We often think that everyone in a cluster is related to each through a common ancestor. Our expectation is something like this:

And, we do often see results like this. In this case, the three matches are 2nd cousins (and a 2nd cousin once removed) of the test taker.

Mountains and Valleys

But, what if your cluster includes both 2nd and 3rd cousins? And, what if there were 3rd cousins from your great grandparents’ paternal and maternal sides? You would have a situation similar to this:

In this case, your 2nd cousin would be the “key person” who started the cluster since they likely share more DNA with you than your 3rd cousins. In this example, do all of the matches share a common ancestor? No. Are all of the matches related to each other? No.both  So, why are they in a cluster together?

They cluster because they are all related to you and your 2nd cousin. All of the matches are also related to your ancestral line which includes you, your parent, your grandparent, and your great grandparents shown in the red box.

Though names have been changed, the following is a real cluster comprised of four DNA matches: Don (292 cM), George (183 cM), Sherri (111 cM), and Beth (92 cM).

In this case, you can see that Don, a 2nd cousin once removed of the test taker, had the highest number of centimorgans; he was the key person who started this cluster. And, although he is related to all of the other DNA matches, not all of the DNA matches are related to each other. In this case, Beth is not related to both George and Sherri.

Also, there is not one common ancestor or ancestral couple for this cluster. Instead, we have two overlapping groups with two different common ancestors or ancestral couples. We have the group that shares Polly Randolph as a common ancestor, and we have the group that shares Henry Bennett and Elizabeth Bookout as a common ancestor. These two overlap at the intersection of J. R. Cox and E. Bennett. This type of cluster can be described as mountains and a valley. Polly is at the top of one mountain, Henry and Elizabeth are at the top of the other mountain, and J. R. and E. are at the top of the valley.

While the matches in this cluster do not all share a common ancestor and are not all related to everyone else in the cluster, this cluster is a powerful tool. We can use clusters like these to help us organize our matches, identify unknown matches, and build out our family trees.

Your Turn

How do the members of your clusters fit together? I’d love to see more examples! You can leave a comment, email me at leeds_dana@yahoo.com, or share with me (Dana Stewart Leeds) on Facebook.