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.

 

12 Comments

I have always figured that each generation was at 20 years not the 25. I can go back 10 generations to Switzerland and his birth date was 1626 and mine is 1946, only 320 years difference. Therefore the 20 years idea seems to be in error. Nice number anyway.

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    —> I have always figured that each generation was at 20 years not the 25.

    I suspect that varies a lot by ethnic groups. In my own ancestry, I find that French-Canadian girls often got married at 15 or 16 years of age although their husbands typically were about 10 years older. However, my New England ancestors, with families that came from England, typically got married in their early to mid 20s.

    Then you realize in the days of large families, these families often continued to have children for 20 years, sometimes longer. For instance, my own grandmother was 15 years old when she got married and then she and my grandfather continued to have 16 children over the next 28 years. (They had grandchildren older than the youngest of their own children. My brother was older than 2 or 3 of his aunts and uncles.) So I think the average age has to be based on the parents’ ages when children were born, not on the marriage dates of the parents. Even with my French-Canadians, I suspect the AVERAGE age of the parents when their children were born was probably 25, maybe older.

    In your example of 10 generations over 320 years, that equals an average of children being born to 32-year-old parents. Obviously, that’s an average. Many times the age of the parents was undoubtedly higher or lower.

    Liked by 2 people

Fantastic job in explaining this. I have tried to explain it several times but you have done it much better. Your chart help tremendously. This also explains why just about anyone who does the research will find many famous people they are related to in their ancestry. With that large a number of ancestors there has to be many that are famous. Thank you.

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Oh! Thank you…seeing this is so very helpful and makes sense. While there will obviously be differences, this is a terrific bell-weather for calculating generational ancestors.

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The best average age per generation to use might even be longer than 25 years. See: https://isogg.org/wiki/How_long_is_a_generation%3F_Science_provides_an_answer

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    Very good article.

    However, to further complicate the calculations, I suspect that the number of one’s children is a function of one’s place in the birth order. Perhaps first born children, traditionally being more likely to inherit the bulk of their parents’ wealth, were seen as more attractive suitors and better able to begin procreating sooner and were better able to support larger families. Children born later in the birth order, on the other hand, stereotypically going into the military or clergy, would have had fewer children on average.

    The result would seem to be that while the average age of one’s parents at one’s birth would be as stated in the article, the average duration of a generation would be slightly less. I wonder if the Icelandic or other data sets offer enough resolution to confirm such a trend.

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While some cultural groups may be different, in my experience with Southern families, women had children, on average, for 22 years, from about age 20 until they turned age 42. Yes, some women had a baby after age 42, but the average is 42 when you look at many women. If you are estimating generations, you should use a middle number in that range of 22 years — 31 years for women. On average, men had their children from age 25 through 47, placing the middle for them at 36. A much better estimate for generations is 33 years. Twenty-five is too low a number. Your ancestors are typically going to move back and forth between being an early child in the family and being a late or last child. Of course, if your line is the first child of the first child of the first child, your generational number will be low. But on the other hand, if your line is the last child of the last child, etc, your generation number will be high. Go for the average. When you are looking at 200 or 300 years, it won’t stay as low as 25 years per generation.

If you have six or more generations in your known lineage, go calculate the average age between generations. If you have enough data, it won’t be 25 years and certainly not 20 years. 33 to 34 years per generation is more accurate.

Ann B.

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I tried to address this topic as it applies to my own family blog/research – see https://nelsonloeb.wordpress.com/the-big-picture/, using this insight about the exponential growth of ancestors to help define the boundaries of my overall research project. I would appreciate any critical feedback about the way I present I the concept. Thanks for your post!

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I’ve noticed in my own family, that my maternal ancestor was the second wife, as perhaps the first wife died in childbirth ( presumptive) but that affects the age question due to the years of remarriage and next-generation birthing. It is somewhat common on my Italian side.

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I use to substitute elementary through high. Sometimes when I was subbing a fifth grade and during the math section of the day, I would drive my students absolutely bonkers telling them they were much more closely related to each other than they could ever imagine – especially if there were various races within the class. I wrote on the chalk board something similar to the chart Richard posted and told them if we could trace a student’s ancestors (I would pick out a white boy, for example) and another student’s ancestors (I would usually pick out a black girl or another boy), we might see they are related to one another – a VERY distant cousin, but still related. This opened up a LOT of discussion and questions of how this could be. It was a lot of fun and a great opportunity to teach kids that race and gender isn’t very important in the grand scheme of things. Just our hometown, for example. When I told them that EACH of us have 2,199,023,255,550 ancestors, I’d ask how could this be? Then, multiply each of us in the classroom – times 30 kids – then the whole school – then all of Rockford, IL (population about 150,000) – then the whole nation and world! Then, I’d ask them how could this be? There would be more ancestors than have ever lived on the planet since the beginning of the earth. They just didn’t get it. So this is when I’d talk and they would ask trying to cope with and understand the sheer magnitude of this simple yet complex fact of existence. A REAL eyeopener for a 10 year old, let alone all of the rest of us!

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There have been a number of recent studies that support the average generation as about 33 to 34 years. You don’t look at it as “how early can a couple conceive a child” and use that number to determine how long a generation is, because “generations” spring from children who were born during the full range of the fertile years of a couple. The average length of a generation should be calculated as the average age of a father when his “middle child” was born. I tested this concept against my own Scottish tree going back to 1685 and it correlated with that concept – it came out as roughly 34 years.

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Its then amazing that anyone could feel lonely.

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