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A scoring rubric for students' responses to simple evolution questions: Darwinian components.

The call to wit, It students Darwin's theory of evolution by natural selection has been made by a variety of professional organizations (e.g., American association for the Advancement of Science, 198,9; National Academy of Science, 1998; National Association of Biology Teachers, 1995; National Science Teachers Association, 1997). In addition to these national organizations, almost every state has science education guidelines calling for the teaching of evolution (Lerner, 2000; Moore, 2002).

Many administrators and policymakers believe that evolution is being taught, but teachers know that it is far more important that evolution be learned. Standards and curriculum documents frequently specify what is to be taught, but then provide little help with assessment and evaluation. This paper provides .t scoring rubric that will help teachers evaluate students' understandings of biological evolution.

Background

In 1859 Charles Darwin published On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life. Modifications to his initial theory were made in the mid-1900s in what is now called "the new synthesis" or "die modern synthesis," by scientists such as Theodosius Dobzhansky, Gaylord Simpson, and others. I here modifications included the fields of embryology, systematics, and genetics that were advancing rapidly since Darwin's time. Despite these and other modifications, the core of Darwin's theory remains unchanged to this day. The following outline of Darwin's theory will contain terms and concepts that were not known to Darwin, but cart easily be assimilated into his original theory; Darwin's original ideas remain the backbone of modern evolutionary theory.

Darwin's theory is complex in that many students, teachers, and even scientists frequently misunderstand and misuse it (Anderson, Fisher S: Norman, 2002; Bishop & Anderson, 1990; Rudolph & Stewart, 1998). However, its framework cart be divided into four straightforward components.

Darwinian Component #1: Variation

There exists within every population variation among individuals; the origin of that variation is chance.

Darwin did not know of DNA, gene expression, or mutations, but he did observe variation within species. Darwin viewed the origin of variation as being chance. (The idea of chance as a driving force in nature is at the core of Darwin's theory, and is also central to the conflict,' debate with creationists.) Why does one bird feed at a different time than another? Why is one fish a different color than another? Why is one cheetah faster than another? Darwin in saw it all as being related to chance. The term "random" and the concept of mutations are two related items that fit into this component of Darwin's theory. Students' responses are frequently full of buzzwords, such as mutation, that are associated with evolution. Simply slating "there was a initiation' does not represent much comprehension, but if associated ideas are also included, there then exists evidence that a student has a beginning understanding of evolutionary processes.

Darwinian Component #2: Genetics

Organisms pass information front one generation to the next.

A large section of this second component now relates to Medelian genetics, which post-dated Darwin, but he knew that something (i.e., information) was passed from generation to generation. Darwin developed his own theory of genetics that was based on blending inheritance-units called "gemmules," but that effort proved fruitless (Mayr, 1982). For students to rise this component, they must use phrases such as "the genes were passed to the next generation," or "information was passed to the next generation." Some students have difficulties with genetics concepts, which can be a significant barrier to a thorough understanding of evolution (e.g., Lawson & Thompsort, 1988).

Darwinian Component #3: Differential Survival & Reproduction

There occur in nature events in which some organisms die and others survive. However, over long periods of time, population size remains relatively stable.

This, the broadest of the four Darwinian components, covers the concepts of fitness, struggle for existence, limitations in resources, and differential rates of death and reproduction. Some ideas here pre-date Darwin. For example, Thomas Malthus, in his 1826 essay on the principles of population dynamics (Malthus, 1826), proposed that limitations in resources would lead to a struggle for existence. Students frequently use the phrase "survival of the fittest" when they are trying to communicate the idea of "struggle for existence," which may relate to a misunderstanding of the term "fitness." Fitness relates directly to reproductive success (as opposed to strength and/ or speed). For example, if the fastest and most powerful lion is sterile, its fitness is zero; it will have no genes represented in the next generation, and thus becomes an evolutionary dead-end.

