When I was a kid, my mom told me a story about her grandfather: That he got in trouble with some white men down south, and escaped lynching by running to Chicago. That he chose his new last name "Jones," because it was the most common name in the phone book. That, for years, he would sit in his chair facing the door, shotgun on his lap, waiting for them to come for him.I used to dream about this image — nightmares, really.Thing is, I never knew much more about the story than that — until last month, when I found out the secret was literally in my blood the whole time.See, I took one of those DNA tests a while back, and the company connected me to a bunch of people listed as "cousins." Now, most of these people were just randos — I mean we're all cousins if you go back far enough. But one woman, Donna, reached out to me, because it turned out not only did we have genetic ties together, but also several of her family members and my family members reported DNA matches. But we couldn't figure out why.That was two years ago. And then, a month back, Donna contacted me again. She had figured out the reason why our ancestral surnames didn't match up: Our common relation was my great-grandfather, the one person in my family who had changed his name.From the historical records she found, this is the best I can put the story together:In 1904, my family — black farmers in Aiken County, S.C., — bought a mule. At this time and place, a mule was more than just an animal, it was a means to a livelihood. The problem was, the guy who ran the country store claimed the mule was actually his. He said it was sold illegally by someone leasing it and now he wanted it back.My cousin had already paid his money, so he told the merchant no. He said that the issue was between the merchant and the leaser. But my cousin was black and poor, and the merchant was white and wealthy, and it was 1904 in the south. So it didn't end well.The merchant and his hired hand showed up at my ancestor's home on Christmas Eve, past 11 at night. They illegally came in the house, pulled a gun on my cousin, bound his wrists behind his back. They were planning on pulling him out, in the dark, to deliver what they considered justice — which likely meant hanging him until his neck snapped.All this over a mule.But the thing is, they didn't check the rest of the house. They didn't realize my great-grandfather was in a room just beyond, with a shotgun aimed right at them. He was 11 years old.When he fired, he hit the merchant first in the shoulder, and then in the gut. Shot and in shock, the guy walked around the room before finally collapsing and dying soon after.My great-grandfather got away — partly because the resulting lynch mob wasted time chasing false leads, partly because his older brother whisked him away to Chicago, where the Great Migration of northbound southern blacks covered their tracks for them.And that's what makes this story so rare. Because between 1877 to 1950 more than 4,000 black people didn't escape. Instead, they were publicly murdered — supposedly for crimes, but always to reinforce the social order that was white supremacy.The horror of lynchings has always been a part of my ancestral memory; I'd imagine that's true for a majority of African-Americans. I even wrote a graphic novel about lynching, so it's not a new subject to me.But knowing the real story of my own family's brush with lynching? It made it real. Reading the newspaper clippings, seeing the pictures, feeling the utter vulnerability of black life in tin-roof shacks, the darkness of the fields and the hostile world beyond them. Knowing how much has changed since then; knowing how much hasn't.I get now why my great-grandfather sat at the door with his shotgun. It wasn't about defense; it was about PTSD.I was on the road when I found out the whole story, so I called my daughter to break the news, knowing she probably wouldn't care because for her, at 16, it's beyond imagination. I was trying to get her to understand the enormity and figured I was failing.But then she said: "Wait, Dad, if they lynched your great-grandfather, you wouldn't be here."No baby, I wouldn't be here. And neither would you. Or your brother or your sister. Or grandmother, or aunt and cousins. None of us would be here.When I hung up the phone, here's the part that hit me: More than 4,000 people murdered. Erased. Family trees pulled at their roots.So tell me this, America: How many other people aren't here? Copyright 2018 Fresh Air. To see more, visit Fresh Air.