How many ancestors do you have puzzle

[mortieau]

 I guess I'm a bit old fashioned I like to make my family trees on large sheets of paper, only one of the many branches I was able to get to 1530's but when I tried to put blank spaces for all the other branches that I've yet to fill in I found by the earlier 1500's I would theoretically have had 4096 direct ancestors.

This got me to wondering, as by the early 13th century the number of direct ancestors is about 2 million, so as this number grows  the world population is getting smaller as we go back in time, what happens when the number of direct ancestors exceeds the world population?

Or am I missing something?

Best
John

[Ruskie]

Some interesting reading here:
http://www.bpears.org.uk/Misc/AncestorParadox/

... and some more at the bottom of the page ...

[stonechat]

Yes it'[s interesting

I have two examples - one of third cousins marrying and one of first cousins marrying

[Nick29]

It has been said that most families in Europe are related, because of this phenomenon.

[Rishile]

An interesting thought and very interesting article but I don't agree with the numbers, I'm afraid.

If you have just one person showing twice in your direct line in every generation from the fifth generation going backwards, the effect at the 30 generations mark will be a difference of 268,402,688.  That doesn't necessarily mean cousins marrying cousins.  It could be totally different lines being married generations before.  The further back you go, the more chance there is of more than one occurance in each generation so this changes the figures again.

What you need to bear in mind is that one two people who have already shown in your tree get married, one line stops completely because they merge.

Rishile

[johnxyz]

One of my grandfathers is from a small hill village in Derbyshire. There are 
good records for there and the surrounding area, so I can trace most of his lines back to his 6 great grandparents, at which point there should be 256 people. Given the number of lines that inter-marry - and there is only 1 direct cousin to cousin marriage - he has at most 192 ancestors.

Drawing the tree, I have 6 points where the descent from a couple can proceed through either of two of their children.

It also creates the problem of describing couples who are, for example, both my 4 great-  and 5 great- grandparents.

[Marmalady]

In my husbands tree there is a family where not only the two parents, but 3 out of the 4 grandparents all have the same surname. And even for the 4th  that surname occurred a generation or so previously
Cuts down drastically on the number of ancestors!

[mortieau]

Thanks for all the answers especially Ruskie for those 3 articles by Brian Pears, who asks the same question but more informatively.

So even though it still stays somewhat of a paradox, the growth of the number of ancestors was  lessened by families constantly over many generations inter-marrying. Also to a lesser extent people of other regions were being added to pool of possible ancestors.

My wife whose ancestors came from southern Russia & Ukraine showed me a genealogical study done recently for the male Y chromosomes there and found that over 50 % of the population had Genghis Khan as an ancestor, but then Genghis supposedly had 40 sons, so he had a good start.

Best
John

[Simon G.]

My wife whose ancestors came from southern Russia & Ukraine showed me a genealogical study done recently for the male Y chromosomes there and found that over 50 % of the population had Genghis Khan as an ancestor, but then Genghis supposedly had 40 sons, so he had a good start.

Very much the same is true with regards to Charlemagne, with his at least 18 children by 8 wives and/or concubines.  I'd put good money on each and everyone posting here to be a descendant of his in one way shape or form.