Principal components (PCs) were calculated based on gene frequencies of 130
alleles at 38 loci in Chinese populations, and geographic PC maps were con
structed. The first PC map of the Han shows the genetic difference between
Southern and Northern Mongoloids, while the second PC indicates the gene fl
ow between Caucasoid and Mongoloids. The first PC map of the Chinese ethnic
minorities is similar to that of the second PC map of the Han, while their
second PC map is similar to the first PC map of the Han. When calculating
PC with the gene frequency data from both the Han and ethnic minorities, th
e first and second PC maps most resemble those of the ethnic minorities alo
ne. The third and fourth PC maps of Chinese populations may reflect histori
cal events that allowed the expansion of the populations in the highly civi
lized regions. A clear-cut boundary between Southern and Northern Mongoloid
s in the synthetic map of the Chinese populations was observed in the zone
of the Yangtze River. We suggest that the ancestors of Southern and Norther
n Mongoloids had already separated before reaching Asia. The ancestors of t
he Southern Mongoloids may result from the initial expansion from Africa or
the Middle East, via the south coast of Asia, toward Southeast Asia, and u
ltimately South China. Upon reaching the Yangtze River, they might even hav
e crossed the river to occupy the nearby regions for a period of time. The
ancestors of the Northern Mongoloids probably expanded from Africa via the
Northern Pamirs, first went eastward, then towards the south to reach the Y
angtze River. The expansion of the Northern Mongoloids toward the south of
the Yangtze River happened only in the last 2 or 3 thousand years.