The longer term downward trend in self-identification as descended from specific European origins probably is correctly explained by generational remoteness from those origins -- as each generation passes, family memories/stories are lost and there is more mixing and dilution of particular origins (speaking as one English-Irish-Scottish-French-German-Luxumburger-American).
A potential explanation for the slight rise between 2000 and 2010 in self-identification of specific European origins is the rise in popularity of genealogy, coupled with the vastly increased internet availability of genealogical records. Many American have only recently re-learned about the origins of many of their ancestors.
A potential explanation for the slight rise between 2000 and 2010 in self-identification of specific European origins is the rise in popularity of genealogy, coupled with the vastly increased internet availability of genealogical records. Many American have only recently re-learned about the origins of many of their ancestors.