Two-rooted lower canines are rare in humans, but they are most commonly found among Europeans, at levels of up to 9%. A new study reveals that this trait reached unusually high frequencies in ancient groups from East Central and East Asia, particularly those of Afanasevo, Scythian, Uighur and Ordos origin (2.8% to 4%). This is a strong indication that such groups carried significant European ancestry, and were possibly the descendants of the same European migrants who took R1a1a and Indo-European culture deep into Asia after the Neolithic (see here and here).
In Table 1, the population variation of two-rooted lower canines is shown for major populations of the world. To emphasize the point that this is a European trait, of the 12,128 individuals included in the table, only 306 express two-rooted lower canines (2.5%) but of these 83% (254) were Europeans. If you include related Asiatic Indian, Middle Eastern, and North African populations, this number increases to 89% (272/306).
The presence of the two-rooted canines in East Asia may provide some clue as to the eastward migration of new populations into China and Mongolia. The largest numbers of individuals with this trait are concentrated along the western and northern frontiers of China and Mongolia. Archaeological excavations support the large scale movement of people into this area during the Bronze age (ca. 2200 BCE–400 BCE). Burial artifacts and settlement patterns suggest cultural and technological ties to the Afanasevo culture in Siberia, which in turn is linked archaeologically, linguistically, and genetically with the Indo-European Tocharian populations that appear to have migrated to the Tarim Basin ca. 4,000 years ago (Ma and Sun, 1992; Ma and Wang, 1992; Mallory and Mair, 2000; Romgard, 2008; Keyser et al., 2009; Li et al., 2010).
Christine Lee and G. Richard Scott, Brief Communication: Two-Rooted Lower Canines - A European Trait and Sensitive Indicator of Admixture Across Eurasia, American Journal of Physical Anthropology (2011), DOI: 10.1002/ajpa.21585