Traditionally, the time to the Most Recent Common Ancestor (the "MRCA") shared by men belonging to a Y-DNA cluster has been calculated by reference to the number of Short Tandem Repeat ("STR") mutations that are present in the cluster. More recently, Single Nucleotide Polymorphisms ("SNPs") have been used to calculate the time to the MRCA of men belonging to a Y-DNA cluster.
As shown below, use of these methodologies can yield varying results, depending upon, among other things, the mutation rates that are used and the pool of men for whom test results have been received. STR-based analyses have suggested a time to an MRCA for R1a1a Ashkenazi Levites of about 800 to 1,500 years; SNP-based analyses have suggested a time to an MRCA for R1a1a Ashkenazi Levites of about 1,500 to 2,500 years.
Note that the time to an MRCA should be adjusted by taking into account the average age of men who have done Y-DNA testing. Doing so will add about 50 years to the time to an MRCA.
Calculation of Time to an MRCA Based Upon STRs
By considering the number of STR mutations that are present in a Y-DNA cluster, the number of STR markers tested, and the mutation rates of STR markers, it is possible to calculate how long ago the MRCA of the tested men lived.
The accuracy of such calculations will depend in large part upon whether the test results are from a representative group of men. Furthermore, to the extent that a cluster includes a large group of men who share a relatively recent MRCA and only a small group of men with a more distant MRCA, calculations will underestimate the time to the cluster's MRCA.
Third-Party Calculations of Time to an MRCA Based Upon STRs
According to a 2012 article by Rozhanskii & Klyosov on the R1a haplogroup, the “large Jewish R1a1a-L342.2 branch” “descends from a common ancestor who lived only 1300 ± 150 ybp [years before present].” I. Rozhanskii & A. Klyosov, Haplogroup R1a, Its Subclades and Branches in Europe during the Last 9,000 Years, Advances in Anthropology, Vol. 2, No. 139-56 (2012).
In an April 2014 article posted here, Klyosov calculates, based upon the same methodology and a set of 179 67-marker haplotypes for R1a1a Ashkenazi Levites, that the MRCA for R1a1a Ashkenazi Levites lived 1,250 years ± 130 years ago. In the same article, using a spreadsheet that calculates time to an MRCA based upon marker-specific mutation rates, Klyosov calculates a time to an MRCA of 1,123 years ± 168 years ago. As Klyosov notes, both time frames are consistent with that calculated by Rozhanskii and Klyosov in their 2012 article, based upon a smaller number of haplotypes.
Palisto, who runs the Kurdish DNA website, has calculated a time to an MRCA for R1a1a Ashkenazi Levites of 950 years (and a time to an MRCA for Z2122+ men of 2,457 years).
Calculations of Time to an MRCA Based Upon STRs Compiled for This Website
As noted above, the accuracy of the calculation of time to an MRCA will depend in large part upon the representativeness of the sample of the men whose test results are considered.
The group of R1a1a Ashkenazi Levite men who have tested to 111 markers appears to be more closely related than the group of men who have tested to 67 markers (perhaps because men with close matches at 67 markers are more likely to have upgraded their test results to 111 markers than are men without close matches).
As a result, a time to the MRCA for R1a1a Ashkenazi Levites calculated based upon test results at 67 markers is more likely to be accurate than one based upon test results at 111 markers; conversely, a time to the MRCA for R1a1a Ashkenazi Levites calculated based solely upon test results at 111 markers is likely to understate the time to an MRCA. Accordingly, this website calculates the time to an MRCA based upon results at 67 markers.
For men whose results are posted on this website and who have tested to at least 67 markers: (1) using a Janzen spreadsheet, the time to an MRCA for R1a1a Ashkenazi Levites is about 910 years; and (2) under Anatole Klyosov's methodology, the time to an MRCA for R1a1a Ashkenazi Levites is about 1,165 years, plus or minus about 120 years. (The slight discrepancy between this figure and the figure of 1,250 years ± 130 years ago calculated in Klyosov's April 2014 article presumably reflects the fact that this website has compiled a substantial number of STR test results that are not posted on FTDNA project pages and therefore were not considered by Klyosov in his calculations.
