Case studies of Physics graduates' personal theories of evolution

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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Analysis of students' ideas

From the way they talked about evolution in the interviews, one could clearly sense that both students A & B believed that they already had a basic understanding of the theory of evolution. However, the analysis of their interview responses below showed that their understandings about (1) the mechanisms of evolution of traits over time and (2) the nature of change in evolution of traits over time were very different from those accepted by most biologists. Furthermore, their conceptions about the mechanisms of evolution and the nature of evolutionary change were found very similar to the common sense "intuitive Lamarckism" misconceptions prevalent among many university students (Bishop & Anderson, 1990; Brumby, 1984) and most secondary boys before they were taught evolution (Deadman & Kelly, 1978). The following describes some important aspects of students' conceptions about evolution by contrasting their ideas with those currently accepted by biologists.

The mechanisms of evolution of traits over time

How does evolution of traits over time come about? To answer this question, biologists recognize that there are two distinct processes influencing traits exhibited by populations over time and they are fundamentally different in cause and effect. Namely, new traits (a) originate due to random changes in genetic materials (caused by random mutation or sexual recombination) and then (b) survive or disappear as a result of selection by environmental factors (i.e., natural selection). Thus, most biologists today believe that the evolution of traits over time is caused by the combined effects of random genetic changes and natural selection.

In contrast to the scientific views, both students A & B believed that the evolution of traits over time occurs solely as a result of environmental pressures and that there is only one single process (called adaptation) in which characteristics of the species gradually change over time.

The idea of environmental pressures as the sole cause of evolutionary change in traits over time plays the central role in students' conceptions about the mechanisms of evolution of traits over time. Both students A & B invariably used environmental pressures as their sole explanation about how and why evolution of traits comes about in their responses to all interview questions. They believed that environmental pressures, rather than random genetic changes and natural selection, cause traits to change over time and claimed that environmental pressures exert their influences by creating a need/no need for organisms to develop/discard certain traits over time in order to survive.

Examples:

Student A: if an organism finds that it has to do something...then...uh...then...uh... because of certain environmental pressure and stuff like that, it develops characteristics which is slowly over a period of time......

Student A: Well, because they need longer necks to reach their food, they...uh...somehow managed to use their necks to reach the trees......

Student B: ......cave salamanders always live in the caves, they don't need their eyes anymore. Uh...this is also evolution, only in an opposite direction. Because they don't need the eyes then the eyes disappear.

Failing to make a distinction between the appearance of traits in a population and their survival over time and recognize the fact that the environment does not cause new traits to appear but only "select" them after their appearance, both students insisted that environmental pressures alone will require and "somehow" empower organisms to develop the needed traits over time in order to survive. When asked to explain exactly "how" the organisms acquire the needed traits for survival under environmental pressures, students often gave typical single-process Lamarckian explanations (repeated use/disuse resulted in change in traits), indicating that they believed there is only a single process in which traits of organisms gradually change over time.

Examples:

Student B: ......In cheetahs’ case, there is a pressure forcing them to run fast in order to survive. They did their best to run fast in order to catch the prey, and slowly they developed the ability to run faster and faster over each generation.

Student A: .....over a period of time, an organism finds that it really doesn't need an organ of its body and...uh...physically that organ might be there but the organism might just not use it. Like in this case, we have the eyes but the eyes are useless and become blind.

In their alternative single-process accounts of the mechanism of evolution, students seemed to incorporate the two distinct processes of random genetic changes and natural selection into one single process called (by them) adaptation. By using the everyday meaning of this word, namely individuals respond to environmental conditions by altering their form, function or behavior through their own efforts, they frequently interpreted evolution as a purposeful and active process of adapting to the environment by organisms in order to survive.

Examples:

Student A: ......I mean, it’s...went back to our business of giraffes...uh...uh...it’s like they had to adapt to the situation where less grass was on the ground and more trees and...uh...they slowly developed the characteristics in order to survive.

Student B: Uh...all creatures want to survive, in order to survive they need to adjust themselves to adapt to their living environments. If the outside environments change, they must change accordingly, otherwise they will become extinct......

Interestingly, students' alternative interpretation of the meaning of adaptation in evolution above fits so nicely with their previous alternative conception that environmental pressures cause both the initial appearance and the subsequent development of new traits that they tend to reinforce each other. Partly due to the apparent simplicity and self-consistency of these ideas, students consistently used both of them to explain how evolution of traits comes about in answering the interview questions and in the process have successfully constructed an environmentally driven single-process misinterpretation of the mechanism of evolution of traits over time. This naive misconception about how evolution of traits over time comes about, which was found commonly held and extensively used by both students, can be summarized as follows:

Evolution of traits over time occurs as a result of environmentally induced and directed adaptation by organisms.

