In my last post I outlined two insights from analysis of my 8700 Matches at AncestryDNA with confirmed Common Ancestors (CAs): the number of Matches increases dramatically with each generation going back to the 6C level (where ThruLines ferrets out a lot of my cousins); and the average cMs flattens out in the mid-teens beyond the 4C level.

For this post I analyzed the Matches to see the distribution based on shared cMs.

Shown and not shown are 1491 Matches over 20cM, about 17% of the total. But the insight is that 83% of the Matches are from 6 to 20cM. And you can easily see the spike at 9cM. You’ll also notice the Matches at 6 and 7cM which I saved just before the AncestryDNA change in the lower threshold several years ago. I’m not sure there is a drop at 8cM – maybe because I haven’t found a lot of Matches at the 7C level and beyond.

At this point, as a life-long genealogist, I want to reiterate that cousins are where you find them and by far most are under 15cm (what we usually call small segments). And this is just the tip of the iceberg, because most of our true cousins beyond 4C (who have taken a DNA test) do not show up as DNA Matches. Most of my under-15cM Matches are also part of interrelated family groups (per ProTools), and their lines usually agree with standard genealogy research. A small percentage don’t and I remove them from the spreadsheet and this analysis.

Everyone has their own objectives in genetic genealogy. I encourage you to think about yours and write them down. Collecting cousins is not my objective but documenting interrelated cousins in family groups (with ProTools), and building evidence for each Ancestor is. This includes finding a few Ancestors that don’t “look” right and turn out to be NPEs. Or using Triangulated Groups or Clusters or Floating Branches to build evidence to break though Brick Walls/NPEs.

Clearly this is genealogy “big picture”. It forces me to treat all lines and Ancestors equally (yes, after I’ve spent a lot of time on my favorites). However, some of these insights, will also help with “targeted” objectives into specific areas of our genealogy.

[06H] Segment-ology: Insights into Matches; by Jim Bartlett 20260125