For men whose results are posted on this website and who have tested to at least 37 markers, (1) the Janzen spreadsheet calculates a somewhat higher time to an MRCA for R1a1a Ashkenazi Levites of about 1,080 years; and (2) under Anatole Klyosov's methodology, the time to an MRCA for R1a1a Ashkenazi Levites is about 1,180 years, plus or minus about 120 years.
Sidney Sachs, project administrator of the Y-Haplogroup J2b_445-8 Project, calculates about 800 years (28 generations at 28.8 years/generation) to an MRCA based upon the 37-marker results reported on this website as of December 20, 2013, using the rates that Dr. John Chandler reported in J. Chandler, Estimating Per-Locus Mutation Rates, Journal of Genetic Genealogy 2:27-33, 2006 as applied to a genetic distance of 326 steps over 1,388 marker values at 37 markers (yielding a mean value of 4.26 (1388/326)). Using the same methodology, Sachs calculates about 835 years (29 generations at 28.8 years/generation) to an MRCA based upon the 67-marker results reported on this website as of December 20, 2013, also using the rates reported by Chandler.
William E. Howard III calculates about 1,180 years (42.2 generations at 28.8 years/generation) based upon 37-marker results for the R1a1a Ashkenazi Levite men whose test results were reported on this website as of December 20, 2013, using the methodology described in W. Howard, The Use of Correlation Techniques for the Analysis of Pairs of Y-STR Haplotypes, Part I: Rationale, Methodology, and Time Scales, Journal of Genetic Genealogy, 5(2) : 256-270, 2009, and The Use of Correlation Techniques for the Analysis of Pairs of Y-STR Haplotypes, Part II: Application to Surnames and Other Haplotype Clusters, Journal of Genetic Genealogy, 5(2): 271-288, 2009.
Wim Penninx, in his calculation of time to an MRCA for Y-DNA branches of Ashkenazi Jews, estimates that the MRCA for R1a1a Ashkenazi Levites lived in about 752 to 900 CE, based upon his analysis of 192 R1a1a Ashkenazi Levites at 67 markers. For this website, he has calculated that: (1) the MRCA for Y2619+ Y2630+ R1a1a Ashkenazi Levites lived in about 950 to 1120 CE; and (2) the MRCA for Y2619+ Y2630- R1a1a Ashkenazi Levites lived in about 650 to 885 CE. He has also calculated the time to an MRCA for three separate clusters of Y2619+ Y2630- R1a1a Ashkenazi Levites identified elsewhere on this website: (1) the MRCA for Y2619* Tentative Cluster A lived in about 740 to 1192 CE; (2) the MRCA for Y2619* Tentative Cluster B lived in about 892 to 1169 CE; and (3) the MRCA for Y2619* Tentative Cluster C lived in about 920 to 1560 CE (the broader time range for this cluster reflects the small sample size).
Calculation of Time to an MRCA Based upon SNPs
In their 2013 paper analyzing the SNPs of R1a1a Ashkenazi Levites, Rootsi & Behar state that "the tight cluster of Askhkenazi Levite R1a-M582 haplotypes strongly indicates a recent origin from a single common ancestor who, according to our provisional dating, lived" about 1,500 to 2,500 years ago.
As discussed in more detail here, Michał Milewski has estimated that the R1a1a Ashkenazi Levite common ancestor lived about 1,500 to 1,700 years ago, based upon the initial results of full Y-DNA testing through Full Genomes Corporation and Family Tree DNA's Big Y test and analyses of R1a1a Ashkenazi Levites whose Y-DNA was sequenced as part of scientific research.
There is a fairly strong possibility that as more R1a1a Ashkenazi Levites do full Y-DNA sequencing, we will find some Ashkenazi men with a family tradition of Levite descent whose R1a1a lines branched off sometime before the MRCA shared by most R1a1a Ashkenazi Levites. The most likely candidates are men who are quite far from the mode and who have the STRs DYS537=11and DYS650<20 - the STR marker values that are shared by the R1a1a Ashkenazi Levites with the greatest genetic distance from one another, indicating that those STR marker values were likely those of their distant MRCA.
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