The nature of change in evolution of traits over time

What changes in the evolution of traits over time? According to biologists, new traits arise through random, discrete genetic changes involving individual organisms. Those traits then gradually become established in a population as the proportion of individuals in a population possessing those traits grows with each succeeding generation. Therefore, it is the proportion of individuals in a population with discrete (adaptive) traits that gradually changes in evolution of traits over time.

Instead of attributing the evolutionary change of traits over time to the changing proportion of individuals possessing the adaptive traits, both students A & B asserted that the quality of the adaptive traits gradually improves/deteriorates over each generation in the process of evolution.

Examples:

Student A: Well, because they need longer necks to reach their food, they...uh...somehow managed to use their necks to reach the trees. Gradually their necks became longer and longer over each generation.

Student B: ......In cheetahs’ case, there is a pressure forcing them to run fast in order to survive. They do their best to run fast in order to catch the prey, and slowly they can run faster and faster over each generation.

By assuming that the improved traits acquired by the process of “adaptation” can be passed on to the next generation (i.e. acquired traits can be inherited) and that evolution changes the traits of individuals in populations as a whole (i.e. variation within populations is of little significance in evolution), both students interpreted the evolution of traits over time as a gradual “quality-change” process in which “insects become more immune, rather than more insects become immune.” (Brumby, 1984, p. 499) Their alternative conceptions concerning the nature of change in evolution of traits over time can be summarized as follows:

The quality of traits changes gradually over generations in evolution.
Acquired traits can be inherited.
Variation within populations is of little significance in evolution.

Examples:

Student A: Well, because they need longer necks to reach their food, they.…..managed to use their necks to reach the trees. Gradually their necks became longer and longer over each generation.

Student B: ...... They tried hard to stretch their bodies towards higher trees, as a result, their necks became longer and longer over each generation.

Summary

The above analysis clearly shows that the two physics doctoral students interviewed did not have a basic understanding about the theory of evolution. Their common sense knowledge about evolution is in fact very similar to the popular “intuitive Lamarckism” shared by many contemporary high school and college students. Instead of gaining a sound understanding of the two-process neo-Darwinian synthesis of evolution (i.e. the theory of evolution by natural selection and random genetic changes) from their previous biology education, they have constructed a deceptively simple and coherent single-process "physicist" synthesis of evolution (i.e. the theory of evolution by environmentally driven adaptation) consisting of the following four internally consistent and mutually supportive misconceptions.

(1) Evolution of traits over time occurs as a result of environmentally induced and directed adaptation by organisms.
(2) The quality of traits changes gradually over generations in evolution.
(3) Acquired traits can be inherited.
(4) Variation within populations is of little significance in evolution.

Copyright (C) 2005 HKIEd APFSLT. Volume 6, Issue 1, Article 6 (Jun., 2005). All Rights Reserved.

Student A:	if an organism finds that it has to do something...then...uh...then...uh... because of certain environmental pressure and stuff like that, it develops characteristics which is slowly over a period of time......
Student A:	Well, because they need longer necks to reach their food, they...uh...somehow managed to use their necks to reach the trees......
Student B:	......cave salamanders always live in the caves, they don't need their eyes anymore. Uh...this is also evolution, only in an opposite direction. Because they don't need the eyes then the eyes disappear.

Student B:	......In cheetahs’ case, there is a pressure forcing them to run fast in order to survive. They did their best to run fast in order to catch the prey, and slowly they developed the ability to run faster and faster over each generation.
Student A:	.....over a period of time, an organism finds that it really doesn't need an organ of its body and...uh...physically that organ might be there but the organism might just not use it. Like in this case, we have the eyes but the eyes are useless and become blind.

Student A:	......I mean, it’s...went back to our business of giraffes...uh...uh...it’s like they had to adapt to the situation where less grass was on the ground and more trees and...uh...they slowly developed the characteristics in order to survive.
Student B:	Uh...all creatures want to survive, in order to survive they need to adjust themselves to adapt to their living environments. If the outside environments change, they must change accordingly, otherwise they will become extinct......

Student A:	Well, because they need longer necks to reach their food, they...uh...somehow managed to use their necks to reach the trees. Gradually their necks became longer and longer over each generation.
Student B:	......In cheetahs’ case, there is a pressure forcing them to run fast in order to survive. They do their best to run fast in order to catch the prey, and slowly they can run faster and faster over each generation.