Darwinian Component #4: Change Over Time

Over time, the percentage of a population that possesses an adaptive trait increases in frequency. This is the concept of adaptation.

Any behavior, anatomical structure, or physiological process that provides some advantage over other individuals is an adaptation. Multiple generations, and sometimes many thousands of years, are required for an adaptation to become common within a population. Students frequently include phrases such as "they adapted" in their answers; to many students, this answer means that some individuals within the population mutated and became "better." It is important to note that adaptation is a population event, and does not relate to individuals. Additionally, mutations are the source of all novel traits, some of which become adaptations, hill many others that become reproductive dead-ends. "Perfectly adapted" is a common phrase of students that makes no sense in biology (e.g., "Dolphins are perfectly adapted to their aquatic environment"). A species is either adapted or it is not adapted--it either survives or it goes extinct.

Using the Rubric

We used the previous four Darwinian components to create a scoring rubric (Figure 1) to score students' answers to simple evolution questions. The rubric has been used by different instrtuctors, who established an inter-rater reliability of 85% (Jensen & Finley, 1996).

Students' answers to the following evolution question were used in the developtment of the scoring rubric:
 Cheetahs (large African cats) are able to run
 faster than 60 miles per hour when chasing
 prey. How would a biologist explain how
 the ability to run fast evolved III cheetahs,
 assuming their ancestors could only run 20
 miles per hour?

Bishop car Anderson, 1990


Students' answers to the above question vary widely in quality and number of Darwinian ideas, and like most students' answers, contain ideas that don't fit into any of the four categories. The following example responses, taken from freshmen biology students, show a progression in understanding in that they contain more and more Darwinian ideas. In each answer, Darwinian components are classified into one of the four categories. It is important to note that not every word or idea in a students response can be classified within this rubric, some phrases, and even a few entire sentences, contain nothing germane to Darwin's theory and many do not even contain non-Darwinian ideas. In those cases, no coding is used. Additionally, some answers will have more than one answer/idea within a single category. For example, a student may use the idea of initiation as a source of variation, and then also state that chance was involved. Our experience with this rubric suggests a binary system of scoring; either there is, or is not, evidence that a student's response contains ideas or concepts from a specific Darwinian category (as opposed to awarding multiple points within each category).

Example #1

Student's answer: The cheetahs adapted to their environment.

Scoring:

Darwinian Component #1: 0

Darwinian Component #2: 0

Darwinian Component #3: 0

Darwinian Component #4: 0

Scoring note: A score of 1 indicates that a word or phase was identified for this category, whereas a 0 indicates that no phrases or words were identified that met the requirements of the category.

Adaptation is too complex a process to award any points for this simple answer. It is responses like this one that cause teachers to write, for example, "Responses must contain more than 15 words." There arc nines when simple answers are appropriate, but this answer fails to provide evidence about this student's understanding of biological evolution.

Example #2

Student's answer: The cheetahs mutated and became faster. They mutated until they could run 60 mph.

Scoring:

Darwinian Component #1: 1 (mutated)

Darwinian Component #2: 0

Darwinian Component #3: 0

Darwinian Component #4: 0

This response contains one idea that is consistent with Darwinian evolution, that being the notion of a mutation. But this scoring is generous in that other issues are not included in the student's answer. Many students know that the word "mutate" is key to evolution, indeed "mutation" is identified for Darwinian Component #1 in the rubric. The above answer shows that the student knows that mutations Could lead to increased speed. However, by stating that "the cheetahs mutated," it seems that the student thinks that all the cheetahs mutated at the same time, and thus does not understand variation within the population of cheetahs. This is inconsistent with Darwinian Component #1, and is a misconception about the frequency of mutations within populations.

[ILLUSTRATION OMITTED]

Example #3

Students answer: Some of the cheetahs mutated and the faster ones were better able to catch prey. They evolved until now they can run 60 mph.

Scoring:

Darwinian Component #1: 1 (Some of the cheetahs mutated.)

Darwinian Component #2: 0

Darwinian Component #3: 1 (The faster ones were better able to catch prey.)

