The present study investigates how Greek in-service secondary education biology teachers understand the unique features of school biology and physics when considering the biological theoretical edifice and method. Our theoretical framework focuses on important differences that exist between the neo-Darwinian and Newtonian worldviews, while our methodology involves questionnaires and mainly individual interviews with fourteen (14) biology teachers. The study findings indicate that biology teachers encounter difficulties in unraveling the distinction between nomothetic and non-nomothetic natural sciences and in understanding the historical character of biology. They also emphasize the importance of scientific laws and experimentation when considering the epistemological features of biology, and the reason is that they reflect on the issue of what science or scientific knowledge is by simultaneously adopting two contradictory perspectives. On the one hand, they stress what a science should be if it is to be called 'science', and on the other hand, they focus on how a particular science, such as biology behaves. Unavoidably, a logical tension is created in their minds, and as a way of solving this tension, they view biology as being in a state of ongoing change towards an ideal, and, in many aspects, a positivistic pattern of science.