Visualizing Clusters with 2nd and 3rd Cousins

When creating a Leeds Method color cluster chart with a spreadsheet or a related, automated tool, I suggest starting with your 2nd and 3rd cousins. For many of us, we can safely use matches 400 and 90 cM. But, why 2nd and 3rd cousins?

If we sort our matches based on our 1st cousins, they would sort into two groups: maternal and paternal. But, if we sort our matches based on our 2nd cousins, they could sort into four groups. To fill in some of the gaps, we also include 3rd cousins.

In doing these sorts, we often create 4 clusters based on 4 grandparent lines.

Four Clusters

My dad has plenty of 2nd and 3rd cousins in the 400 to 90 cM range, so I often use his matches as an example. In my latest AutoCluster analysis report, he got 5 clusters instead of 4. But, there is “heavy overlap” – lots of grey cells – between the red and purple clusters. So, those two can be combined. As you can see by the black outlines that I added, we can now see 4 clusters.

Diagramming Clusters

Lately, I’ve written several posts about diagramming the clusters created from the Leeds Method or any of the automated tools based on this method. In this post, I am diagramming my dad’s 4 clusters. For privacy, I’ve removed names and instead am using a letter and number to indicate each person. The numbers are just the people in a particular cluster in the order they appear. The letters are for the 5 colors in the order they appear:

• • A = Orange
  • B = Green
  • C = Red
  • D = Purple
  • E = Brown

[Note: These diagrams were created with LucidChart.]

The Orange Cluster

The Orange Cluster is made up of two 2nd cousins and one 2nd cousin once removed. Second cousins share a set of great grandparents, in this case, Augustus L. Merrill and Sarah Jane Eastwood.

The Green Cluster

The Green Cluster is a little more complicated. B2 is my dad’s 2nd cousin once removed. They share my dad’s great grandparents, Alexander Stewart and Catharine Jane McClintock. B1 is my dad’s 2nd cousins once removed, but my dad is the younger, “removed” cousin in this case. They share B1’s great grandparents, but this couple is my dad’s great, great grandparents: John McClintock and July Close.

Red and Purple Clusters

As you can see, the Red and Purple Clusters fit together nicely. Several of the matches – C1, C2, C12, C6, and C7 – are my dad’s 2nd cousins (and 2C 1R and 2C 2R). They all descend from my dad’s great grandparents: Carl Peters and Guntherine Werther. But other matches share my dad’s great, great grandparents in common: Guntherine’s parents, Gunther Werther and Molly Reinhardt. These matches are my dad’s 3rd cousins.

Brown Cluster

The Brown Cluster also includes some 2nd cousins sharing my dad’s great grandparents, Josiah Randolph Coppenbarger and Elizabeth Bennett. But, it also includes some 3rd cousins who are descendants of my dad’s great, great grandparents, Elizabeth Bennett’s parents, Henry Bennett and Ellender Bookout.

Four Sets of Great Grandparents

From these diagrams, we can see the “four grandparent lines” that I have often mentioned. These matches are NOT descended from our grandparents; if they descended from our grandparents they would be closer than 2nd cousins. Instead, they descend from the parents or great grandparents of our four grandparents.

Above is an Ancestry.com chart showing my dad’s parents, 4 grandparents, 8 great grandparents, and 16 great, great grandparents. Each cluster represents descendants of one of these pairs of 8 great grandparents OR descendants of a pair of great, great grandparents:

• • Green Cluster: Alexander Stewart and Catherine Jane McClintock or John McClintock and July Close
  • Orange Cluster: Augustus L. Merrill and Sarah Jane Eastwood
  • Red and Purple Cluster: Carl Peters and Guntherine Werther or Johann Gunther Werther and Molly Reinhardt
  • Brown Cluster: Josiah Randolph Coppenbarger and Elizabeth Bennett or Henry Bennett and Ellender Bookout

Conclusion

When we create clusters based on the suggested Leeds Method range of 400 down to 90 cM, we often end up with four clusters. Those four clusters likely represent our four grandparent lines. These 2nd and 3rd cousins are descendants of either our great grandparents or our great, great grandparents. But, each cluster should group around a common ancestor or ancestral couple.

I hope seeing examples of some of the diagrams of these clusters helps you to understand clustering better and to know what to expect from your own clusters.