GROUP 8 NOTES
by David B. Boles
Bowles DNA Project administrator
There appear to be two distinct subgroups within Group 8 that can be contrasted with the remaining kits. One, which I will call the "12" subgroup, is distinguished by a value of 12 for marker 22, and consists of kits #126464, 287032, and 341274. Because the Group 8 standard has a value of 15 for this marker, and there are no intermediate values (i.e., 13 or 14) among the other kits, it seems likely that the change from a value of 15 to 12 occurred through a single mutation event.
The other, which I will call the "17" subgroup, is distinguished by a value of 17 for marker 30. The kits are #57613, 194902, 263785, 308906, and 864348. Four of the five subgroup members have an additional mutation, defined as a value of 11 for marker 26. These circumstances suggest that the "17" mutation occurred first, followed by the "11" mutation in a sub-sub-grouping of members.
The remaining kits appear to have no distinctive characteristics that allow groupings. Although four kits show a value of 35 for marker 34, they include two in the "17" subgroup, and two outside that subgroup. Similarly, seven kits show a value of 39 for marker 35, but they include kits both inside and outside the "12" and "17" subgroups. It seems likely that markers 34 and 35 independently mutated at several different times, reducing their usefulness in defining subgroups.
Although the remaining kits, which I will call the "remainder" group, therefore cannot be said to form a subgroup, they do have an interesting characteristic: They show either equivalent or smaller deviations from the group standard compared to the two subgroups. If confined to ancestors with some form of the surname, and at least 37 markers, they include kits #29401, 106142, 164685, 198726, 355920, 546050, and IN83727. The average deviation from the group standard is 2.0 markers (of 37) for these five kits. That compares to a similar deviation of 2.3 markers for the "12" subgroup, and a larger deviation of 3.8 markers for the "17" subgroup. These numbers suggest that the "17" subgroup split off first from the ancestral lines of all other Group 8 members.
When that split occurred can be estimated. Assuming, based on the above deviations, that the "12" and "remainder" members all split off after the "17" members, the number of markers differing between a "17" member and any other member should be related to the number of generations since the split. Estimates are available by using the calculator at http://dna-project.clan-donald-usa.org/tmrca.htm for tests of 37, 67, and 111 markers. For example, kit #263785 of the "17" subgroup, with 67 markers, and #341274 of the "remainder" group, with 111 markers, are different in 6 out of 67 markers. According to the calculator, this difference translates to an estimated 16 generations since the split, the point at which more generations are just as probable as fewer generations.
For each of the ten members of the "12" and "remainder" groups, a generation estimate may be made for each of five possible pairings with a "17" member. These can then be averaged. For example, kit 341274 is estimated to have diverged from the ancestral lines of kits 57613, 194902, 263785, 308906, and 864348 in 19, 16, 16, 12, and 16 generations respectively, averaging 15.8 generations. Across all ten members of the "12" and "remainder" groups, the overall mean is 16.04 generations, with a standard deviation (a measure of variation around the mean) of 2.14.
Now we come to the payoff from the calculations. The calculator incorporates the assumption that a generation is 31 years. The split of the "17" group from the remaining Group 8 members is therefore estimated to have been 31 X 16.04 = 497 years prior to the average birthyear of the testees. If that is assumed to be 1960 (I think it safe to assume that participants tend to be older than the general population, and some test results are a number of years old), the split of the "17" subgroup is estimated to have occurred in the year 1463. Furthermore, the standard deviation allows the calculation of an "interval of uncertainty" of ± 47 years, with 95% confidence that the actual year falls within that interval, i.e., 1416 – 1510.
Applying similar methodology to other subgroups as well as individuals of particular interest results in the accompanying branching diagram. The main events depicted in the diagram as are follows, all relative to the line leading to the participating descendant of the Earl of Glasgow (kit #355920):
-- "17" subgroup divergence, 1463 ± 47 years
-- "11" divergence within the "17" subgroup, 1542 ± 143 years ago
-- Limavady family divergence, 1573 ± 148 years ago
-- "12" subgroup divergence, 1650 ± 133 years ago
The size of the interval of uncertainty is tied to the number of participants. It is small (± 47 years) in the case of the "17" divergence because there were ten participants in the "12" and "remainder" groups to compare the "17" members to. The other divergences, in contrast, are all based on three or four participants, making for much larger uncertainties (± 133 to 148 years). The key to improving these estimates, of course, is to increase the number of participants. More participants should also allow the identification of other subgroupings in the "remainder" group.
Please keep in mind that these are my personal conclusions only. Please don't attribute them to FTDNA.