Do you know how many ancestors you have? Of course not. Let’s simplify the question: How many ancestors do you have in the past one thousand years? Many people do not know the answer to that question. Care to guess? (The answer is given below but please don’t peek just yet.)

The number of ancestors is simple to calculate as it is a simple mathematical progression: every person has two parents, four grandparents, eight great-grandparents, sixteen great-great-grandparents and so on. The number doubles with each generation. As you go back in years, the numbers soon become very large.

For this example, I have assumed that a new generation appears on an average of every twenty-five years:

Number of Ancestors

Generation Number # of Years Before Your Birth Number of ancestors in that generation Total ancestors (this generation plus all later generations) 1 -25 2 2 2 -50 4 6 3 -75 8 14 4 -100 16 30 5 -125 32 62 6 -150 64 126 7 -175 128 254 8 -200 256 510 9 -225 512 1,022 10 -250 1,024 2,046 11 -275 2,048 4,094 12 -300 4,096 8,190 13 -325 8,192 16,382 14 -350 16,384 32,766 15 -375 32,768 65,534 16 -400 65,536 131,070 17 -425 131,072 262,142 18 -450 262,144 524,286 19 -475 524,288 1,048,574 20 -500 1,048,576 2,097,150 21 -525 2,097,152 4,194,302 22 -550 4,194,304 8,388,606 23 -575 8,388,608 16,777,214 24 -600 16,777,216 33,554,430 25 -625 33,554,432 67,108,862 26 -650 67,108,864 134,217,726 27 -675 134,217,728 268,435,454 28 -700 268,435,456 536,870,910 29 -725 536,870,912 1,073,741,822 30 -750 1,073,741,824 2,147,483,646 31 -775 2,147,483,648 4,294,967,294 32 -800 4,294,967,296 8,589,934,590 33 -825 8,589,934,592 17,179,869,182 34 -850 17,179,869,184 34,359,738,366 35 -875 34,359,738,368 68,719,476,734 36 -900 68,719,476,736 137,438,953,470 37 -925 137,438,953,472 274,877,906,942 38 -950 274,877,906,944 549,755,813,886 39 -975 549,755,813,888 1,099,511,627,774 40 -1000 1,099,511,627,776 2,199,023,255,550

Answer to the earlier question: If we assume that there is a new generation every twenty-five years, an ancestor born 1,000 years before you would be 40 generations removed from you. You would have 2,199,023,255,550 (that’s 2 trillion, 199 billion, 23 million, 255 thousand, 550) unique ancestors born in the previous 40 generations, assuming no overlap (that is, none of your ancestors were cousins to other ancestors).

1,000 years doesn’t even take you back to the years in which Charlemagne lived! (April 2, 742 AD to January 28, 814 AD)

Now, how many ancestors have you had in the past 10,000 years? 100,000 years? I’ll leave it to you to figure out the mathematics involved. However, the answers obviously are huge numbers!

There is but one problem: all of these numbers are far more than the total number of people who ever lived on the face of the earth.

The reality is that all families can find lots of cousins somewhere in the limbs of the family tree, resulting in the same ancestor(s) showing up in multiple places in the pedigree charts. Ask anyone who has done French-Canadian genealogy or has researched any families that lived for generations in one small village almost anyplace on earth.

Obviously, you and everyone else have cousin marriages in your ancestry, resulting in individual ancestors showing up in multiple places in your family tree.