Race and ethnicity differ from age and sex not merely in degree of mensurability but in kind. For long the dominant impetus from both sides was to foster acculturation, and this peculiar feature was a typical leitmotif of writings on American ethnicity. Censuses taken during the era of the melting pot reflected concern about newcomers' supposed rate of Americanization. Apart from the two anomalies, Indians and blacks, the population was seen as unitary or, at worst, in the process of becoming homogeneous. The expectation that all whites would assimilate into a single new nation was countered by opposition, usually temporary, to the various European nationalities. As cultural pluralism soon supplanted the melting pot as the typical symbol of social policy, the list of acceptable characteristics of the alien stock was repeatedly expanded. Ideally, an enumeration should take place in a political vacuum, for partisan passions about the results typically affect the route to those results.