Collapsing Pedigrees - Intermarriage of Cousins
Posted to:  Roots_L mailing list
Date:  9 May 1994
From:  Steve Berlin <>
Subject:  In 40 generations we're all cousins?

There is, for me, an astonshing assertion made in a very interesting paper delivered at the World Conference on Records in Salt Lake City in 1980.  In his address, "Connecting Your Pedigree Into Royal, Noble and Medieval Families," Robert C. Gunderson, listed then as a genealogist and Supervisor, Royalty Identification Unit, Genealogical Department, The Church of Jesus Christ of Latter-day Saints, says the following:

"If we were to double the number of our ancestors for each generation until the time of Charlemagne (A.D. 800), we theoretically would have between 4 and 17 billion progenitors in the last generation alone.  Historically, it appears that there has never been, until very recent times, anywhere near this number of people on the en­tire earth at one time, at least since the time of Noah.  This has led to the suggestion that we of European descent are quite probably descended from every couple living in Europe at the time of Charlemagne that has descendants living today."

I have thought about this remarkable statement many times and though I find it intuitively improbable, Gunderson argues that given the likely small population of Europe in Charlemagne's day and through the intervening years that the pedigrees of those of European descent (while he only addresses European descendancy this phenomenon must operate for all peoples) necessarily "collapse" due to numerous cousin intermarriages.  He underlines his point:

"It has been said that if we had the records to develop such a pedigree that we would find Charlemagne on at least one of these lines.  I would be so bold as to suggest that we would probably find him appearing on the pedigree several hundred thousand, even millions of times."

Can anyone support or refute these striking statements?  I knew we are all cousins but I thought we'd need to go back farther than Charlemagne.  The entire paper is fascinating and though it runs to thirteen pages perhaps if there's interest I'll type it up and post it if it is not readily available somewhere.  My copy came from the Family History Library in Salt Lake City.

Steve Berlin
Salt Lake City

Post to:soc.genealogy.misc
Date:19 Nov 1997 20:20:50
Subject:Ancestor Overlap Question

Today I was fooling around with Excel, and decided to see how many grandparents any given person would have after 20, 40, 60 & 80 generations.  By starting with what seemed a reasonable assumption that your ancestors double at each successive generation, I was sort of confused when my calculations showed that the number of g80g-grandparents was a 25 digit number.

It became obvious that my error was to assume that each marriage consisted of totally unrelated individuals.  Each marriage brings together two family trees which must have extensive overlap, or shared ancestors.

Does anyone out there know the statistics involved here.  It would seem that at some point, we hit a ceiling of ancestors that will likely change very little with successive descendant generations. Has anyone out there started to see ancestor overlap?  Or is it something that occurs too far back in time to be noticed?

Post to:soc.genealogy.misc
Date:22 Nov 1997 10:11:50
From:Richard Pence <>
Subject:Ancestor Overlap Question (Shafer) wrote:

It became obvious that my error was to assume that each marriage consisted of totally unrelated individuals.  Each marriage brings together two family trees which must have extensive overlap, or shared ancestors.

Does anyone out there know the statistics involved here.  It would seem that at some point, we hit a ceiling of ancestors that will likely change very little with successive descendant generations.  Has anyone out there started to see ancestor overlap?  Or is it something that occurs too far back in time to be noticed?

This topic has floated around the electronic genealogy world for a good many years and comes up so often that I have saved an exchange that pretty well, at least from a theory standpoint, [describes] the phenomenon of "collapsing pedigrees."

It is this theory the prompts statisticians to say such things as, "if you have any northern European ancestors, the chances are you are not only descended from Charlemagne, but from each of his several wives."

The following also makes the point that all of us have to be related within at least the 50th cousin degree and, for most of us, we are a lot more closely related than that.

This clip was in a message plucked from the Genealogy Conference on the old FidoNet BBS network nearly 3 years ago.  Note that it dates back further than that. The question originally asked was nearly identical to yours.

-----begin old mesage----

How can we possibly have more ancestors in a coexisting generation than the total known population of the earth?

I know for a fact that I have a mother and a father who each has a mother and a father, etc... The direct ancestral chart would look like so:

12 (Mother and father)
24 (grandparents)
38 (greatgrandparents)....

Going backwards it does not take too long to run into a problem.

What am I missing?  Please email your response to me.  Thanks

The only explanation I can offer the original poster is contained in the following article I picked up in one of the genealogy groups some time ago.

Summary of the Shoumatoff article by John Hollenhorst

"The Mountain of Names" by Alex Shoumatoff was published in The New Yorker magazine on May 13, 1985.  Shoumatoff subsequently enlarged the material into a book of the same title.

First, a statistical whopper:  Suppose I calculate the number of ancestors I have, simply by figuring I have two parents, four grandparents, eight great-grandparents, six­teen great-great grandparents, and so on, doubling the number for each generation that I go back in time.  If I take this calculation back to the time of Charlemagne, I would have had 281,000,000,000,000 (that's right, 281 trillion) ancestors, all living at that one moment in history.  Obviously this is impossible.

