A large body of research shows that Millennials are significantly less religious than previous generations of young Americans. But as to whether the lack of religion seen in today's Gen Y'ers (born between 1980 and the mid-1990's) is transient or lasting, scientists aren't sure. But now a new review of surveys of more than 11 million adolescents, conducted over the course of almost 50 years, suggests that the religion divide between Millennials and their predecessors is a true generational one.