Darwinian Component #4: 0

This student implies variation within the population by stating that "Some of the cheetahs mutated" and also states that the faster cheetahs had an advantage over the slower cheetahs (i.e., "Faster ones were better able to catch prey"). The phrase 'They evolved until now they can run 60 mph" does riot contain any mechanism for evolution and is not coded. (Note: Sonic instructors would not agree that this answer meets the criteria for Darwinian Component # 1 because technically cheetahs can't mutate, but rather a cheetah's genes mutate. The level of precision required within students' answers is highly variable between instructors.)

Example #4

Student's answer: Some of the cheetahs were able to run faster than other cheetahs. The faster one had kids were faster than the others.

Scoring:

Darwinian Component #1: 1 (Some ... were ... faster ... than others.)

Darwinian Component #2: 1 (Tire faster ones had kids that were faster.)

Darwinian Component # 3: 0

Darwinian Component #4: 0

Without going into the depths of genetics, this response indicates that something (speed, in this case) is being passed from one generation to the next. The text in this response is probably the minimal content required to fulfill the Darwinian Component #2 category.

Example #5

Student's answer: Some were fast and others were slow. The fast ones had an advantage in that they were able to catch more food. The slower ones straved. The fast one evolved to 60 mph.

Scoring:

Darwinian component #1: 1 (Some were fast and others were slow.)

Darwinian Component #2: 0 Darwinian Component #3: 1 (The fast ones had all advantage.... The slower ones starved.)

Darwinian Component #4: 0

This student recognized that there was variation within the population, and also the advantages and disadvantages that this variation created, which is a component of the Darwin Component #3 category.

Example #6

Student's answer. The faster ones were able to catch more food, and the slower ones had a more difficult time catching food. The faster ones reproduced and had kids that were also fast, and they had an advantage over the kids from the slower ones.

Scoring:

Darwinian Component # 1: 1 (The faster one ... the slower ones.)

Darwinian Component #2: 1 (The faster one.,, reproduced and had kids that were also fast.)

Darwinian Component #3: 1 (The faster ones were able to catch more food, and the slower ones had a more difficult time catching food.)

Darwinian Component #4: 0

This student recognized that there is variation within the population, that the trait of being fast was passed to the next generation, and that there was air advantage to being fast. The word "advantage" is a minimal response for Darwinian Component #3 in that the student does not indicate what that advantage ultimately means (i.e., differential survival and reproduction).

Example #7

Student's answer. There was a mutation in the 20-mile-per-hour cheetahs that allowed some to run faster than the others. The mutated cheetahs were able to catch more food. Their kids inherited the mutation and had a advantage over the kids inherited the mutation. The ones without the mutation became extinct, but the one with the mutation lived on until now they can run 60 miles per hour:

Scoring:

Darwinian Component #1: 1 (mutation, some run faster than others)

Darwinian Component #2: 1 (Their kids inherited the mutation.)

Darwinian Component #3: 1 (had an advantage, the ones without the mutation became extinct.)

Darwinian Component #4: 1 (The ones with the mutation lived on until they could run faster than 60 miles per hour.)

This response did not use the term "adaptation" and misused the term "extinction," but it implies that over time the percentage of faster cheetahs increased. Many teachers would not agree that this student shows an understanding of the concept of adaptation (Darwinian Component #4), but the text can be interpreted to show at least a minimal comprehension. Additionally, the phrase "There was a mutation in the 20-mile-per-hour cheetahs" could be interpreted to mean that adult cheetahs mutated, which would be problematic in terms of how that mutated trait would he passed to the next generation.

Example #8

Student's answer: A long time ago cheetahs could only run 20 miles per hour, but a few of them could run a little faster because of a mutation or something. Those that could run faster had an advantage over the others because they could get more food and stuff. The faster ones gave their kids the mutation and they could run faster than the others. The slow one died and the fast ones lived and had kids. Some of those kids mutated again and became even faster. This happens over and over again until now most all cheetahs can run 60 miles per hour

Scoring:

Darwinian Component #1: 1 (... but a few of there could tun a little faster because of a mutation)

Darwinian Component #2: 1 (The faster ones gave their kids the mutation.)

