John Hawks reviews a few recent papers about unique Y-chromosome haplotypes which are very widespread and thus likely reflecting recent historical events. Since the Y-chromosome is passed from father to son, a sufficiently detailed genetic map--a "fingerprint"-- which yields a match between two people means it's very likely that those men got their Y-chromosome from the same male lineage. When this all occurs in the same village that's no big deal; but when it's spread across continents, it suggests some male had a phenomenal number of surviving descendants.
The first case Hawks reviews is an unusual Y-chromosome fingerprint which occurs all the way from the Caspian Sea to the Pacific, inheirited by up about 8% of all males in this vast region, or 0.5% of ALL the males IN THE WORLD. Indirect genetic evidence and historical accounts suggest they are ALL direct male descendants from Ghengis Khan.
The second case is in its own way even more interesting. Many Chinese but hardly any Han (the main ethnic group) have a Y-chromosome fingerprint that may have arisen in the 1500s or so. This appears to be linked to the Manchu conquest of China, in which the Qing dynasty-- a partiarchy of up to 80,000 male descendants of Giocangga (died 1582)-- basically lived off the backs of the Han. Here the history and the genetics are in pretty good register, although the molecular clock method for calculating the age of this unique haplotype gives a very broad range of dates.
Hawks is very good at outlining the imperfect seams between the genetic and the historical data. Together they make a very interesting picture. Genetics in particular can illustrate the tremendous difference in descendants between Ghengis Khan and Farmer Brown.
Update: the Giocangga study got written up in Nature as well.