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Jul 9, 2021

How Many Ancestors Do You Have?

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.

Jul 9, 2021

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