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.