The purpose of this study was to investigate whether there are developmental differences in teleological and anthropomorphic reasoning and whether biology students differ from non?biology students in teleological and anthropomorphic reasoning. The 168 high school and university participants responded to a Microcomputer?based Interactive Test (MBIT) which identified their anthropomorphic/teleological versus causal reasoning patterns. The findings of the study indicate that maturation contributes to the development of causal, non?teleological reasoning between tenth and twelfth grade. It was also shown that the study of biology is a major factor influencing the ability to distinguish between teleological and causal non?teleological reasoning. The educational implications of the study refer to the need to deal with the issue of causal, non?teleological reasoning explicitly and repeatedly during the study of biology.