Nine hundred fifty-four students in a large university nonmajors biology course were pretested to determine the extent to which they held nonscientific beliefs in creationism, orthogenesis, the soul, nonreductionism, vitalism, teleology, and nonemergentism. To test the hypothesis that hypothetico-deductive reasoning skills facilitate movement away from nonscientific beliefs, the degree to which those nonscientific beliefs were initially held and the degree to which they were modified during instruction were compared to student reasoning level (intuitive, transitional, reflective). As predicted, the results showed that the less skilled reasoners were more likely to initially hold the nonscientific beliefs and were less likely to change those beliefs during instruction. It was also discovered that less skilled reasoners were less likely to be strongly committed to the scientific beliefs.