Andrew McKnight's Ancestories: Coaxing Family Stories Out of the Past

Great question, and the answer is "a lot!" But there are limits, and we've discussed many of them in detail in the past few posts. Here are the highlights - some general conclusions and cautions. There has never been a better time for those interested in their family history to do an autosomal DNA test - the standard offered by all of the popular companies like Ancestry, 23andMe, My Heritage, Family Tree DNA etc. At present more than 20 million people have done so - and that almost certainly includes a lot of people who share some ancestry with you. Add to that the enormous ongoing efforts at digitizing historic records from many countries, and bringing them online along with tools like optical character recognition (OCR) and powerful searching features. It has never before been possible to go so far back into your family's past without leaving your desk! Autosomal DNA (measured in centimorgans , or cM) can provide conclusive evidence about people to whom we are c...

Perhaps by now you have been exploring Ancestry's "shaky leaves", the little icon that serves notice of a Shared Ancestor Hint in the tree of one of your Matches. And how exciting - they too have a John Smith as a 5x great grandfather (5G), and Ancestry says that you are 6th cousins (6C)! Genealogy and genetics are in agreement - huzzah! Well, maybe! The amount of the match is pretty small; clicking on the little i in a dark circle on the match page shows that you match at an amount 8 centiMorgans (cM). Since this is above Ancestry's 6 cM threshold for significant match possibilities, they have showed it to you. But…. Each generation doubles in number, and in theory we'd get equal amounts of DNA from each member of that generation: • 2 parents (50% each) • 4 grandparents (25%) • 8 great grandparents (12.5%) • 16 great-great grandparents 2Gs (6.25%) • 32 3Gs (3.125%) ....and so on. If we go back in time 10 generations, our theoretical tree includes 1,0...