I remember reading a few reports on how a large number of Chinese have just a few common ancestors a few thousand years ago.
40% of Han have a common ancestor 5000 years ago, though the sample size is still small. Looking forward to new reports as more data is collected.
"But it also points to a more surprising event in China some 5000 years ago in which three populations expanded quickly within 500 years of each other. Each of these populations can be traced to a single man. And yet they now account for more than 40% of today’s Han Chinese population—that’s 300 million living males."
It wouldn't surprise me if many were distantly related, supporting the Shennong (God farmer), Huangdi (Yellow Emperor), Yandi (Flame Emperor) ancestor mythology. The Han however isn't that genetically homogeneous due to intermixing over the years with different tribes and ethnic groups but the relation to each other is still strong. The mythologies revolve around agriculture and taming the rivers, which could explain the population explosion during that time. In other studies 60% of Chinese descended from 5 common ancestors, going back 6000 years.