Asia-Pacific Forum on Science Learning and Teaching, Volume 6, Issue 1, Article 6 (Jun., 2005)
Ke-Sheng CHAN
Case studies of Physics graduates' personal theories of evolution
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Research design and data analysis

This study aims to explore two physics graduates' personal theories of evolution through the use of semi-structured, individual interviews, which focus on issues related to the mechanisms of evolution. Its research design and methods of data analysis are described below.

The subjects and context of interviews

The subjects of the interviews were two male physics doctoral students at a large, central Texas university. One is a 29-year-old student from India (student A); the other is a 27-year-old student from Taiwan (student B). Both students had strong background in physics and math and both were actively involved in major research projects in high-energy nuclear physics. Furthermore, both of them have previously taken at least two years of biology in either high school or universities.

All interviews were conducted during the lunch hour in the graduate student office where the students work and study, using the techniques of research on conceptual change to elicit students' genuine physicist's conceptions about evolution in the "real world" situations rather than the "correct" textbook explanations they used in the "science contest" situations. Generally speaking, the atmosphere in their (working and studying) place was casual, relaxed and intellectually demanding and thus provided an excellent environment for the students to comfortably and seriously talk about their ideas in science. To make sure they were "telling the truth," both students were told and agreed to explain their personal understanding about some interesting questions in biology without worrying about its "correctness" prior to the interview.

The semi-structured interviews, which consisted of four open-ended, free-response questions, were quite open and flexible so that students could explain their understandings and clarify their meanings fully and uninhibitedly, both before and after further thought. Whenever possible, the interviewer (the author) has tried to make sure that the four questions were asked in the same order to each student, and that students were not interrupted during their answers and further probing questions were not given until students had finished their answers to their own satisfaction. Also, the interviewer deliberately avoided using any scientific terms in the interviews, such as "evolution" and "natural selection" that might direct the students away from constructing their own explanations about evolution towards recalling the standard "correct" answers in textbooks. Each of the interviews lasted about an hour and both were audiotaped and subsequently transcribed in full by the author.

The interview questions

The interviews centered on the following four open-ended, free-response questions designed to probe students' conceptions about the topic of evolution of traits by means of natural selection and random mutations. Three of these questions were adapted from Brumby (1984) and Bishop & Anderson (1990). The remaining classic question on giraffes' long necks was included partly because the author was interested in finding out what his colleagues thought about the same question that baffled him before (and subsequently inspired this study).

Question 1:
How do you think giraffes develop their long necks?

Question 2:
Cheetahs (large African cats) are able to run faster than 60 miles per hour when chasing prey.
Assuming their ancestors can only run 30 miles per hour, what ideas do you have about how today’s cheetahs could develop the ability to run as fast as 60 miles per hour?

Question 3:
Cave salamanders today are blind (they have eyes that are nonfunctional), though their ancestors used to be able to see.
How would you explain how blind cave salamanders today evolved from their sighted ancestors?

Question 4:
Aerosol insecticides were highly effective in killing mosquitoes when first introduced, but today, about 30 years later, they have become much less effective.
How do you think this could happen?

The first question is designed to both engage students in seriously thinking about questions related to evolution and encourage them to talk about the familiar phenomenon of evolution that they have come to know and often accept without further thought. This question also provides the most reliable information about students' initial spontaneous conceptions of evolution, which may be different from the modified and often more refined conceptions at the end of the interview.

Questions 2 and 3 are intended to reveal students' overall understandings of natural selection and the random genetic processes of mutation and sexual recombination in the neo-Darwinian synthesis of evolution from two different perspectives. Question 2 involves the improvement/appearance of a particular trait whereas question 3 involves the deterioration/disappearance of a particular trait as a result of evolution. Because successfully answering both questions requires a thorough understanding of the interplay between random genetic changes (due to mutations and sexual recombination of genes) and natural selection in the process of evolution, this pair of questions can effectively reveal students' misconceptions about natural selection and the mechanisms of evolution. For instance, they can reveal the common misconceptions held by students that the environment alone (rather than random genetic changes and natural selection) causes traits to change over time, that organisms evolve the traits they need (rather than new traits appear by chance), and that the quality of traits (rather than the proportion of individuals with certain traits) changes from one generation to the next.

The purpose of question 4 is essentially the same as that of questions 2 & 3. In addition to revealing students' misconceptions, the insecticide question is relevant to their everyday lives and serves well to check the consistency of their interpretations in different contexts.

Data analysis

Analysis of students' interview responses was done in two cyclical stages. First, the author reconstructed a tentative description of student conceptions about evolution organized around their understandings of evolution previously found problematic for many university students after formally studying evolution (Brumby, 1979, 1984; Bishop & Anderson, 1990) by identifying key concepts and phrases used by students in their interview responses. Next came the verification stage. The reconstructed description of student conceptions along with the transcript of the interview were first read and carefully checked by the student himself. Any inaccuracies and misinterpretations found were then pointed out to the author and further clarified by the student in follow-up interviews. Following the interview, a new cycle of reconstruction (revision) and verification began and it continued until a student-approved true description of student conceptions was finally achieved. The validated descriptions of student conceptions were further analyzed and compared with the corresponding scientific conceptions to determine the nature of their understandings/misunderstandings about natural selection and the mechanism of evolution.

 

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