
How many genetic ancestors do you have? - danieltillett
http://burtleburtle.net/bob/future/ancestors.html
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SideburnsOfDoom
> The number of genealogical ancestors you have n generations is 2n: 2
> parents, 4 grandparents, 8 great-grandparents, and so forth. The only way to
> have fewer is if some of them are the same person.

They leave out that this effect that "some of them are the same person" is
inevitable, even pervasive, past a few generations. Never mind that the number
of "genealogical ancestors" rapidly becomes larger then the number of humans
alive at the time, it's almost certain that your * 10 grandparents didn't
travel much, so existed as part of a far smaller sheltered gene pool.

~~~
maxerickson
At the bottom, it says _You had a trillion genealogical ancestors 40
generations back, which far exceeds the total number of people who have ever
existed, so most of your ancestors appear many many times in your genealogical
tree._

The links in my other comment talk a bit about measured genetic similarity
(which should imply relatedness), it turns out there is a lot of mixing.

------
danieltillett
I posted this because I have always wondered what the answer to this question
was, but could not do the maths - it is very hard and can only really be done
by simulation as Bob as done.

I suspect that the 46,000 genetic segments is an approximation, but it should
not mess up the calculations too much if this is wrong. The truly amazing
thing is how few real ancestors you have out of the possible number.

~~~
maxerickson
I posted one of the articles linked in this article a while back (without much
discussion). The author did stop by and post a link to this article, which
talks a little more about the consequences:

[http://phenomena.nationalgeographic.com/2013/05/07/charlemag...](http://phenomena.nationalgeographic.com/2013/05/07/charlemagnes-
dna-and-our-universal-royalty/)

and this paper, which uses DNA analysis to look at ancestry in Europe:

[http://www.plosbiology.org/article/info:doi/10.1371/journal....](http://www.plosbiology.org/article/info:doi/10.1371/journal.pbio.1001555)

~~~
vsbuffalo
Here's the thread if anyone is interested:
[https://news.ycombinator.com/item?id=7539143](https://news.ycombinator.com/item?id=7539143)

------
apaprocki
I highly recommend using an existing DNA service (I use FTDNA) to sequence the
Y chromo and/or MTDNA of your living direct relatives (where it makes sense..
only one Y for male line, etc) because the samples are kept in storage and you
can use them for sequencing later as technology drastically ramps up. My Y
data is available to researchers and my and my father's MTDNA are in Genbank.
Genetic anthropologists use the data to fine tune our knowledge of historical
population movements. The current theory is that I am descendent from the
Vistula Veneti. I just wish more people had an interest so that there were
more data samples. You can't just go around demanding peoples' DNA, even if it
has nothing to do with the parts that influence your health.

~~~
thaumasiotes
Out of two stylized models of the world:

    
    
        1. Every part of your DNA influences your health
    
        2. There is an identified portion of the human genetic code
           (including mtDNA) which has no effect on health
    

you'd have to be crazy to believe in model #2.

