Given the considerable mixing of the various ethnic groups in the US and elsewhere it would be very surprising to find anyone who is racially "pure." Jews for, example, have been mixing with the Cristian population for centuries, partly to escape persecution. Prime Minister Benjamin Disraeli of Britain, was born a Jew, but his father had him baptized a Christian so that he could enjoy full citizenship.
Similarly, following the US Civil War, many light-skinned African Americas blended in with the White population. As a result many supposedly White Americans have African blood. As for the numerous other ethnic groups in Europe, the USA, and Canada, many changed their original names to make fitting into their new homes easier, and then later their offspring married into the mainstream population.
