Just to clarify whether or not utilizing a 30 year generation opposed to a 25 year generation would alter the results of TMRCA using a calibrated method, lets review what the difference would be. Using the 25 year generation tied to the mutation rate constant the 111 marker mutation rate constant per haplotype is .198; by the marker, .00178378. The 67 marker constant per haplotype is .12; .001791044 per marker. As related exampled below the conversion for a 30 year generation last year; here is the copy paste from the L21 archives. "On 5/1/2013 5:02 PM, Susan Hedeen wrote: The 111 marker mutation rate constant per haplotype--for 30 year generations is .2376; by the marker would be .0021405. The 67 marker mutation rate constant per haplotype-- for 30 year generations is .144; by the marker it would be .0021492 Susan" Example: From the DS SNP + Haplotypes and TMRCA spread sheet from which David took the "Gs" to example that indeed I was using a 25 year generation that he disagrees with -- 67Marks 54/8/.12=56->60G 1500±260 ybd 450 CE Translation there are 54 infinite allele mutations counted against the group modal for 8 haplotypes divided by the mutation rate constant of .12 per the 67 marker haplotype to arrive at 56.25 generations that is rounded down to 56 and then corrected for back mutations to arrive at 60 Generations. That 60 generations then is multiplied by the statistical generation length of 25 years to arrive at 1500 years; the standard deviation is calculated as 260 years. d=1950 from which 1500 is deducted from to make a mid-line date of 450 CE. So let's look at the difference using a 30 year generation tied to the mutation rate constant. 54/8/.144 = 46.88 rounded up to 47, corrected to 50G then multiplied by the statistical generation length of 30 years to arrive at 1500 years. The standard deviation remains the same and the mid-line date is also the same. This is a calibrated method developed by Anatole A Klyosov and Igor Rozhanski. It has been published along with multiples of papers. This is the primary method that I have been using for the TMRCA for this project. On 5/18/2014 7:25 AM, From Michal Milewski co-admin of the R1a1a Haplogroup project who also does this kind of work and has been working on using SNPs to generate sub-clade ages: "Having two independent (though nearly equally reliable) ways of calculating TMRCAs (using either STRs or SNPs) would be a great thing, as in case of any coincidental aberration related either to significantly skewed SNP rate or to some unusual level of STR homoplasy, the other method will alarm us that something is going wrong (and thus we should apply a much larger margin of error than usually) . Assigning a so-called “basalâ€� haplotype for each node resembles the method used by Klyosov and Rozhanskii, and it should be noted that their STR-based estimates are more or less consistent with the more recent SNP-based estimates..." I hope all who have wondered about this find this example helpful. With best regards, Susan Hedeen