 people died.

And I think the lesson for me in all of this has been not to disparage people or whatever, but recognize our country has a complicated history.

We have overcome a lot of challenges.

We still have some things to face, but, altogether, we're one American family.

The issue of Jefferson's progeny, whether through his wife, Martha Wayles, or through Sally Hemings, they're all Americans.

They're part of one American family.

We're a complicated family, and we share a future together.

So we better figure out how to reconcile those differences.

GEOFF BENNETT: Clara Lee-Nutt, David Miller, Richard Kurin.

The book is "History by a Hair: Thomas Jefferson, Sally Hemings and Solving a 200-Year-Old Mystery."

Thank you all.

RICHARD KURIN: Thank you, Geoff.

CLARA LEE-NUTT: Thanks for having us.