An obvious consequence of a rise in multiracial marriages would be an increase in multiracial children, which would lead to a greater share of the population claiming a mix of racial backgrounds. The marriage of individuals from various European immigrant backgrounds led to the melting pot that characterizes much of today’s white population. It would seem only natural to anticipate a similar boom of multiracial persons in the years ahead. Yet in the case of multiracial marriages, national and cultural boundaries are not the only lines being crossed. New ground is being broken, pushing back against long-standing social and even legal constraints that often subjugated multiracial persons—particularly those with white-black ancestry—to second-class status. In many cases, individuals who could “pass” as white tried to do so in order to become part of the mainstream.

The practice of dividing whites from blacks and other nonwhites began in the early years of nationhood, when the slave population was counted separately and the “one drop” rule stipulated that if a person had any black ancestors, they could not be classified as white. Although classifications in later censuses included Chinese, Japanese, Filipino, and Hindu, there was little attempt to think of these largely “racial” categories as subject to mixing. This stands in contrast to the collection of information on parental birthplace and ancestry or national origin, which was widely used to study the blending of white ethnic populations. Although multiracial populations emanating from multiracial marriages certainly existed, they were not well documented in national statistics…

But the more vivid evidence of the erosion of the white-black divide is found in the South, the region historically most resistant to racial change. Because of past prejudices and customs, the white-black population, as a percentage of all blacks, is still considerably lower in the South than in other parts of the country. In a slew of states from Maryland to Texas, “white and black” populations amount to less than 5 percent of the black-only populations; in Mississippi and Louisiana, “white and black” populations constitute only 1 percent. Yet the South is attracting blacks in large numbers, including multiracial blacks, from all parts of the country. And when states are ranked by the growth in their “white-black” multiracial populations in the first decade of the 2000s, rather than their current totals, the southern states lead all others