Multiple Common Ancestors vs. Pedigree Collapse

I recently submitted my renewal portfolio to the Board for Certification of Genealogists for review by the judges in hopes that they would deem my submission worthy of my continuing to receive the credential of Certified Genealogist. This is something I have to do every five years to maintain my credential. I was honored that they said “yes.”

One of the common observations of both of the judges was that I should have used the term “multiple shared lines of ancestry” in lieu of “pedigree collapse.” Now, I had never heard that term, and I set about to figure it out. I thought you might be interested in what I found.

The judge stated, “The explanation might have been clearer if terminology such as “multiple shared lines of ancestry” had been used rather than “pedigree collapse.”[1]

First, I went to the document that included the words pedigree collapse so I could determine the context.
“In order to further reduce the possibility of pedigree collapse creating an inordinately higher concentration of shared DNA than the relationship would justify, the lineage of the remaining families was investigated.”[2]

I decided that I would ask the experts on the Facebook kGroup, “Genealogy tips & Techniques,” one of the wonderful FB sites that provide solid advice. I want to thank the many people who contributed to my learning on this topic.

The easiest way for me to explain their information was:

  • Multiple shared lines of ancestry: are common lineages with others outside your family (in this case the Wood family). This is often discovered when we are doing DNA work as we are working with test takers.
  • Pedigree collapse: is a reduction in the expected number of ancestors within your own family. Think of your fan chart–do you have all unique individuals or do you have some that appear twice? I have two couples that appear twice back about 5 generations, reducing my count of expected great-greats.

This is not an official definition but it appears that the ISOGG Wiki doesn’t have a definition either.[3] None of this should be confused with endogamy (yet I hear that all the time).

We always want to use the right terminology and I agree with the judge on this comment. I should have used the more generic terminology of “multiple shared lines of ancestry.”

I hope this has been helpful.

Happy Hunting!


What I have been doing since the last posting….since it has been so long since I posted… Applied Genealogy Institute is growing appropriately. The practicum-based institute works with a small number of students using an applied learning approach to skills and record sets a genealogist needs. We are getting ready to enroll our next set of students for the fall semester. Pop over to and check out the classes. I am also working on three articles: 1.) responding to peer review comments to a submission of one of my two documents of my renewal to the Q; 2.) gathering information and background about my grandfather, particularly as it relates to his establishment and loss in the 1930s of his private bank; and 3.) identifying 46 orphan train riders that arrived in Hamilton County, Iowa in the fall of 1890. I have found 31 so far.

[1] Board for Certification of Genealogists to Jill Morelli, CG, CGL, letter, 18 June 2022, attachment, Judges’ comments, Judge no. 1, p. 3.
[2] Jill Morelli, CG, “Finding a Father for Marie “Molly” (Fisch/Lancour) Morelli,” work sample 2. This submission was originally published as an article in the National Genealogical Society Quarterly, “DNA Helps Identify “Molly” (Frisch/Lancour) Morelli’s Father”, 106 (December 2018) 293-306. Emphasis by author.
[3] International Society of Genetic Genealogists, Wiki, (


4 comments on “Multiple Common Ancestors vs. Pedigree Collapse

  1. canyongen says:

    Interesting, thanks! When I find these multiple shared lines of Ancestry, I often think “whew! less work!” although I know it can affect DNA research.

  2. Shelby Bender says:

    I agree with the use of multiple shared lines of Ancestry, but at first glance, some may find the terminology to cause more confusion than explanation. Enjoyed your post and certainly want to entertain joining the AGI group when my stormy weather calms down.

    • Jill Morelli says:

      Thanks, Shelby. I agree! Your comment is echo-ed by Blaine Bettinger who said that in their latest DNA class he spent a lot of time explaining the different between endogamy, pedigree collapse and multiple shared lines of ancestry. This was a very basic description. JM

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