Take a look at Figure 3 of the M222 paper that John and I wrote. It can be found at: http://mysite.verizon.net/weh8/sitebuildercontent/sitebuilderfiles/M222Paper.pdf I think that the slope can be used to determine the population of Ireland at the time the M222 SNP originated. To do that, we have to make some assumptions - 1) that the slope of the M222 relation that reflects the growth of the M222-carrying population will also be applicable to the growth of population in general. 2) that the slope does not change with time (reasonable because of the constancy of slope in Figure 3). 3) that the RCC time scale can be applied over time scales of 4000 years back in time (there is no reason to believe that it cannot be applied back to Y- Adam) 4) that events in history will affect the total population the same way that it affects the M222 SNP. With those assumptions, we can estimate the total population of Ireland in 1680 BC (the time the SNP originated) if we know the population at the birth-year of the average current testee (about 1945) and the number of testees who carry the SNP. We want to do only a crude, back-of-the-envelope computation and will settle for errors as large as a factor of 10 (an order-of-magnitude calculation). So, the population of Ireland in 1945 is estimated to be about 4.5 million people. The population of M222 was 1 in 1680 BC (from Figure 3). Figure 3 shows that the number of people in 1945 who carry the M222 SNP is probably between 700 and 1000, considering a probable incompleteness factor. (Remember all we want is a ball-park estimate; we don't have to know where they now live!). Now we operate on the first assumption — that the ratio of the current population to the population in 1680 BC will be in the same ratio derived for the M222 SNP carriers. So, the population of Ireland at the time of the M222 SNP's origin was of the order of 4500000/850, or 5000 people. But, this is for the total population in Ireland. The number of males was about half that number, or 2500 people. These people in 1680 BC will probably be located near the seacoast or along the rivers of Ireland because of food, ease of travel and mutual protection. They probably lived in clusters of perhaps 10-30 people. This means about 5000/25 or 20 family clusters. The coastline of Ireland is about 1700 miles long, so -- on average, if they are living only on the coast, each family cluster will be separated by an average of about 1700/20= 85 miles. That separation indicates that the families will probably be independent of each other. To afford protection against marauders, they may cluster in larger family groups, but this will separate the groups even farther. And if they locate themselves inland on rivers we can expand the coastline estimate to include rivers as well, driving up our 1700 mile estimate to perhaps 2300 miles. This serves to further increase the inter-family group distance to 2300/20 ~ 120 miles, further isolating the groups from each other. Many of these family groups will be inquisitive and will be aware of their nearest neighbors, but commerce between them, in this era prior to good ships, will be minimal. In fact, there may be occasional problems with assets like food that may affect one family cluster more than its neighbors and those in need might be tempted to raid nearby family clusters for survival. Hence the need to fortify the family units against their neighbors. I find this flow of thought to be interesting. I would appreciate comments from anyone who reads this list. Remember all these estimates are ball-park only. I may be off by a factor of 10 since it is a back-of-the-envelope calculation, expected to be within that order of magnitude. Its the sort of flow of thought that Enrico Fermi often posed to his friends when they went out to lunch together in Chicago. One of his most famous questions was -- Estimate the number of barbers in Chicago! This is a true, back-of-the-envelope calculation expected to be good only to about an order of magnitude, a factor of 10! Comments anyone? - Bye from Bill Howard PS - If my assumptions are correct, Figure 3 can be used in this way to calculate the origin of other SNPS and to make very crude population estimates.