*How we are all descended from Royalty

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LornaCraig
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How we are all descended from Royalty

Postby LornaCraig » 20 Nov 2017 12:22

I have come across an entertaining article by Adam Rutherford, author of “A Brief History of Everyone Who Ever Lived”. The article is an amusing read, if you have a few spare minutes.

He refers to the British TV series Who Do You Think You are, in which a number of featured celebrities have been shown to be descended from Royalty. He demonstrates that for someone with broadly British ancestry, born in the 1970s, the chances of NOT being descended from royalty are vanishingly small. Of course, most of us just have to rely on the mathematical proof because the paperwork is missing!

The piece was written for Waterstones (bookshop) as part of their promotion for Rutherford's book. I should make it clear I have no connection with the author or with Waterstones.

It can be found at https://www.waterstones.com/blog/family ... to-royalty
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Re: How we are all descended from Royalty

Postby tatewise » 20 Nov 2017 12:56

I think that a mathematical analogy can presumably prove that you are related to everyone that ever lived.
If you think about it for a moment, then it has got to be 100% true, as all humans must be related albeit mostly very distantly.
Mike Tate ~ researching the Tate and Scott family history.

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Re: How we are all descended from Royalty

Postby LornaCraig » 20 Nov 2017 13:19

Yes indeed. But this article demonstrates that a direct line of descent from royalty is almost a certainty in just 20-odd generations. That's probably a lot closer than most people would expect.
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Re: How we are all descended from Royalty

Postby tatewise » 20 Nov 2017 14:00

Yes, probabilities throw up interesting statistics.
If you are at a gathering, such as a party, of about 30 or so people, then the chances are about 50:50 that somebody will have the same birthday as yours.
Not the same year, but just the same day of the year, unless of course if you were born on 29th Feb!
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Re: How we are all descended from Royalty

Postby johnmorrisoniom » 20 Nov 2017 15:05

To re-enforce Mikes point about Birthdays. A slightly amusing incident.

When I was on my first year of an Electrical and Electronic Engineering Degree Course, one of the subjects that we had to take was Statistics.
The lecturer wanted to demonstrate the birhday statistic (They were 40 of us in the class).
Starting at the back of the room, each person in turn, shouted out his birthday, anyone whose birthday was the same, put their hand up.

3 students in we already had one match. sixth student in announced 8th March, at which point 6 of us put our hands up. QED as they say.

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Re: How we are all descended from Royalty

Postby Peter Collier » 20 Nov 2017 16:41

I believe some studies have postulated that you need go back only 3000 years for there to be one single person ancestral to every person alive on the face of the earth today. Restrict yourself to Europeans, and you need only go back as far as the middle ages.

The coomon ancestors for mtDNA and YDNA are further back - about 200k to 300k years ago, I think I read.

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Re: How we are all descended from Royalty

Postby DavidNewton » 20 Nov 2017 18:02

More years ago than I care to remember I read and thoroughly enjoyed a book by Darrell Huff entitled "How to lie with Statistics". It was published in 1954 so it may seem a bit dated now but the principles remain the same and the advertising industry was then and still is the expert on the misleading statistic.

http://www.horace.org/blog/wp-content/u ... 4-Huff.pdf

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Re: How we are all descended from Royalty

Postby AdrianBruce » 20 Nov 2017 22:37

tatewise wrote:... If you are at a gathering, such as a party, of about 30 or so people, then the chances are about 50:50 that somebody will have the same birthday as yours. ...

I have a feeling that you are mis-remembering this. I think that the story is that in a party of about 30 or so people, then the chances are about 50:50 that there will be two people (any two) who have the same birthday.

The probability doesn't specify who the 2 are - you really would need over 180 people to get a better than evens chance of someone with your birthday - it's the fact that we don't care who has the same date that brings the probability up with the smaller numbers.

This is so far as I remember - I never liked stats. I could never really work out what a standard deviation was, e.g., but the formula was easy enough. A case of "Shut up and calculate..."
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Re: How we are all descended from Royalty

Postby AdrianBruce » 20 Nov 2017 22:49

The dodgy bit of logic in his reasoning is
You have two parents, and they had two parents and so on, two by two, so the number of ancestors doubles each generation working up your family tree, meaning that by 1600, one person should have 32,768 ancestors. This assumes full outbreeding, which is very unlikely – we’re all inbred over a long enough period – but for our purposes makes little difference.


My emphasis. The italicised bit is pedigree collapse. How does he know it makes little difference? I can envisage a picture of my tree ending up with lots of whorls where people in Devon breed with their nth cousins in Devon, people in Staffordshire breed with their nth cousins in Staffordshire, etc., and all the massive explosion - isn't massive at all.

If there is sufficient mixing, then indeed it becomes a racing certainty that we are all descended from Edward III - but I wonder how many of us have that racing certainty?
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Re: How we are all descended from Royalty

Postby tatewise » 20 Nov 2017 23:42

You are probably correct about the birthdays at a party, but the number of people is much smaller that I recall.
The calculation goes like this.
The probability that first two people have different birthdays is 364/365.
The probability that a third person also has different birthday is 364/365 * 363/365.
That continues for successive people multiplying by 362/365 * 361/365 * 360/365 etc.
i.e.
364*363*362*361*360 ... 340*339*338*337*336 divided by 365 to the power 29 assuming 30 people in party.
That is 364 factorial divided by (365-30) factorial divided by 365 ^ 29
364! / 335! / 365 ^ 29 = 0.293 probability that all have different birthdays so about 0.717 that two have same birthday.

With a party of 23 people that becomes:
364! / 342! / 365 ^ 22 = 0.492 probability that all have different birthdays so about 0.508 that two have same birthday.

