Sometimes I wish I taught quantum physics. My students would be convinced it is hard science, many would have very little background knowledge of the subject and no moral objections would be raised. Instead, I teach ULS2202 "Evolution" under the University Scholars Programme (USP) and LSM3252 "Evolution and Comparative Genomics" under the Life Sciences Programme, where a large proportion of my students come to class armed with religiously motivated objections to the subject. Thus, unlike other modules, evolution lecturers do not have the luxury of starting on a 'clean slate' when they teach this subject. Past surveys revealed that while most NUS students were never taught evolution in school, many believed they understood the subject from discussions with parents and friends and TV shows they had seen.

What is the best approach for dealing with this challenge? With evolution playing a central role in the life sciences, this issue is actively discussed by biologists and organisations such as the National Academy of Sciences and Institute of Medicine (2008). Among the more controversial issues being raised is whether objections to evolution in the form of 'intelligent design' (a secular version of creationism) should be covered in a science class. Scott and Branch (2003) argue that such alternatives to established theories should not be mentioned unless they meet the following criteria:

• Students are interested in the controversy.
• The scientific community accepts that these issues are valid for discussion.
• The issues are well documented.
• All aspects of the arguments have been well thought out and are intellectually stimulating.
• The issues are easily understood by students.

According to Scott and Branch (2003), the 'evolution versus intelligent design' debate fails to meet some of these requirements and thus should not be covered. However, I would argue that Scott and Branch overlook the fact that students come to evolution classes armed with these objections, which makes addressing them unavoidable. I was initially unaware of the widespread skepticism among NUS students towards evolution and only realised late in my first semester in Singapore, during Academic Year 2002/2003, that Scott and Branch's approach does not work as students end up being detached from the subject. For them, the burning question is finding out why evolution should be preferred over 'intelligent design' and not whether a particular model, for example, offers the best explanation for sexual selection. As such, ignoring the controversy is not an option.

To deal with these challenges , I adopt a constructivist's approach to teach evolution (Scott & Branch, 2003). This approach uses the debate to illustrate how Science uses evidence to select from among competing hypotheses. To implement this approach effectively, students have to be actively involved in characterising the alternatives to accepted scientific theories and be directly exposed to relevant evidence. For example, in ULS2202 I introduce evolution, while I ask students to use resources of their own choosing to define the main elements of 'intelligent design'. They soon realise that 'intelligent design' is mostly a collection of objections against evolution, and offers no alternatives to theories such as the Tree-of-Life and only nebulous notions about the origins of adaptations.

A similar approach can be adopted to address other objections against evolution. Students are asked to collect these objections, which are generally about the existence of supposedly 'irreducibly complex systems' and the 'lack of transitional fossils'. The first objection can be challenged using examples such as the gradual evolution of the vertebrate eye (Nilsson & Pelger, 1994). Similarly, exposing students to 't ransitional' fossils effectively counters the second objection. For example, one practical session in ULS2202 and LSM3252 is devoted to gathering morphological differences between human and chimpanzee skulls. After t hese differences have be en characterised , skulls from human fossil records are introduced for compa rison. Students realise that these skulls display a mosaic of ape- and human-like features and that the older fossils are more apelike. Exposing students to molecular evidence is another powerful method of addressing such objections. In another practical session, they learn to reconstruct evolutionary trees based on mitochond r ial gene s for mon keys, apes, Neanderthals and humans. They discover that the common ancestry of humans and chimps and the intermediacy of Neanderthals is still supported even when 95% of all evidence is deleted or only synonymous mutations are considered (Wildman et al., 2003).

Based on my experience, I believe that using the constructivist's approach to 'teach the controversy' is more productive than ignoring it. As we address these controversies, students also learn to gather and evaluate evidence from a scientific perspective.

Publicity E-poster for ULS2202 Evolution. Reprinted with permission from the University Scholars Programme

References

National Academy of Sciences and Institute of Medicine (2008). Science, Evolution and Creationism. Washington DC: National Academies Press.

Nilsson, D. E. & Pelger, S. (1994). 'A Pessimistic Estimate of the Time Required for an Eye to Evolve'. Proceedings of the Royal Society of London, Series B, Vol. 256, pp. 53-58.

Scott, E.C. & Branch, G. (2003). 'Evolution: What's Wrong With '"Teaching the Controversy".' Trends in Ecology & Evolution, Vol. 18, Issue 10, pp. 499-502.

Wildman, D. E., Uddin, M., Liu, G., Grossman, L. I. & Goodman, M. (2003). 'Implications of Natural Selection in Shaping 99.4% Nonsynonymous DNA Identity Between Humans and Chimpanzees: Enlarging Genus Homo.' Proceedings of the National Academy of Sciences USA, Vol. 100, Issue 12, pp. 7181-7188.