Interracial marriages in the U.S. have climbed to 4.8 million - a record 1 in 12 - as a steady flow of new Asian and Hispanic immigrants expands the pool of prospective spouses. Blacks are now substantially more likely to marry whites.A Pew Research Center study, released Thursday, details an America where interracial unions and mixed-race children are challenging typical notions of race."The rise in interracial marriage indicates that race relations have improved over the past quarter-century,” said Daniel Lichter, a sociology professor at Cornell University. "Mixed-race children have blurred America’s color line. They often interact with others on either side of the racial divide and frequently serve as brokers between friends and family members of different racial backgrounds.”In all, more than 15 percent of new marriages in 2010 were interracial.