
Originally Posted by
Angela
What maps? The Behar et al PCA that I posted? That shows how Jewish geneomes plot in relationship to each other and to European and Near Eastern populations, as I'm sure you know, so I guess that was a rhetorical question? :)
Different tools tell us different things. Some tools are terrible for the purpose of discovering Ashkenazi ancestry in other groups, like the "J" calculator created by Eurogenes. Some are very good, like AC at 23andme, because it's tracking IBD segments.
If that tells you that you have AJ ancestry you have it, in my opinion. If it tells you that you don't, you don't. Tests for precision show 97% accuracy at picking out AJ ancestry. You can see the statistics in their White Paper detailing their methodology. You can even figure out pretty closely when it entered your family tree. Of course, given the algorithm 23andme uses, it can only trace IBD sharing back so far. Research groups like Ralph and Coop could perhaps track it back to 2500 BC.
One way that the accuracy is proven is that when people get that AJ percentage in Ancestry Composition they at the same time get LOTS of distant Askenazi cousins, so many that it can overwhelm the 1000 relative limit and stop you from seeing other kinds of matches. That happened to a woman I know who is only 1/8 Ashkenazi. People have a lot of complaints about that, but it's a function of the fact that so many AJs test. Believe me, there have been plenty of people who, for obvious reasons, didn't want to believe some of these results, but they can't deny all those segments that they share with AJ people. When they re-check their paper trail, they almost inevitably find the "hidden" AJ ancestor, and in the generation predicted. (This can't be done with the Sephardim, by the way.) So, if a Pole tests at 23andme, and it says that Pole is 3% AJ, he or she can take it to the bank, as far as I'm concerned.
I'm sorry, but Elhaik is a crank and a quack whose paper has been totally discredited by subsequent papers. The Khazar Theory is dead. I don't know of any researchers who take it at all seriously any more. Just put his paper into google scholar and check the citations which mention it and you'll find all the papers that tear it to shreds.
Oh, the bottleneck is dated to somewhere around 800 years ago, so around 1200 AD, which is right around the massacres in France and the Rhineland at the time of the Crusades.
There were huge gains in population in Europe in general in the 19th century, due to improved nutrition, but also due to clean drinking water, the construction of sewage systems etc. However, Jewish increases in population were even higher. Somewhere I've seen that there were not only very large families, but their infant mortality rate was lower.
"Jewish populations in Eastern Europe had the highest rate of natural increase of any European population in the nineteenth century, with a natural increase of 120,000 per year in the 1880s and an overall increase within the Russian Empire from one to six million in the course of the nineteenth century."