Pedigree Triangulation: What is it and How Can it Solve Brick Walls?
Have you heard the term “triangulation” applied to using DNA in genealogy and wondered what it meant? Triangulation is such a powerful tool that the major DNA testing companies as well as third party companies are working hard to provide easier ways for using this concept. In this article, I’ll explore pedigree triangulation and show you examples to help you understand what it is and how it can confirm your research and make progress on genealogical challenges.
Two types of triangulation can be used with genetic genealogy: pedigree triangulation and segment triangulation. We’ll discuss pedigree triangulation in this article and tackle segment triangulation next.
What is Pedigree Triangulation
What exactly is triangulation? Wikipedia explains it as “the process of determining the location of a point by forming triangles to it from known points.” (1) Triangulation has been used for centuries in science, mathematics, technology, and even psychology. For example, in Air Force survival training, a method of triangulation is used to help a downed pilot figure out where he/she is located.
When was triangulation first used with genetic genealogy? When consumer DNA testing first began, genetic genealogists spoke only of segment triangulation. With additional tools developed by the DNA testing companies and third party companies, pedigree triangulation has become a valid methodology to work with our DNA test results.
The visual below courtesy of the ISOGG Wiki page helps to understand the concept. The bottom leg of the triangle represents a DNA match between Persons A and B. Both inherited a piece of DNA from a common ancestor. The other two legs represent the pedigree lines back to that ancestor. Depending on how close the DNA match, the lines back may be only a generation or two, or they could stretch back several generations to the MRCA (Most Recent Common Ancestor).
How to Use Pedigree Triangulation
The key concept with pedigree triangulation is determining a group of people sharing DNA from a common ancestor. This group is called a genetic network. Key to the process is verifying the generational links tying yourself and your DNA match back to that common ancestor.
The original method involves comparing the family trees of people in your match list. Then “shared matches” or “in common with” are used to separate people into familial groups that are maternal vs. paternal, and maternal grandfather vs. maternal grandmother, etc.
Sometimes you have to build a family tree for someone on your DNA match list. Ancestry and My Heritage both have hints to help build trees and you can compare records to ensure that you are accurately linking one generation to the next. Once you identify where your tree intersects with someone on your DNA match’s tree, you can focus in on identifying the exact common ancestor.
This method takes into account the fact that you both have DNA that matches exactly on the same chromosome(s) in the same location(s). But with pedigree triangulation you don’t necessarily have to look at the chromosome level to determine that you and a match have common ancestors.
How do we create genetic networks from our thousands of DNA matches? We can do this manually using the DNA testing company tools like Shared Matches and In Common With (ICW) filters or the Leeds method. Additionally the testing companies and others have developed automated tools for grouping our DNA matches into genetic networks. For more information on these methods see Robin’s post “10 Ways to Group Your DNA Matches into Genetic Networks.”
Recently Ancestry and My Heritage have introduced exciting tools to help us get started with discovering common ancestors. We need to understand the limitations of these and how they can be a springboard to our research.
I’ll illustrate using my recent research project of proving the hypothesized relationship of Rachel Cox to father Benjamin Cox. My objective gives more details. (See additional articles on this research project at the end).
The objective of this research project is to test the hypothesis that Benjamin Cox was the biological father of Rachel Cox through DNA evidence and traditional genealogy research. Benjamin Cox was born about 1791 in Ohio and died between 1870 and 1880 in Bell County, Texas. Rachel Cox was born about 1828 in Indiana and died between 1870 and 1880 in Falls County, Texas. Rachel married Hickman Monroe Shults on 4 July 1848 in Navarro County, Texas.
Ancestry DNA – Thrulines
When Ancestry DNA rolled out Thrulines, I explored the various ancestors suggested for me and was excited to see Benjamin Cox among them. I had added Benjamin to my Ancestry tree in hopes of discovering possible DNA matches through him. With thousands of DNA matches and the possibility that any matches would be buried among those thousands, I was stymied. Benjamin Cox would be my 5th great grandfather and any DNA I inherited from him would likely be a small segment and show up towards the end of my match list.
How did ThruLines help? Ancestry’s technology searched user-created trees to find my DNA matches that also had a connection to Benjamin Cox. Currently I have 66 DNA matches. The number can change depending on new matches or trees being added or deleted. What does this tell me? I’m on the right track with my research. To check the accuracy of ThruLines, I looked at the suggested matches that I might know – those through my great grandfather, William H. Shults.
The image below shows the connections ThruLines built for me back to Benjamin Cox. My two closest cousins descending through Lola and Dora Shults I have contacted and know are my cousins. Interesting is the new match through Dora C.B. Although the name is written differently, Dora C. Shults and Dora C. B. are the same person, my great aunt.
I recognized the surname of this new match and surmised she was the grand-daughter of my closest match. The 34cM we share is on the low end of a 2nd cousin 1 removed, but it works.
ThruLines showed correct relationships I had confirmed both with a paper trail and contacting my genetic cousins – pedigree triangulation. Each of my matches could be placed at the bottom of the triangle and our lines traced back to William H. Shults, our MRCA at the top of the triangle.
Would pedigree triangulation work for more distant matches such as those showing on Thrulines for Benjamin Cox? Currently six children for Benjamin Cox are shown and 66 DNA matches to his possible descendants. The image below shows my 3rd great-grandmother, Rachel Cox, and three of the five potential siblings.
For each DNA match I’ll need to confirm the paper trail back to Benjamin Cox. The more of these DNA cousins I can confirm, the stronger my proof that Benjamin Cox is our MRCA and indeed the father of my Rachel Cox.
My Heritage – Theory of Family Relativity
Another exciting new tool developed by My Heritage is the Theory of Family Relativity. Based on user submitted family trees, the technology will suggest the MRCA (most recent common ancestor) and show a proposed line back to that ancestor from both you and your DNA match. I currently have 44 suggestions and doing a surname search for “Shults” I discovered an interesting match through Rachel Cox and Hickman Monroe Shults.
My DNA match descends through John Monroe Shults, a younger brother of my William Henderson Shults. I worked with another researcher several years ago and confirmed this line through documentary research. Having that research confirmed through DNA is gratifying.
With DNA technology rapidly moving forward, we can expect improvements with all the DNA testing company and third party tools. What do we need to do? Continue to research our family lines. The more complete our family trees, the better we’ll be able to connect with our DNA cousin matches using pedigree triangulation. We’ll be able to confirm our hypothesized common ancestors and discover new ancestors to research. The sky is the limit and the future is bright.
Best of luck in all of your genealogical endeavors!
Follow my DNA research project: Determining a Father for Rachel Cox
(1) Wikipedia contributors, “Triangulation (disambiguation),” Wikipedia, The Free Encyclopedia, (https://en.wikipedia.org/wiki/Triangulation_(disambiguation) : accessed 23 July 2019).