A Daunting Thought

[adak576]

How many forebears did you have ten generations ago?  I'm not talking about collectively.  I mean in that one generation, your Great to the Eighth grandparents? 
Think about it.  A 'normal' generation is 25 to 30 years.  So, going back ten generations takes you to 1700-1750.  Not so far.  If by some small chance you were to trace all your ancestors back that far, and, if, by some very, very small chance, there had been no intermarriage or no duplication of ancestors, you would have identified one thousand men & women.  In that single generation! 
If by some even more remote chance you were to push back another ten generations, the number of your Great to the Eighteenth grandparents increases to one million people. 
If you were to spend one minute on each of these people, 8 hours a day, 5 days a week, it would take up one year of your life to add them to your family tree.   
Better get busy folks!

[stanmapstone]

If one goes back 40 generations, one has a trillion ancestors! the world population of humans has never remotely approached that number. The assumption is that all the ancestors in your tree are distinct. What is happening is repetition of ancestors, that is, the same ancestors appearing over and over again in a pedigree. Repetition usually appears within the first ten generations, and the further back one goes, the more repetition one finds. See
http://www.google.com/search?sourceid=navclient&ie=UTF-8&q=%22pedigree+collapse%22

Stan

[Mort29]

even more of a conundrum 

http://www.bpears.org.uk/Misc/AncestorParadox/

[Nick29]

If one goes back 40 generations, one has a trillion ancestors! the world population of humans has never remotely approached that number.

Yes, that's true, Stan.  And, if your family has never strayed from the UK, then you don't have to go very far back in generations before the number of people in the tree exceeds the number of people in the UK, so it's pretty obvious that (with the exception of people who recently emigrated here from other continents) most of us are related, often more than once.

I was trying to explain this to someone who thought it was possible to pinpoint family origins using DNA only a couple of weeks ago 

even more of a conundrum

http://www.bpears.org.uk/Misc/AncestorParadox/

I think I read somewhere that as many as 60% of the population have fathers who don't appear on their birth certificate.   If that is true, why are we all bothering with this genealogy lark ? 

[stanmapstone]

When I first started researching I was told that the only true line to follow was the female one, as usually there is no doubt about who the mother was!
A piece of trivia, an 'agnatic' line of descent is one entirely through males, and a 'cognatic' line of descent is one entirely through females. An 'Agnate' is a relative in the male line from a common male ancestor, related on the father's side, and a 'Cognate' is a relative in the female line from a common female ancestor, related on the mother's side.

Stan