5 THE LIVING ENVIRONMENT
5F) EVOLUTION OF LIFE
Natural selection. High-school and college students, even after some years of biology instruction, have difficulties understanding the notion of natural selection (Brumby, 1979; Bishop & Anderson, 1990). A major hindrance to understanding natural selection appears to be students' inability to integrate two distinct processes in evolution, the occurrence of new traits in a population and their effect on long-term survival (Bishop & Anderson, 1990). Many students believe that environmental conditions are responsible for changes in traits, or that organisms develop new traits because they need them to survive, or that they over-use or under-use certain bodily organs or abilities (Bishop & Anderson, 1990). By contrast, students have little understanding that chance alone produces new heritable characteristics by forming new combinations of existing genes or by mutations of genes (Brumby, 1979; Clough & Wood-Robinson, 1985b; Hallden, 1988). Some students believe that a mutation modifies an individual's own form during its life rather than only its germ cells and offspring (see almost any science-fiction movie). Students also have difficulties understanding that changing a population results from the survival of a few individuals that preferentially reproduce, not from the gradual change of all individuals in the population. Explanations about "insects or germs becoming more resistant" rather than "more insects or germs becoming resistant" may reinforce these misunderstandings (Brumby, 1979). Specially designed instruction can improve students' understanding of natural selection (Bishop & Anderson, 1990).
Adaptation. Middle-school and high-school students may have difficulties with the various uses of the word "adaptation" (Clough & Wood-Robinson, 1985a; Lucas, 1971; Brumby, 1979). In everyday usage, individuals adapt deliberately. But in the theory of natural selection, populations change or "adapt" over generations, inadvertently. Students of all ages often believe that adaptations result from some overall purpose or design, or they describe adaptation as a conscious process to fulfill some need or want. Elementary- and middle-school students also tend to confuse non-inherited adaptations acquired during an individual's lifetime with adaptive features that are inherited in a population (Kargbo et al., 1980).
Evolution and reasoning ability. Some research suggests that students' understanding of evolution is related to their understanding of the nature of science and their general reasoning abilities (Lawson & Thomson, 1988; Lawson & Worsnop, 1992; Scharmann & Harris, 1992). Findings indicate that poor reasoners tend to retain nonscientific beliefs such as "evolutionary change occurs as a result of need" because they fail to examine alternative hypotheses and their predicted consequences, and they fail to comprehend conflicting evidence. Thus, they are left with no alternative but to believe their initial intuitions or the misstatements they hear.