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NOTE

How Many Ancestors Do You Have?

NOTE: This is a repeat of an article I published 2 years ago. The subject popped up again recently so I decided to republish this article again for the benefit of those new readers of this newsletter who did not see the original article. I also made a couple of minor updates to  the original article.

A newsletter reader asked a simple question this week that generates a longer answer:

How many individuals does it take to make up 42 generations? Is there a website or other source that would help me calculate the answer?

I am sure there are such web sites, but you can also calculate the same numbers within a few seconds by using Excel or any other spreadsheet. I used a spreadsheet to generate the following:

# of generations

Total ancestors

1

0

2

2

2 parents

3

6

2 parents + 4 grandparents

4

14

2 parents + 4 grandparents + 8 great-grandparents

5

30

2 parents + 4 grandparents + 8 great-grandparents + 16 great-great-grandparents

6

62

2 parents + 4 grandparents + 8 great-grandparents + 16 great-great-grandparents + 32 great-great-great-grandparents

7

126

and so on and on…

8

254

9

510

10

1,022

11

2,046

12

4,094

13

8,190

14

16,382

15

32,766

16

65,534

17

131,070

18

262,142

19

524,286

20

1,048,574

21

2,097,150

22

4,194,302

23

8,388,606

24

16,777,214

25

33,554,430

26

67,108,862

27

134,217,726

28

268,435,454

29

536,870,910

30

1,073,741,822

31

2,147,483,646

32

4,294,967,294

33

8,589,934,590

34

17,179,869,182

35

34,359,738,366

36

68,719,476,734

37

137,438,953,470

38

274,877,906,942

39

549,755,813,886

40

1,099,511,627,774

41

2,199,023,255,550

42

4,398,046,511,102

43

8,796,093,022,206

44

17,592,186,044,414

45

35,184,372,088,830

46

70,368,744,177,662

47

140,737,488,355,326

48

281,474,976,710,654

49

562,949,953,421,310

50

1,125,899,906,842,620

In 42 generations you have more than 4 trillion ancestors!

Of course, that is far more than the total of all the people who ever lived on the face of the earth. The fact is that there are not 4 billion unique ancestors. We all have multiple lines of descent from many individuals. That is, if we were able to create a complete pedigree chart for 42 generations or more, we would see the same individuals appearing at multiple locations on the same chart.

This is often called “pedigree collapse.” See Wikipedia at https://en.wikipedia.org/wiki/Pedigree_collapse for more information about “pedigree collapse.”