Thus you only need 23 people for the probability to be about 50:50 that two have same birthday.
I suspect the figure of 30 is popular because if taking monetary bets you are likely to win about 70% of time!
Mike Tate ~ researching the Tate and Scott family history.

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Re: How we are all descended from Royalty

Postby DavidNewton » 21 Nov 2017 09:52

AdrianBruce wrote:The dodgy bit of logic in his reasoning is
You have two parents, and they had two parents and so on, two by two, so the number of ancestors doubles each generation working up your family tree, meaning that by 1600, one person should have 32,768 ancestors. This assumes full outbreeding, which is very unlikely – we’re all inbred over a long enough period – but for our purposes makes little difference.


There are dodgy assumptions in this article but we need to recognise that this is a fun 'back of a napkin' calculation which you might do over a few glasses of wine and is being used as a book promotion to attract interest - succeeded hasn't it? The reference to two experts who did this calculation and came up with essentially that same number is also a standard advertising ploy "We spoke to an independent expert ... "

The dodgy assumptions that spring to mind
1. The calculation of the number of of descendants of Edward III in 1600CE is simply based on an estimate of the number of generations, 6, on from the great great grandchildren and the assumption that each of them will have 64 descendants at that time. May or may not be true
2. The proportion of the population who were direct descendants in 1600 is based on the assumption that all his descendants were living in Britain at the time. Almost certainly false. The descendants will be spread thoughout Europe as cross-country intermarriage is how power is maintained.
3. The average of 25 years per generation is not only an 'out of the hat' number with no indication of how it is obtained but also has an unspecified "average" within it.
4. Finally the problem mentioned by Adrian. Ignoring marriages between relatives clearly has an effect but an effect which is difficult to quantify hence, ignore it.

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Re: How we are all descended from Royalty

Postby LornaCraig » 21 Nov 2017 10:49

Yes, I thought it might stir up some discussion here! I agree there are some dodgy assumptions. However the main message is still valid: a celebrity who is 'gobsmacked' on being told they are descended from Edward III (or William the Conqueror or...) is missing the point. They are among many millions of others. What sets them apart is the fact that they have a paper trail (parchment trail?) to prove it.
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Re: How we are all descended from Royalty

Postby ColeValleyGirl » 21 Nov 2017 12:03

LornaCraig wrote:What sets them apart is the fact that they have a paper trail (parchment trail?) to prove it.


That, and the team of professional genealogists who have done all the hard work for them...

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Re: How we are all descended from Royalty

Postby AdrianBruce » 21 Nov 2017 14:23

ColeValleyGirl wrote:... That, and the team of professional genealogists who have done all the hard work for them...


Oh Helen - so cynical, I thought they did it all themselves! ;)

Actually, I do wonder if any of the slebs on WDYTYA? actually pick up their Apples (always an Apple!) and start going off-piste with their own research?
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Re: How we are all descended from Royalty

Postby AdrianBruce » 21 Nov 2017 14:27

tatewise wrote:... Thus you only need 23 people for the probability to be about 50:50 that two have same birthday. ...

Well I'm glad you did the calculation... I'd seriously forgotten how to do it. (Actually I did think that the number was about 2 dozen but you'd typed it so confidently that I didn't question the figure, just the premise!)
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Re: How we are all descended from Royalty

Postby Gowermick » 29 Nov 2017 08:35

DavidNewton wrote:More years ago than I care to remember I read and thoroughly enjoyed a book by Darrell Huff entitled "How to lie with Statistics". It was published in 1954 so it may seem a bit dated now but the principles remain the same and the advertising industry was then and still is the expert on the misleading statistic.

http://www.horace.org/blog/wp-content/u ... 4-Huff.pdf

David


I came a bit late to this discussion, but David’s comment reminded me of current Advertisements , especially common for beauty products, when they make claims like “80% of women find an improvement using this product” Followed in very small print “based on a sample of 79”! Sadly, people fall for this type of hype or should I say claptrap :) !
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Re: How we are all descended from Royalty

Postby Tony Jones » 13 Mar 2018 09:01

I was given the Adam Rutherford book for Christmas; an interesting read but he does spend a lot of time debunking various myths. He seems very scathing of DNA tests for family history, and I got the impression he wasn't too impressed with genealogy at all. I suspect he is used to thinking in 10s of 1000s of years and thinks looking back a few hundred years a bit irrelevant, certainly in terms of his work.

In the book he refers to the same mathematical proof to confirm we are all descended from Charlemagne (and everyone else from before)
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Re: How we are all descended from Royalty

Postby AdrianBruce » 13 Mar 2018 13:30

Tony Jones wrote:... I got the impression he wasn't too impressed with genealogy at all. ...

Of course, you need the boring genealogy bit to prove that Charlemagne had any descendants at all. If he didn't, all bets are off. (Apparently he had lots of descendants - it says so in this book on FamilySearch :D )

Slightly less frivolously, I did see an posting on Dick Eastman's Blog a while ago, where someone tackled the issue of mixing. They divided an arbitrary population up into 10 arbitrary sub-populations with minimal mixing and assigned a suitably low probability to any one ancestor coming from outside that sub-population. Even when that suitably low probability was something like 1 in 1 million, the fact that you have a potential million ancestors after only some 600 years meant that there was actually a high probability that 600y ago, you had 1 ancestor from another sub-population. After that, their ancestry in that other sub-population bloomed until after 1200 years your ancestry in that sub-pop became close to total as well. Takes a while to move over the sub-pops, so the chance of me being descended from the First Emperor of China is probably not high (if he had descendants). But aside from that, eventually you get there. Wherever and whenever "there" is.
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