How Many Ancestors?
by
Roger Lawrence

This article was first published in the American-Canadian Genealogist, PO Box 6478, Manchester, NH 03108; and is used by permission of the Editor.

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Since our ancestry comes from a smaller world population than presently exists, just how many ancestors did we have about the year 1000 AD? With each generation, the number of ancestors doubles. for one person, there are two parents, four grandparents, eight great grandparents. Then the number doubles for each previous generation to 16, 32, 64, 128, 256, 512 and there would be 1024 persons in the tenth generation away from us. If the doubling continues, we would have 1024 x 1024 or 1,048,576 ancestors by the 20th generation, and 1,073,741,824 by the 30th generation. At this point, assuming that there is about one generation every 30 years, then 30 generations would equal 900 years, meaning that the 30th generation of over one billion ancestors was living about the year 1100.

The fallacy of this doubling is that we have some ancestors who appear several places in our ancestral "fan Chart". We experience this even in a ten-generation fan chart due to marriages of close and distant cousins. This would be even more so in thirty generations. However, about thirty generations ago, the population of the land which came to be know as France was only about two million people.

A mathematical model was calculated for a more likely number of ancestors based on the principle that some ancestors are duplicated in different lines. Kenneth WACHTER published an interesting mathematical article called "Ancestors at ther Norman Conquest", in Genealogical Demography published by academic Press in 1980. The ancestors were the early Normans and Britons in England by 1066, and the Norman Conquest, but we can apply this equally to any geographic area and nationality.

Using a complex mathematical formula, WACHTER showed that we would have about 97% distinct ancestors and a bit more than 3% duplicate ancestors at the 13th generation, that is about the year 1600. There would be over 625,000 distinct ancestors at the 20th generation so that the remaining third would be duplicate people. The mathematical calculations shows that we would have the maximum number of about 2,042,455 distinct ancestors by about the 24th generation, making up only 11% distinct and 89% duplicate. By the 30th generation, we would have about 952,279 distinct ancestors, so that out of a population of about 1,110,000, about 86% would be our ancestors.

These figures are based on the population of England at the Norman conquest in 1066. But using the same for France, it is obvious that we would not have all individuals in France as our ancestors. Of the existing population, our ancestors would have constituted about 86% of the population. That is about five-sixths of the population of the area of the land referred to as modern France. Less than 14% of the persons at that time would not be related to us. Each of our average since only 8.9% would be distinct.

In earlier generations, there would be still about 85% of the pool of persons as distinct ancestors. Some of us would have ancestors from a greater geographic area than only France and hence probably more actual ancestors if we had them from all of Europe, Then earlier still fewer distinct ancestors before that as we had 85% of a smaller earlier population.

It would appear that whether we can prove it or not, some of our ancestors probably would have been of noble or royal status.

Last Updated: 02/08/2008
Created and Maintained by Larry Warren.
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