fast-growing demographic grew by 2.1% analysis of census data grew by 2.1 percent population growth second-largest demographic group www.pewresearch.org population growth grew by 2.1 percent second-largest demographic group www.pewresearch.org grew by 2.1 U.S. births drive grew by 2.1% according to the Pew Research Center www.pewresearch.org grew by 2.1 fast-growing demographic Pew analysis population growth www.pewresearch.org ever-browning America