Russian ‘ethnicity,’ understood as indicated above, was finally formed approxima

—Russian ‘ethnicity,’ understood as indicated above, was finally formed approximately in the 14th-16th centuries within the central-eastern and northern parts of the eastern Europe, whereas the south and the west of this large area became homelands of linguistically closely related Ukrainians and Belorussians.—

Russians interbred heavily with Finnic Peoples

—“The Y-DNA haplogroup I is found … (23.5%) when the scope is limited to central and southern Russia. Some members of the “Russia-Slavic DNA Project” carry the sub-types I2a and I2a2.”—

The mystery (to me) is what was going on before 700ad?