What prevents this "retrogressive population explosion" from happening?  It's the simple fact that most marriages are between cousins.  Therefore we all share various ances­tors, and my own family tree has far fewer people in it than my calculation would suggest.  This is where a theory called "pedigree collapse" comes into play.

It's estimated that 80 percent of the marriages in world history have been within at least the second-cousin relation­ship.  It's easy to see why.  Most humans have lived in small towns, villages, tribes, close-knit religious communities and so on which encourage marriage within a relatively small universe of possible mates.  Obviously this has been chang­ing a lot in the last couple of hundred years, which should make our gene pool a little healthier in the long run.

The theory of pedigree collapse is that every person's family tree is actually shaped something like a diamond.  If you trace it back a few generations, it gets wider.  But if you keep going back further into the generations, it will even­tually start to narrow and then finally converge to a few ancestors, or perhaps even to a single couple.  (Adam & Eve?)  Shoumatoff mentions a European monarch in the 19th century who illustrates the point.  The European royal fam­ilies are so inter-related that this guy had only 8 great-great grandparents instead of the usual 16!  That's because of cousins marrying cousins.  Individual progenitors occupied more than one place in this King's family tree.  For example, maybe the same guy who was his mother's great-grandfather was also his father's great-grandfather.

Now, the theory of pedigree collapse is that this same phenomenon is true of all our family trees if you go back far enough. The further back you go, the more likely it is that an individual ancestor will occupy more than one spot on your family tree.  So the actual numbers of ancestors at each generational level eventually begins to shrink if you go back far enough.

Demographer Kenneth Wachter once created a proba­bility model for an English child born in 1947.  By tracing back the generations, he would have had 60,000 progeni­tors in approximately 1492.  If you take it back to the time of King John (what's that about 1215 AD?) you would find that 80% of the population of England at that time would be on the family tree of this hypothetical modern-day Englishman.

That means, essentially, that most people born in modern times in England are related to one another, most within a few degrees of cousin-hood.

The British gene pool through those 700 or 800 years also includes people who moved there from the rest of Europe, the Middle East, Asia and so on.  So most people in England today are probably related to almost everyone in all those other places as well.

And, it turns out, the same is true for all of us!

The human species has only been in existence for about 10,000 generations.  The major races (Black, Caucasian, Asian, etc.) only diverged from one another in the last 1,500 generations, at the most.

Shoumatoff quotes science writer Guy Murchie:

Most geneticists agree that "no human... can be less closely related to any other human than approximately 50th cousin, and most of us are a lot closer.  The family trees of all of us, of what­ever origin or trait, must meet and merge into one genetic tree of all humanity by the time they have spread into our ancestors for about 50 generations.

This insight has created a vogue in "horizontal geneal­ogy."  It is fun to discover, for example, that Jimmy Carter and Richard Nixon are 6th cousins.  They share an ancestor named Richard Morris, a Quaker who lived in pre-Revolutionary New Jersey.  Nixon and George Bush are also related:  10th cousin, once removed.

(As a personal aside here, I will note that in Salt Lake City this is a tactic the Mormon Church uses for impressing the dignitaries who visit.  When a President or world leader or some such pays a call on the church leaders, the church will sometimes present the visitor with a genealogy chart to show that he is related to Winston Churchill or Abe Lincoln or Mahatma Ghandi or some such.  If they find axe-murderers on the tree, I suppose they leave that out.)

Guy Murchie, to each and every one of us:  "It is virtu­ally certain that you are a direct descendant of Muhammed... Krishna, Confucius, Abraham, Buddha, Caesar, Ishmael and Judas Iscariot....  The earlier they lived, the more surely you are their descendant."

Shoumatoff:  "The political implications of this great kin­dred are quite exciting.  If all of us could be made aware of our multiple interrelatedness, if the same sort of altruism that usually exists among close kin could prevail through the entire human population... [our] differences... would seem secondary."

It's estimated that about 5 Billion people are alive in modern times.  In the history of the human species about 70 billion to 110 billion of us are believed to have lived at one time or another.

90% of our species passed into oblivion without leaving a record of their names.  Only about 6 or 7 billion left any kind of a paper trail.  Of those, the Mormon Church has records on 1.5 billion!!!!  [NOTE:  This figure is from 1985; presumably there are many more by now. -rp]  Shoumatoff writes, "No genealogical archive is remotely comparable...  It is the closest there will ever be to a catalogue of catalogues for the human race."

"The Mountain of Names" in the title refers to a huge nuke-proof vault full of genealogical records that the Mormon Church maintains in Little Cottonwood Canyon near Salt Lake City.  They use these records to perform temple rituals which amount to the baptizing of dead ancestors.  Don't worry!  They are taking care of all your ancestors too!

John Hollenhorst.


Fascinating stuff!