Three Families or Three Branches?

Over the past five years as the Slaven DNA Project results have come in, we've speculated whether we may find an individual/family line that would be a "bridge" between Groups A and B. With four differences between the two groups in the standard 25 markers and five in 37, it's obvious that the two lines-- if they descended from a single individual-- branched off from each other several hundred years ago. Yet the two groups share a couple uncommon values, and both are suspected of belonging to the R1b1c7 haplogroup (actually Group B has been tested and found to be R1b1c7). But estimates of the R1b1c7 haplogroup's age range up to and beyond 3400 years, or several thousand years before surnames or clan groups came into existance in Ireland.

If Group A would test out to be R1b1c7, then we know that the two groups are related. The question then is whether that ancestor lived two or three thousand years ago and by chance two different groups not related for dozens of generations adopted our surname, or whether the two lines split in the past several hundred years, after the Sléibhín surname had been adopted.

What would help tip the scale towards the second idea would be finding a family line that "bridges" the two groups. It would be descended from the same founding family line as the other group, so it would have the same values as Groups A and B on most markers. For the five markers where Groups A and B disagree, the bridge line would match Group A on some markers and it would match Group B on the others.

And that's exactly what we have in participant MSCAQJ. On the five markers where Groups A and B deviate in the 30 markers in common between Family Tree DNA and DNA Heritage, he matches Group A on three of the values and Group B on the other two. In addition, he has mutations on two markers where Groups A and B match. This is also what you would expect to see in three branches arising from the same common ancestor hundreds of years ago. Mutations occur randomly across the collection of markers, so if you had three family lines that branched from a common ancestor many generations ago you would expect that all three lines would pick up a similar number of mutations, but the mutations would be distributed across the range of markers.

The table below charts those difference, and infers what the common ancestor had for the marker value by using the value that two of the three lines share.

Participant MSCAQJ has been SNP tested by DNA Heritage and the results point towards his haplogroup also being R1B1c7. DNAH does not test for the M222 mutation that defines R1B1c7, but it tests for the mutations that define several of the other R1B1c* subgroups, and he was negative for those mutations. So although not conclusive, the SNP test strongly hints that he too is R1B1c7, like Group B.

Surnames and clan names developed in Ireland in the 10th and 11th centuries-- or for the math to follow, a thousand years ago. Most scientific studies use 25 years as an average generational length, so there have been approximately 40 generations since the adoption of surnames. Using Ann Turner's Mutation Calendar and plugging in 30 markers, the usual mutation rate of .002 mutations per marker per generation, and 120 transmission events (three family lines of 40 generations each), the expected number of mutations would be 7.2-- and we have seven mutations between the three lines in the 30 markers. So that falls into line with what we're seeing.

Another way of estimating the distance in years/generations between two family lines, based on the number of markers compared and the number of differences, is to calculate the number of generations to the most recent common ancestor (MRCA) based on probability. Using the Moses Walker MRCA Calculator and comparing the the groups to the suspected ancestral values, there is a 50 percent probability that Group A and participant MSCAQJ are 23.2 generations removed from the ancestral values, or about 575 years, and Group B is 32.4 generations (800 years) away from the ancestral values at a 50 percent probability. This strengthens the idea that the three groups could have split off from a common family line after the Sléibhín surname had been adopted.

Since we're talking about possible relatedness in a 600-800 year time frame there's no way that this can ever be proven through traditional genealogy. As anyone who's worked with Irish records knows, it's tough just getting back to the 19th century! But if the Sléibhín surname dates back a thousand years as The Annals of the Four Masters and other old texts state, then there has been plenty of time for multiple lines to have branched off and developed their own distinct group of mutations, as postulated above.

Copyright © 2008 Larry Slavens. All rights reserved.