Percent Poe

The family lore, through my DNA dad’s family, is that we’re descended from Edgar Allan Poe. If you don’t like my shameless name-dropping, then just stop here and read a different story instead. Unless you like tedious math—then just roll your eyes and carry on.

For those of you who didn’t go to high school in the US, or prefer not to remember those days: Edgar Allan Poe was a famous American author from the first half of the nineteenth century, best known for well-crafted, psychologically disturbing poetry and short stories, though he also was a well-regarded literary critic and wrote a novel or two. In my teenage years I devoured his short stories. Mostly at bedtime. Slept just fine, thank you.

My DNA dad was vague about exactly how we’re related to EAP, but for sure his mother was a Poe. One of my cousins on that side of the family took the first name Poe, which I think is a wonderfully provocative name. Rhymes with Boe, don’t you know.

EAP had no children, and neither did his siblings. At most Max and I are descended from one of his first cousins. At most, but maybe not at best.

Apart from his literary genius, EAP doesn't really provide the kind of legacy that makes you want to brag about your connection to him. He married his thirteen-year-old first cousin. He was plagued by addiction. He also had a terrible childhood—his mom died very young and his dad handed him off to a friend to raise. Trauma like that can be transmitted through generations, through a process I recently learned about from Beau called epigenetics. Has something to do with how the little double helices continue to squirm with discomfort, even after they’re passed on to your children, grandchildren, great-grands and so forth. Tenacious little bugger, trauma.

So let’s calculate exactly how much of my DNA is squirming with EAP literary genius and nineteenth-century psychosis. For this calculation I am relying on a technique I learned in a course in population genetics that I took in college, a mere four decades ago. I remember it well.

The population genetics course was taught in the anthropology department, and I signed up for it to trick the administration into thinking I was fulfilling a social science distribution requirement, when really it was a science course. My deception totally worked. And also, I loved the course.

That’s what liberal arts education is about, folks. It’s making a physics major take courses in other areas, where they might reluctantly stumble upon gems. Interests they didn’t know they had. I also took a creative writing seminar from Wallace Stegner. Twelve of us with one of the greatest living American authors (alas, no longer with us). A physics major got to do that.

The downside of getting a Bachelor of Arts (Arts!) in physics meant that I didn’t learn all that much physics or math. I learned quantum mechanics from a three-volume set called The Feynmann Lectures. A wonderful read, masterfully written and funny in places. I still have a copy if you want to borrow it. But it’s mostly prose, not math.

When I got to graduate school, my academic advisor looked at the courses I’d taken as an undergrad, tented his fluffy white eyebrows and said, hmm. You haven’t even taken partial differential equations? I shook my head no. He looked at my transcript again. And you learned quantum mechanics from The Feynmann Lectures?

He was disappointed in the admissions committee. Another one of those liberal arts students, he no doubt was thinking. I didn't mention getting to take a seminar from Wallace Stegner.

So I spent my first year in remedial math, and moved my first-year graduate courses out a year. Or two, in the case of classical electrodynamics. The scary professor taught it my second year, so I put it off until my third.

Not only did I have to make up some physics and math that first year, but the A part of my BA propelled me across campus into the stacks of Green Library to read the great works of Russian literature in my free time. In translation, of course. What are you thinking? I’m far too lazy to learn Russian.

Anyway, in pursuit of my liberal arts education I learned how to calculate the percentage of DNA shared by relatives. Turns out that's even more useful than partial differential equations in real life. A rough calculation is easy enough. You get half your DNA from each of your parents. Birth mother to me, 0.5. DNA dad to me, 0.5. Each parent also transmits half their genetic material to their other progeny, as their children are known in biological anthropology. So my half-siblings and I share one quarter of our genetically-determined characteristics: 0.5*0.5 = 0.25. Full siblings have two parents in common, so you multiply by two. If I had a full DNA sibling (and many people do), then we’d share 50% of our DNA. Statistically. Your results may vary.

In the Poe calculation, let’s make the simplifying (and likely indefensible) assumption that all siblings were full siblings, and that no one besides EAP married a close relative. Then whichever of EAP’s first cousins was Max’s and my ancestor would have shared 0.5*0.5*0.5*0.5*2 = one-eighth of EAP’s DNA. Remember, the factor of two comes from EAP and his cousin having two grandparents in common.

Have I lost you yet? Every time you go up a step in the family tree, or down a step, multiply by one-half. And at the top of the tree, there’s a factor of two—two parents are shared at the top—but there aren’t any more of those pesky factors of two. So if you count the generations from EAP’s first cousin down to me, and call that N, then the answer to the question of how much DNA I share with EAP is one-half to the Nth power times one-eighth. As Lee would say, easy-peasy. I always reply, lemon-squeezy.

Now let's determine N. According to some hasty lazy internet research, EAP’s grandparents were John and Jane Poe, born in Ireland in the early 1700s. I picture them as frugal farmers. Compact, serious people. Saved enough money by not having to write more than seven letters to capture their full names that they had could afford to emigrate to America, soon after their nine children were born. A tidy sum from the sale of their pre-blight potato farm sewn into the linings of their overcoats allowed them to reconstruct their Irish farm in the new world, make a modest living and raise their family. Their son David was EAP’s father, the one who ditched little EAP right after his wife died.

Let’s fill in the other parts we know, from the other end of history. My paternal grandmother, Mary, was born in 1902, and her father was named George Poe. I’m going to name him George-5, and if you’re following my train of thought, you know why already and can skip to the end. Making the simplifying (and indefensible) assumption that each father was 25 years old upon the birth of his child, then George-5 was born about 1875. His father, George-4, in 1850. George-3 in 1825. George-2 in 1800.

Since EAP was born in 1809, I’m going to call George-2 the first cousin from whom Max and I are descended.

The simplifying assumptions I've made here remind me of the punchline of a joke in which a physicist has to calculate the speed of a race horse. The physicist says, let's start by assuming the horse is a sphere.

Turns out that John and Jane Poe really did have a son named George (aka George-1), born in 1774, which is close enough to 1775 to declare triumph, especially given the gargantuan error bars inherent in this exercise. So George-0 is John Poe from Ireland, sharing the top of the tree of this fanciful calculation with his brave wife, Jane. She of the once-bulky overcoat lining.

Three generations from George-2, EAP’s first cousin, to Mary’s father, George-5, and then two more from Mary to me. One more to Max.

Remember, we’re starting from 1/8, for first cousin. So here’s the result you’ve been impatiently waiting for:

1/8*1/2^5 = 1/2^8 = 1/256 = 0.4%. That means 0.2% for Max.

Calculating statistical DNA percent sounds more scientific, and that's what we've been doing until now. But even more appropriate, given our EAP ancestry, is to calculate this in terms of blood volume. I mean, we’re blood relatives and all. Comes out to 20ml for me and 10ml for Max. Four teaspoons for me and two for Max, for those of you who steadfastly adhere to the archaic Imperial system.

Measuring blood by the milliliter brings to mind a small graduated cylinder in a clean medical lab, devoid of emotional content. Blood by the teaspoon is more EAP.

[Max and I have another ancestor you might have heard of, on my birth mother’s side. Might have heard of. He was a tier-two movie star from the 1940s. Possibly tier three. Handsome, though, in that pre-color way. Do you recognize him?]