It's clear, that a people directly in the middle of a continent was influenced and is a mixture and symbiosis from all sides. (German nationalists said, a mixtture often of the best, like the French Hugenottin, who were especially skilled and busy craftsmen for instance.) (The nordic ideology was a special case.) It's interesting to see the different influences of thousends of years. But a ethnicity is the result of the product of them. For instance my mother had a French name and an ancestor's - born about 1800 - first and middle name were "Charles Napoleon". Shall I consider myself as French therefore?    
 It's also interesting that a greater part of people with names like Cohn, Cohen, Kohen, said o have its origin in ancient Jewish nobility have a special, seldom genetic commonness, which inherits in the male line or if Einstein had some Sephardic ancestors in Spain several hundred  years ago. But it has nothing to do with the ethnicity.