This paper reports data from a study aiming to explore secondary students' preconceptions and explanations about evolutionary processes. Students may exhibit both alternative and scientifically acceptable conceptions and bring different ones into play in response to different problem contexts. Hence, the examination of their explanations before instruction within different problem contexts is expected to highlight the concepts that instruction should put more emphasis on. To achieve this, an open-ended questionnaire in conjunction with semi-structured interviews was used to allow students to express their own views on issues related to evolution. Students' explanations highlighted their lack of knowledge of important evolutionary concepts such as common descent and natural selection. In addition, many students explained the origin of traits as the result of evolution through need via purposeful change or as carefully designed adaptations. Rather than evolutionary, final causes formed the basis for the majority of students' explanations. In many cases students provided different explanations for the same process to tasks with different content. It seems that the structure and the content of the task may have an effect on the explanations that students provide. Implications for evolution education are discussed and a minimal explanatory framework for evolution is suggested.

This study aimed to explore secondary students' explanations of evolutionary processes, and to determine how consistent these were, after a specific evolution instruction. In a previous study it was found that before instruction students provided different explanations for similar processes to tasks with different content. Hence, it seemed that the structure and the content of the task may have had an effect on students' explanations. The tasks given to students demanded evolutionary explanations, in particular explanations for the origin of homologies and adaptations. Based on the conclusions from the previous study, we developed a teaching sequence in order to overcome students' preconceptions, as well as to achieve conceptual change and explanatory coherence. Students were taught about fundamental biological concepts and the several levels of biological organization, as well as about the mechanisms of heredity and of the origin of genetic variation. Then, all these concepts were used to teach about evolution, by relating micro-concepts (e.g. genotypes) to macro-concepts (e.g. phenotypes). Moreover, during instruction students were brought to a conceptual conflict situation, where their intuitive explanations were challenged as emphasis was put on two concepts entirely opposed to their preconceptions: chance and unpredictability. From the explanations that students provided in the post-test it is concluded that conceptual change and explanatory coherence in evolution can be achieved to a certain degree by lower secondary school students through the suggested teaching sequence and the explanatory framework, which may form a basis for teaching further about evolution.

In this paper, the main points of Lamarck's and Darwin's theoretical conceptual schemes about evolution are compared to those derived from 15 years old students' explanations of evolutionary episodes. We suggest that secondary students' preconceptions should not be characterized as ''Lamarckian'', because they are essentially different from the ideas that Lamarck himself possessed. Most students in our research believed that needs directly impose changes on animal bodies in order to survive in a given environment and accepted the possibility of extinction whereas Lamarck believed that it was the effect of use or disuse that would produce changes on body structures and that species would transform but would not die out. We conclude that the relationship between secondary students' ideas and historical views on evolution should be treated more skeptically, given the differences in the historical, social and cultural contexts, and that instruction should focus on students' ideas of needdriven evolution as well as on the role of chance in the evolutionary process.