Thank god for steppe hyper-patriarchy; it's a model which we can test. Dienekes points me to a paper, The Y-chromosome C3* star-cluster attributed to Genghis Khan's descendants is present at high frequency in the Kerey clan from Kazakhstan, which is notable for increasing sample coverage of the distribution of "Genghis Khan haplotype." As you might recall in 2003 a paper reported that a particular Y-chromosomal phylogeny was extremely common in Central Eurasia, and, that it had expanded rather rapidly starting approximately ~1,000 years ago. The natural supposition was that this was connected to the rise of Genghis Khan, from whom male-line descent in particular has become a matter of pride and prestige across the former domains under his rule. Subsequent researchers have supported this finding insofar as the distribution of the haplotype does tend to drop off among the "Western Mongols," who were for various reasons marginal during the time of Genghis Khan, and whose ruling class were subsequently diminished in part due to their lack of a Genghiside pedigree. The new paper above presents the novel result that the Kereys of Kazakhstan have the highest fraction of C3* reported to date. This elite lineage claims descent from the Kerait tribe of 13th century Mongolia, which was by an large absorbed by the Mongols. The authors suggest that either the C3* star-shaped phylogeny is is actually a Kerait derived line, which piggy-backed on the rise of the Mongol Empire, or, that Keraits and Mongols share a common blood ancestry. In particular, they point out that the Khan of the Keraits, who was for a time the patron of the young Temujin (later Genghis Khan), was also the "blood brother" of Temujin's father. Though this relationship was formed between notional non-relatives, it does not seem implausible that the Kerait and Mongol ruling dynasties were two branches of a common lineage. In particular, the Mongol elite may have been derived from the Keraits as a junior or cadet branch, as the former were relatively marginal at this period in relation to the Keraits, who as Christians of the Church of Persia (also known as 'Nestorian' in the West) were well integrated into the broader Eurasian ecumene. Of course another possibility is that cuckoldry of non-Genghiside lineages was rather common in the early years of the Mongol Empire by Genghiside princes, of whom there were legion, legitimate and illegitimate. Or, perhaps the Mongol ruling clan was cuckolded by the Kerait elite before the time of Genghis Khan. They were after all likely in a position of greater power and prestige. The social science suggests that high status male lineages can rely upon relatively high fidelity of their partners. Additionally, in terms of reproductive value it is likely that in a pre-modern world elite lineages were far more prolific than the masses. The expansion of the Genghis Khan haplotype may be due to direct slaughter of enemies and acquisition of their wives, but what if it is also through less 'honorable' means? That is, not only were the Genghisides prolific in their own right, but they took upon themselves the reproductive rights of other elite men. This model is interesting as far as it goes, but the key question as Y-chromosomal databases expand is what patterns we will see beginning to emerge the world over. Are most of today's men descended from elite lineages, or the bastards of elite lineages, or cuckoldry? A very particular Y-chromosomal distribution of lineages would then manifest itself.