1 in 200 of men alive today are direct descendants of Genghis Khan

Now it comes from a computer model, so there could be errors or exceptions— I'm thinking extant uncontacted peoples, here. The model accounted for this possibility, as the paper notes: ...in order for a remote island to affect the MRCA date, it must have been colonized prior to the lineage of the mainland MRCA reaching the source population and it must have remained genetically isolated until very re- cently in order for there to be surviving people with no modern mainland ancestry.

Remember that uncontacted peoples are uncontacted by us; the ones we know of have regular if infrequent contact with other tribes, so if contacted tribes share the MRCA it's quite probable that uncontacted ones do as well. Could there be a cache of 50-100 human beings somewhere on this planet who happen to share an MRCA with us who is older than the one shared by all other living persons, maybe 10,000 years? Sure. But they would be the only ones out of 7 billion.

[1] http://tedlab.mit.edu/~dr/Papers/Rohde-MRCA-two.pdf

Haven't been able to find it again, though.

"Mr L Prosser was, as they say, only human. In other words he was a carbon-based life form descended from an ape. More specifically he was forty, fat and shabby and worked for the local council. Curiously enough, though he didn't know it, he was also a direct male-line descendant of Genghis Khan, though intervening generations and racial mixing had so juggled his genes that he had no discernible Mongoloid characteristics, and the only vestiges left in Mr L Prosser of his mighty ancestry were a pronounced stoutness about the tum and a predilection for little fur hats.

"...Mr Prosser's mouth opened and closed a couple of times while his mind was for a moment filled with inexplicable but terribly attractive visions of Arthur Dent's house being consumed with fire and Arthur himself running screaming from the blazing ruin with at least three hefty spears protruding from his back. Mr Prosser was often bothered with visions like these and they made him feel very nervous. He stuttered for a moment and then pulled himself together.

"...He saw the bulldozer driver's union representative approaching and let his head sink back and closed his eyes. He was trying to marshal his arguments for proving that he did not now constitute a mental health hazard himself. He was far from certain about this - his mind seemed to be full of noise, horses, smoke, and the stench of blood. This always happened when he felt miserable and put upon, and he had never been able to explain it to himself. In a high dimension of which we know nothing the mighty Khan bellowed with rage, but Mr Prosser only trembled slightly and whimpered. He began to fell little pricks of water behind the eyelids. Bureaucratic cock-ups, angry men lying in the mud, indecipherable strangers handing out inexplicable humiliations and an unidentified army of horsemen laughing at him in his head - what a day."

(Hitchhikers chapter 1)