Even more interesting IMO is that the same argument holds not just for royalty but also for religious figures whose descendants have special divinely-sanctioned

Even more interesting IMO is that the same argument holds not just for royalty but also for religious figures whose descendants have special divinely-sanctioned status in various different religions. For example, it's quite likely that we're all descendants of the original high priest Aaron, whose descendants and no-one else are allowed by God to perform certain actions (caveat: the ancient texts are ambiguous about whether "descendant" means "descendant along both maternal and paternal lines" or whether it's more restrictive, and in certain circles this could be a sensitive question). Similar thing for religious prophecies about peoples' descendants (e.g. that the Messiah is a descendant of Judah---it's probable that we are all descendants of Judah by now).