Darwinian Component #3: 1 (Those that could run faster had an advantage.)

Darwinian Component #4: 1 (This happens over and over again until now most all cheetahs can run 6o miles per hour.)

This student's response better explains adaptation than Example #6, and also does a good job of covering the other Darwinian categories. However, it would be very interesting to have this student explain how the parent cheetahs "gave" the mutation to their kids, and also how the "mutation or something" initially occurred. Could e), elaborate a bit more on the "or something' part of that response? Despite these weakness, this response demonstrates a good understanding of Darwinian evolution.

Conclusion

Consistency is a key factor to grading as well as in using any scoring rubric. It a teacher decides that the mere presence of the word "mutation" is enough to satisfy Darwinian Component #1, he or she must he consistent with that scoring. However, other teachers will not agree with that method and will require the student to explain the source of that mutation. Individual interpretations depend on many factors, including grade level, length of the evolution unit, and even the standards specified by the teacher, department, school, district, and state. Typically, students' use of a single key word, such as "mutation" or "adaptation" for a complex evolution question represents a very minimal understanding, or even rote memorization and does not provide evidence for any depth of understanding, but rather is more of a "stimulus -response" system, e.g., "(I)f there is a question about evolution, just write 'mutation' and you should get at least some credit."

Even when a student's response covers all four Darwinian categories, he or she may not necessarily have an expert level or understanding of evolution. As illustrated in the previous examples, extra or irrelevant words and phrases (e.g., the slower ones went extinct) will make teachers pause to try to interpret the student's intentions. Other phrases (e.g., the faster ones gave their kids the mutation) will provide a glimpse into either a simplified view of biology or potential complex misconceptions.

Research in science education, conceptual change research, cognitive science research, etc., all indicate that students pull together a wide array of information when trying to solve problems (see, for example, Jimenez-Aleixandre, 1996). Some of the information used by students is consistent with current scientific thinking, but much of it is inconsistent, e.g., misconceptions, alternative conceptions, etc. In relation to evolution, many student thoughts are not so much wrong as they are out-of step with more recent scientific advances. For example, some student ideas can be traced back to ideas first documented by Larmarck, e.g., use and disuse of organs, or even William Paley and his ideas or beliefs on natural theology. This article has provided a rubric for classifying the Darwinian components of students' response, but there is still a need in the literature for a rubric outlining the use of "non-Darwinian" ideas that Student,, use in answering evolution questions.

Most teachers know the phrase "teaching to the rest," but now a different cliche can be introduced: "teaching to the rubric." Teaching students the four components of Darwin's theory is an easy and logical introduction to a unit on evolution, but it is important that students can use the rubric to solve novel evolution problems, and not simply recite the key phrases for the four components of Darwin's theory.

References

American Association for the Advancement of Science. (1989). Project 2061. Science for All Americans. Washington, DC: American Association for the Advancement of Science.

Anderson, D. L., Fisher, K. M. & Norman, G. J. (2002). Development and evaluation of the conceptual inventory of natural selection. Journal of Research in Science Teaching, 39(10), 952-978.

Bishop, B.A. & Anderson, C.W. (1990). Student conceptions of natural selection and its role in evolution. Journal of Research in Science Teaching, 27(5), 415-427.

Darwin, C. (1859). On the Origin of Species by Means of Natural Selection, or the Preservation of Favored Races in the Struggle for life. London: Murray.

Jensen, M. & Finley, F. (1996). Changes In students' understanding of evolution resulting from different curricular and instructional strategies. Journal of Science Teaching, 33(8), 879-900.

Jensen, M., Moore, R., Hatch, J. & Hsu, L. A scoring rubric for students' responses to simple evolution questions: Non-Darwinian components. Submitted to The Science Teacher.

