In this study we aim to find out whether a training program for secondary school science teachers which was organized based on the model of Pedagogical Content Knowledge (PCK), could improve their individual PCK for a specific scientific issue. The Evolution Theory (ET) and the Natural Selection (NS) were chosen as the scientific issues of interest. Both of them are fundamental in biology teaching, especially the ET which can be taught as a unifying theory of biology. The individual PCK of teachers can be improved by strengthening its components: knowledge, pedagogy and managing the context. The principals and content of the seminar were decided based on the results of another study among Greek teachers for the characteristics of their PCK about ET, NS and Nature of Science (NoS). The seminar involved 16 secondary school teachers. We found that all trainees improved their individual PCK and felt adequate to teach more effectively the ET and the NS to their students. All participants through the activities they performed, moved to a more constructive and learner-centered teaching style compare to what they used to do before the training program.