DNA, Genealogy And The Search For Who We Are

I might suggest that an article by Alva Noë in the NPR web site should be required reading for all genealogists. He writes:

  • You share no DNA with the vast majority of your ancestors.
  • You have more ancestors — hundreds a few generations back, thousands in just a millennium — than you have sections of DNA.
  • You have 64 great-great-great-great-grandparents — but if you are a man, you share your Y-chromosome with only one of them.
  • The amount of DNA you pass on to your descendants roughly halves with each generation. It is a matter of chance which of your descendants actually carry any of your DNA.
  • It can be demonstrated that 5,000 years ago everybody alive was either the common ancestor of everyone alive today, or the common ancestor of no one. At this point in history we all share exactly the same set of ancestors.

In other words, everyone alive today is related to everyone else alive today. We are all distant cousins of each other.

You can read Alva Noë’s article at http://goo.gl/kh6bUb. The article also has a link to a talk given by Mark G. Thomas at the Who Do You Think You Are Live conference last year in Birmingham, England that I attended and I found the talk to be fascinating.

NOTE: Alva Noë is a philosopher at the University of California, Berkeley, where he writes and teaches about perception, consciousness and art. He is the author of several books, including his latest, Strange Tools: Art and Human Nature (Farrar Straus and Giroux, 2015).

8 Comments

I wanted to listen to Mark Thomas, but the audio is very bad. Don’t suppose it is written out somewhere ?

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Thank you so much for sharing this. I am frequently asked for help by people claiming to be related to Laura Ingalls Wilder, since interpreting her life and work is one of my chosen specialties as an historian.

I cannot tell you how often people insist on claiming the relationship when, to the best we can estimate, it is one falling along the lines of “7th cousins, 5x removed” or the like. These people often go on to make the assertion to anyone who will listen that they somehow “know” a good deal about what “must” be true of LIW’s immediate family–by basing an assumption on their own immediate family. Sometimes they also associate my name with helping them “discover” this “truth” about their favorite historical figure.

Every time I get an inquiry such as this, I cringe. I know what is likely to happen next; perhaps I should have a policy of non-assistance on these requests?

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I totally agree that there was realistically only a small number of people. Once groups left who did they mate with? Relatives. Course as time goes we start to branch out find other people(who most likely are related in some way).
People don’t like to think that their ancestors slept with and had children with close family.
I wonder how the Professor is welcomed by people outside his realm. Any thoughts?

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Mark Thomas can also be heard on this (always excellent) Infinite Monkey Cage podcast, What is Race? http://www.bbc.co.uk/programmes/b06ybg84

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I question this DNA any ways. Did all the people listed on your list of ancestors (
DNA) have had the test?!

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It’s quite apparent that Alva Noë is not familiar with the way genetic genealogy is used in practice — one of many tools, and one which is endorsed by such respected experts as Elizabeth Shown Mills
https://familysearch.org/learn/wiki/en/Elizabeth_Shown_Mills

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I posted a comment on the article itself but I’m repeating it here because it’s got somewhat buried. I’m one of the co-authors of the material on the UCL website on which you have based the content of this article. It is not the whole industry that is being criticised but only those companies that make misleading claims about deep ancestry from Y-DNA and mtDNA haplogroups. The criticisms that have been voiced on our website are largely related to one specific company that has dominated the media coverage in the UK for the last few years. Sadly their misleading and sometimes ludicrous claims have only served to damage the whole industry and give people a false sense of what to expect from a DNA test. Mark Thomas made it quite clear in his lecture at WDYTYA Live that DNA testing can be used legitimately for genealogical purposes and we also make this quite clear on our website. Indeed, the vast majority of people who take DTC tests are doing so not to find out about their ancestry from thousands of years ago but to find matches with close cousins in the genetic genealogy databases. This information is used in combination with genealogical research to draw conclusions about relationships and surnames within the last 500 years or so. It is the combination of DNA evidence with genealogical research – what we call genetic genealogy – that is so powerful. There are also thousands of adoptees and foundlings who are using DNA testing to find out about their biological families. They are often finding matches with previously unknown close cousins and sometimes even siblings and parents in the databases. You might like to read my blog post for Sense About Science which explains how these tests work: http://www.senseaboutscience.org/blog.php/41/sense-about-genealogical-dna-testing

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From the Mark Thomas article:
” This means we don’t have to look back much more than around 3,500 years before somebody lived who is the common ancestor of everybody alive today.
And perhaps most surprisingly, it has been reasonably estimated that around 5,000 years ago everybody who was alive was either the common ancestor of everybody alive today, or of nobody alive today; at this point in history we all share exactly the same set of ancestors.”

I don’t know, this sound dubious to me. For instance, say there is an American Indian who lived 5000 years ago here in what is now the United States and that he left many descendants that are alive today. How could this man be an ancestor of everyone alive today? Did his descendants keep travelling across the oceans to Europe and Asia and Africa to help populate these continents? I think these theories keep being perpetuated by numbers crunchers who drastically under estimate the amount of repetition there is in our families trees. People in a community kept marrying other people in the same community so that everyone is related to everyone else in multiple ways on both maternal and paternal lines. So our ancestors repeat and repeat.

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