Almost half of the US public rejects the idea that humans originated via evolution rather than by supernatural design. Moreover, studies demonstrate that even biology teachers have difficulty teaching their students about evolution, often including creationist explanations as well. A typical response to such findings is the argument that greater exposure to evolutionary theory would eliminate these unscientific alternatives. However, creationist ideas are not easily extinguished. Even after repeated exposure to evolutionary concepts, creationist ideas are more likely to be "incorporated" into hybrid frameworks along with evolutionary ideas, rather than completely rejected. Thus, members of the public often find these ideas complementary rather than contradictory. In this review, we apply dual-process theory to examine individuals' understandings of the origins of species. We describe cognitive biases that operate at the intuitive-autonomous level (system 1), some of which, we argue, anchor belief in supernatural design, and others of which potentially anchor evolutionary ideas. At the other end of the continuum, reflective and abstract reasoning (system 2) processes are apparent in both scientific and theological explanations of origins. We conclude that presenting supernatural and natural explanations of biological origins as contradictory belies the way they function in everyday reasoning. By understanding the theological and the scientific arguments as well as the way most people intuitively reason about such existential questions, teachers might be better prepared to deal with these issues in the classroom. (Contains 1 table.)