Jimenez-Aleixandre, M. P. (1996). Darwinian and Lamarckian models used by students and their representations. In K. M. Fisher and M. Kibby, Editors, Knowledge Acquisition, Organization and Use in Biology, pp.65-77. New York, NY: Springer Verlag.

Lawson, A. E. & Thompson, L. D. (1988). Formal reasoning ability and misconceptions concerning genetics and natural selection. Journal of Research in Science Teaching, 25(9), 733-746.

Lerner, L.S. (2000). Good Science, Bad Science: Teaching Evolution in the States. Washington, DC: Thomas B. Fordham Foundation.

Mayr, E. (1982). The Growth of Biological Thought, Cambridge, MA: Harvard University Press.

Malthus, T.R. (1826). An Essay on the Principle of Population, as It Affects the Future Improvement of Society, 6th Edition London: Murray.

Moore, R. (2002). Do standards matter? How the quality of state standards relate to evolution instruction. The Science Teacher, 69(1), 49-51.

National Academy of Science. (1998). Teaching About Evolution and the Nature of Science. Washington, DC: National Academy Press.

National Association of Biology Teachers. (1995). Statement on teaching evolution. Retrieved August 27, 2002 from http//.www.nabt.org.

National Science Teachers Association. (1997 ). An NSTA position statement on the teaching of evolution. Journal of College Science Teaching, 27(1), 7-8.

Rudolph, J. L. & Stewart, J. (19(18). Evolution and the nature of science: on the historical discord and its implications for education Journal of Research in Science Teaching, 35(10), 1069-1089.

MURRAY JENSEN (msjensen@umn.edu) is Associate Professor in the Department of Postecondary Teaching and Learning, RANDY MOORE is Horace J. Morse-University of Minnesota Alumni Professor, JAY HATCH is Associate Professor of Biological Sciences, and LEON HSU is Associate Professor in the Department of Postsecondary Teaching and Learning, all at University of Minnesota, Minneapolis, MN 55455.
Figure 1. Scoring Rubric for Students' Answers to Questions about
Evolution.

Darwinian Component #1: KEY TERMS & CONCEPTS
Variation variation within a population
 genetic differences
There exists within every mutation in the genes/DNA
population variation between mutation as a source of variation
individuals and the origin of change due to a mutation
that variation is chance. There was a mutation.
 There was a change in the genes/DNA.

Darwinian Component #2: KEY TERMS & CONCEPTS
Genetics passed on to the next generation
 Something in the genes is passed to the
Organisms pass inheritable next generation.
information information Genes were passed on.
from one generation passed to their offspring
to the next. passing on genes
 The dead one's genes were not passed
 on.

Darwin Component #3: KEY TERMS & CONCEPTS
Differential Survival & limit in resources
Reproduction some survived, many died/survival
 of the fittest potential
 fertility/geometric reproductive rate

There occur in nature events The total population size usually
where some organisms die remains about the same. struggle for
and others survive. However, existence
overtime, population size fitness: the number of offspring
remains relatively stable. produced death/many died/some died/all
 died some survived
 enabled them to survive/live/eat/
 reproduce
 The food was limited (limits in natural
 resources).
 extinction

Darwinian Component #4: KEY TERMS & CONCEPTS
Change Over Time There were more of them than in the
 previous generation.
 more and more individuals with the
Over time, the percentage of trait/genes
a population that possesses changes in the percentage of
a specific trait increases in individuals within the population
frequency.This is the concept with specific traits or genes
of adaptation. (sometimes students use the word
 "dominant" to denote this" concept
 which is a common genetic/evolution
 misconception)
 changes to a population over time
 changes in the percentage of
 individuals with specific traits
 population genetics
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Author:Jensen, Murray; Moore, Randy; Hatch, Jay; Hsu, Leon
Publication:The American Biology Teacher
Geographic Code:1USA
Date:Sep 1, 2007
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