Follow-up on DNA testing

In reading my most recent book, I came across a statistic related to the "milkman" problem I referenced in my last post. In this post, I noted that DNA testing for genealogists could potentially raise problems, especially in the future, with the increased use of sperm banks.

The book I am reading now is Dr. Tatiana's Sex Advice to All Creation by Olivia Judson (Metropolitan Books: New York, 2002). Before you jump to conclusions, let me explain that it is a natural history book that discusses genetics and the many ways that plants and animals have evolved to reproduce. Here is a quotation (p. 163-4) that directly relates to the milkmen:

"For example, in England, children usually get their last name from their father. Boys get something else from their father: their Y chromosome. Thus, if all living males bearing a particular last name are the direct descendants of one man, they should all have the same genetic markers on their Y chromosomes. In the absence of infidelity (or adoption), last names and Y chromosomes should match up. One study analyzed the Y chromosomes of men called Sykes, a name that first appears in written records about seven hundred years ago. It turns out that almost all the Sykeses investigated did indeed have the same markers on their Y chromosome, suggesting that most living Sykeses have the same distant ancestor. The rate at which females married to Sykeses were unfaithful (or adopted sons) over the period of seven hundred years is estimated to be 1.3 percent per generation."

Judson references: Sykes C. and B. Irven, 2000. Surnames and the Y chromosome. American Journal of Human Genetics 66: 1417-19.

That's pretty incredible if you think about it. Of course, I can think of any number of possible flaws with the study, and since I haven't read it directly, have no idea how accurate it might be. Still, a 1.3% infidelity rate seems astronomically low. Added up, though, it can create a huge possibility for biological error (never mind all the possibilities for documentary or research error).

Here's the math based on the 1.3% above: a 98.7% chance you are related to your father, 97.4% chance you are related to your paternal grandfather (but 98.7% for the maternal grandfather), etc. There is a 96.1% chance that you are biologically related to your grandparents... yes, the ones listed on your parents' birth certificates.

By the time you hit your ggg-grandparents, there is only a 59.6% chance that you are biologically related to all of them. The only person you can be sure of in this model is your mother's mother's mother's mother.

This means that there is an exponential rate at which you are likely to not be related to your ancestors. Based on the math, in under 2000 years, you are guaranteed to not be biologically related to your father's father's father...

Ironically, of course, there is also evidence that with the world's population size about 2000 years ago, we are all likely to be related somehow. Just not the way we think.

In another similar study, Y-chromosomes and the extent of patrilineal ancestry in Irish surnames, the authors note that: "Notwithstanding differences in their early origins, all surnames have been extensively affected by later male introgession." In other words, although we were all once 'pure' lines descended from one or multiple males (depending on the surname), we're mostly all bastards now! There was about a 50% likelihood of relatedness in this study between two males with the same surname. Not bad, but less than you'd expect without the 'introgession'.

The Genius Factory

I just finished reading The Genius Factory by David Plotz the other day. In brief, it is a summary of a sperm bank that tried to sell sperm from Nobel Prize winners and "geniuses". The author connected a number of the children with their anonymous donors.

I think that the book has some interesting relevancy to genealogy. Or, not so much the book itself, but the topics it covers. For example, there is a chapter devoted to eugenics, which was a huge movement in the early part of the 1900s Basically, eugenics is the belief in engineering "better" human beings through careful breeding. In its worst moments eugenics was a cover for racism and the castration of individuals with disabilities (or murder - see Hitler). "Positive" eugenics focused more on the selection of "fitter families" that could pass on their traits of intelligence or physical attributes to their children. I actually think there is some connection between members of my family and the eugenics movement, which I am exploring, so more on that in another post.

The concept of sperm banks is also an interesting dilemma for family historians. Many of the children conceived by sperm banks were never told. Especially early on, children who were conceived were usually born to couples where the husband was infertile, and then raised as though they were his biological children. Now, things tend to be a little different and banks are working more with lesbians and single women. Still, I think this is an interesting issue.

With the advent of genealogy through DNA, anyone in the future may have difficulty connecting descendants. Siblings may have had different donors. And although the dad might be on the birth certificate and in other documentary records, his DNA won't be a match to his kids' DNA. As someone once said about genealogy, "all it takes is one milkman". This, of course, has always been true. It is definitely one of the limitations of genealogy with or without DNA testing.

Jess's family has an ancestor who was adopted in the mid-1800s (Ella Shaw). She was adopted into the Mikeworth family, appearing with them in every census, beginning when she was just 5 years old. She was born in 1863 in Illinois, and from her death certificate, it seems her father's name was Samuel. Samuel Shaw is just too common a name for me to be able to identify him based on that. However, it is an interesting conundrum to think about. I'm not sure whether her birth family is necessarily all that important. After all, the people who raised her were almost certainly more important to her. Nonetheless, she maintained her birth name, staying a Shaw until she was married (to Lewis Bowman). I could probably track down her father with a little more effort, but am uncertain what to do about this adoption/birth family business. Do I research the Mikeworth family? How important is the biological connection?

This bears an interesting relationship to our nuclear family, where Jess is not Asa's biological mother. Nonetheless, she is clearly his mother, and I felt it was equally important for me to investigate her family tree (although I fully expect him to have NO interest in these topics).