In a direct rebuttal to Pastor Rick Warren, author of The Purpose-Driven Life, Tufts philosophy professor Dan Dennet presents the idea of religion as a natural phenomenon -- one that has evolved over millennia to meet humanity's changing needs. While acknowledging that this idea stirs up anxiety, Dennett asserts the importance of studying religions rigorously, even proposing that children be required to study world religions along with reading and math. Dennett, who followed Warren on stage at TED2006, goes on to criticize The Purpose-Driven Life for several claims -- among them a belief that in order to be moral, one must deny evolution.