The concept of biological evolution within populations, or genetic change over time to populations, is a central principle of biological science; "Nothing in biology makes sense except in the light of evolution" (Dobzhansky, 1973). However, national polls show that over 45% of Americans do not accept the theory of evolution by natural selection (Quammen, 2004). Moreover, in the debate about whether or not evolution should be taught in schools, we have lost sight of what students really understand about the process of natural selection and its role in evolution.
Educating students about the process of evolution through natural selection is vitally important because not only is it the unifying theory of biological science, it is also widely regarded as difficult for students to fully comprehend (Sandoval, 2003). Anderson and colleagues (2002) describe alternative ideas and misconceptions about natural selection as highly resistant to change. Catley (2006) suggests that the educational emphasis on microevolutionary processes has left both teachers and students with a poor understanding of macroevolution and speciation.
To truly understand evolution, students need to understand other basic biological processes. Educational literature confirms that comprehension of evolution is made possible through the understanding of the individual concepts that comprise the theory (Passmore & Stewart, 2000). Even when students do grasp the basic idea of natural selection, the underlying concepts may be unclear (Kadury-Slezak, 2001). Many students also tend to view individual organisms as representative of entire populations and fail to recognize population variation as necessary for evolutionary change; thus students do not distinguish between individuals and species when describing selection (Greene, 1990; Hallden, 1988). Such typological thinking can lead to a belief that organisms have the power to change their traits in response to the environment, particularly when students fail to understand mechanisms of inheritance (Helm, 2002; Sandoval, 2003; Wood-Robinson, 1995).
Compounding the problem is that in many courses of study, students' experience with science is merely a survey of information without any meaningful exposure to the process that produced the information (Clough & Olson, 2004). This missing component of science education is evident in the public's lack of understanding about what constitutes a scientific theory (McComas, 2004). In science, a theory is an explanation based upon extensive testing that is well-supported by the accumulation of evidence. When students are not exposed to studies in the nature of science, they are not able to distinguish between a scientific theory and the vernacular usage of theory to mean a guess or an unsupported explanation (Backhus, 2004). This discrepancy between a scientific theory and a personal theory is of particular relevance to evolution education because one of the common misconceptions about evolution is that it is "just a theory."
Instruction that highlights the nature of scientific thought is the key to students' understanding about natural selection. Instruction in evolution must therefore focus also on the epistemic thinking that has led to the development of evolution theory as the best scientific explanation we have for the diversity of life on Earth. According to Sandoval (2003) such instruction should include scientific epistemological components like causal explanations, parsimony in developing conclusions, accounting for observations in explanations, and reliance on creativity. If students have a basic knowledge of the nature of science, their development of explanatory models can actually reconstruct the concept of natural selection (Passmore & Stewart, 2000). Conceptualization of the scientific process also helps students understand why scientists consider natural selection to be a strongly-supported theory and the best explanation for life's diversity (Backhus, 2004). …