When comparing the general Korean population with a segment of Northern Chinese we see there is a significant disparity in terms of morphological characteristics.
N. Chinese woman
The Mongoloids from China appear to be an ancestral population to the rest of East Asia, but its large territory was a home for a certain variety of phenotypic forms. The general separation is between south/north, and can be divided into directional sections (Northeast, Southwest, ect). If we are able to trace the evolution of these 'phenotypes', we map out an early migration from the south into the north, and later subsequent migration from other parts, most important are those comming up from the coast, then westwards, or those comming from Central Asia/Siberia into north, Tibet , later northeast. The Koreans obviously share things in common with the sorrounding populations, but there appears to have been a large displacement in northern China, which almost completely erased traces of a Western-originating population(s). This group seems to have survived in Japan(Ainu), and possibly other places before Mongoloid population expanded. A subgroup of Koreans seem to have retained some of the non-Mongoloid features of those displaced people. While N. Chinese (Sinic) did not in any significant amount or as much as the Koreans. Later migration from the west (Caucasian people) could have influenced the Chinese and Koreans to about the same amount.