1066 is the time of the Norman Conquest. There were 1.11 million people living in England at that time. People living in England today can find ancestors in 86% of them.
1215 found 2.5 million people living in England. Today's English population can find ancestors from 1300's English population.
Go back 10 generations or 250 years to the year 1760 AD and you should have 1,024 ancestors!
What you have done is that you have 2 parents making 4 grandparents, and the number keeps doubling.
This all proves that people were marrying their cousins because the tree gets smaller the more you go back in history. We are cousins with just about everyone. The reason is that if you go back 30 generations or 750 years to the year 1260 AD, you would have 4,356,616 ancestors and that's more than the population at that time, even if everyone were marrying 2nd cousins. So there has been a lot of inbreeding among families in the past. We knew that Egyptian royalty practiced this, and the Bible shows that our forefathers were marrying cousins then, but I hadn't realized it went on in later history.
I'm lucky to have found a great genealogist living in England who has taken our shared family tree line back to John Henwood born in 1538 in Medstead, Hampshire, England. Most every male on the tree has come from Hampshire. Another line of Henwoods come from Cornwall from the village, Henwood. We went back 13 generations or rather 13 male fathers to get there. I went from Charles, Charles, Henry, Henry, John, John, John, Robert, William, William, William, Guy, and then John. I'm skipping the 3 live Henwoods in the count, which would really make 16 generations.
Resource: family tree magazine March 2011 page 10 Fuzzy Math.