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According to a post on Slashdot:

Every single elected president - INCLUDING Barack Obama, has a genealogy related to President George Washington.

Note I did say Elected President. Gerald Ford is (as of yet), not known to be related to George Washington.

Barck Obama is George Washington's 9th cousin, 6 times removed. Yes, this is through his white mother.

From what I can tell, the least connected elected President was Martin Van Buren - 17th cousin thrice removed.

Also, President William Henry Harrison was related by marraige, not by blood.

my source [geni.com]

This seems to be a rather extraordinary claim.

I'm skeptical of whether this is in fact an extraordinary event. If it is indeed extraordinary I am skeptical of the source.

The claim may not be particularly extraordinary if many or most of American descent are related to George Washington. Are American presidents more related to George Washington than Americans in general? What about the American population as a whole?

In any case, does the source adequately support the conclusion?

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    Define "related" for the purposes of this discussion. Does mitochondrial Eve count? – dmckee Dec 28 '11 at 1:36
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    I agree with @dmckee...I am related to every US president and every Russian head of state. You need to add some limits to 'related' – Rory Alsop Dec 28 '11 at 9:56
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    I assume the intention here is "related"=="can trace a geneological relationship." So for this to be true, there would need to be a known, researched/documented relationship between every president and Washington, not just for the relationship to exist (which is trivial). – Ziv Dec 28 '11 at 12:11
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    @BrianM.Hunt basic maths here. If we can assume an average total fertility rate of 4 children per woman, given that we go back a few hundred years, then we can join 60 million people in a family tree with (at least) 13 degrees. Some presidents are 17 degrees separated, so it's mathematically hardly surprising. – Sklivvz Dec 30 '11 at 10:08
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    @BrianM.Hunt It is not the claim of geni. They have a cluster of 60 million people which includes the presidents and they don't find it surprising at all, and neither do I. The approximate minimum depth of that cluster must be around 13 generations (in the ideal case) or more (in the real case). Some of the presidents are 17 degrees away or so... The numbers, and the claim, are completely unsurprising, and I don't really know: do you expect us to double check the genealogy of all the presidents? – Sklivvz Jan 1 '12 at 2:17
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Probably correct, but not certainly not surprising

If it is indeed extraordinary I am skeptical of the source.

The source is reliable and the event is not extraordinary.

Like many other sites Geni relies on census records, birth certificates, marriage licenses. And famous people tend to receive an extra level of attention.

The claim itself is rather liberal in its allowances:

  1. As a seventeenth cousin, Van Buren's common ancestor would have been over 400 years earlier (1300s).

  2. The claim is not limited to blood relatives. For example, it states that James Madison is George Washington's "co-brother-in-law" (wife's sister's husband).

With such wide parameters, it's not surprising that all elected U.S. presidents would be related to the first.

Relationships can cover a lot of ground quickly:

  • Genghis Khan who died less than 800 years ago is famously an ancestor of 8% of a large area of Asia.

  • A popular theory with very modest experimental evidence is that everyone is connected by only six direct family/friend/co-worker/associate relationships.

This claims permits spanning dozens of relative links including marriage of powerful people in a single country.


FYI:

  1. In addition to Harrison's non-blood relation mentioned on Slashdot, Madison and Taft are also listed by Gemi as related through marriage.

  2. Though out of scope at the time the claim was made, Donald Trump is also related to George Washington.

  3. Gemi now has Ford's adoptive mother as George Wasington's fifth cousin five times removed.

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    Another way to express how remote a 17th cousin is, is to point out that without "pedigree collapse" (the same individual being your ancestor via multiple paths), you would have 262,144 sixteen-greats-grandparents, and every one of their descendants would be a 17th cousin or closer. – IMSoP Oct 30 at 15:05

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