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Evolution of students' ideas about natural selection through a constructivist framework.

The concept of biological evolution within populations, or genetic change over time to populations, is a central principle of biological science; "Nothing in biology makes sense except in the light of evolution" (Dobzhansky, 1973). However, national polls show that over 45% of Americans do not accept the theory of evolution by natural selection (Quammen, 2004). Moreover, in the debate about whether or not evolution should be taught in schools, we have lost sight of what students really understand about the process of natural selection and its role in evolution.

Educating students about the process of evolution through natural selection is vitally important because not only is it the unifying theory of biological science, it is also widely regarded as difficult for students to fully comprehend (Sandoval, 2003). Anderson and colleagues (2002) describe alternative ideas and misconceptions about natural selection as highly resistant to change. Catley (2006) suggests that the educational emphasis on microevolutionary processes has left both teachers and students with a poor understanding of macroevolution and speciation.

To truly understand evolution, students need to understand other basic biological processes. Educational literature confirms that comprehension of evolution is made possible through the understanding of the individual concepts that comprise the theory (Passmore & Stewart, 2000). Even when students do grasp the basic idea of natural selection, the underlying concepts may be unclear (Kadury-Slezak, 2001). Many students also tend to view individual organisms as representative of entire populations and fail to recognize population variation as necessary for evolutionary change; thus students do not distinguish between individuals and species when describing selection (Greene, 1990; Hallden, 1988). Such typological thinking can lead to a belief that organisms have the power to change their traits in response to the environment, particularly when students fail to understand mechanisms of inheritance (Helm, 2002; Sandoval, 2003; Wood-Robinson, 1995).

Compounding the problem is that in many courses of study, students' experience with science is merely a survey of information without any meaningful exposure to the process that produced the information (Clough & Olson, 2004). This missing component of science education is evident in the public's lack of understanding about what constitutes a scientific theory (McComas, 2004). In science, a theory is an explanation based upon extensive testing that is well-supported by the accumulation of evidence. When students are not exposed to studies in the nature of science, they are not able to distinguish between a scientific theory and the vernacular usage of theory to mean a guess or an unsupported explanation (Backhus, 2004). This discrepancy between a scientific theory and a personal theory is of particular relevance to evolution education because one of the common misconceptions about evolution is that it is "just a theory."

Instruction that highlights the nature of scientific thought is the key to students' understanding about natural selection. Instruction in evolution must therefore focus also on the epistemic thinking that has led to the development of evolution theory as the best scientific explanation we have for the diversity of life on Earth. According to Sandoval (2003) such instruction should include scientific epistemological components like causal explanations, parsimony in developing conclusions, accounting for observations in explanations, and reliance on creativity. If students have a basic knowledge of the nature of science, their development of explanatory models can actually reconstruct the concept of natural selection (Passmore & Stewart, 2000). Conceptualization of the scientific process also helps students understand why scientists consider natural selection to be a strongly-supported theory and the best explanation for life's diversity (Backhus, 2004).

The challenge to teaching concepts such as natural selection through the process of inquiry is that oftentimes student beliefs drive the direction of the inquiry (Sandoval & Morrison, 2003) whereas the goal of instruction may be conceptual change of those beliefs. The gradual addition of new knowledge can help steer the inquiry while crafting new concepts or changing existing misconceptions. Strategies for conceptual change include active engagement with evidence, consideration of student learning needs, representation of the nature of science within the concepts under study, and a challenging curriculum (Tytler, 2002). These strategies reflect the practice of scientific investigation itself and can be particularly powerful for a complex concept such as natural selection. Geraedts and Boersma (2006) found that when students were engaged in guided reinvention of the development of Darwin's theory through a sequence of questions based on the logical nature of the theory, the majority of students developed Darwinian concepts of change over time.

A constructivist model provides a framework for effective teaching about natural selection by progressively adding concepts into the framework of existing knowledge. This model of instruction is particularly useful when the theory is used as an organizing principle for constructivist teaching and is presented as a framework for further investigation rather than an indisputable fact (Andersson & Wallin, 2006; Sandoval & Reiser, 2004). Cladistic analysis and other analytical tools used to reconstruct relationships and understand evolutionary history can also be powerful cognitive aids in promoting students' understanding of speciation (Catley, 2006).

Constructivist philosophy involves building new concepts into the ideas and beliefs already held by students. Constructivist learning represents the assimilation of new ideas into existing worldviews and the shifting of those worldviews to accommodate the new ideas (Brooks & Brooks, 1993). Teachers who use constructivism develop lessons that take students' previous conceptions into account and build new knowledge sequentially. Constructivist lessons account for both previous and upcoming content, and each lesson or idea builds upon previous ones. Constructivist teachers provide opportunities for students to collaborate and discuss ideas with one another, as such discussions are recognized as necessary for assimilation and accommodation. Constructivist learning thus involves a building of knowledge upon the foundation of concrete experiences both inside the classroom and in students' everyday experience.

In order to effectively develop curriculum for the teaching of evolutionary biology, it is important to know what students think and understand about natural selection. For this study, we surveyed 9th grade (freshman) general science and 12th grade (senior) biology students' knowledge and attitudes about natural selection before and after a constructivist sequence targeting specific concepts related to natural selection and the nature of scientific investigation. Our goal was to investigate whether students grasped not only the basic theory of natural selection, but also the underlying concepts that support the theory and are needed for a more thorough understanding of natural selection. We identified these fundamental concepts as (1) population variation, (2) mutation and the genetic basis for diversity, and (3) selective pressure in the environment.

* Methods

The Students

This study was conducted at the University Laboratory School (ULS) in Honolulu, Hawaii, which is a charter school and test ground for curriculum at the University of Hawaii's Curriculum Research and Development Group (CRDG). The ULS student population is selected by stratified lottery to represent a cross-section of the state's educational population. Thus, a range of ethnicities, socioeconomic groups, and ability levels are included in heterogeneous ULS classes. All students take the same curriculum and share a common educational background with their peers once they enter the school. We took advantage of a change in teaching staff and curriculum that provided a unique opportunity to compare the attitudes of seniors and freshmen who had not been previously exposed to formal instruction about evolution. We worked with freshmen in the Marine Science course (a general science course) and seniors in the Biology course. Each course was divided into two classes. The freshman course contained 52 students of equal sex distribution. The senior class contained 49 students. Because the senior class had a high level of absenteeism due to college visits, we were only able to collect data from 39 seniors (17 males and 22 females).

Students enter ULS in kindergarten, 6th, or 8th grade. The high school science course sequence from 9th to 12th grade is: Marine (General) Science, Physics, Chemistry, and Biology. ULS students who had taken Marine Science prior to the development of the natural selection unit described here had received lessons on classification and diversity without any explicit instruction in natural selection or evolutionary biology during their Marine Science experience. Thus, although the senior class in this study had taken more science courses, it had not previously received formal instruction on natural selection prior to the lessons presented during this study.

Instruction

After completing a pre-survey (described later), students took part in a constructivist unit on natural selection. Each lesson emphasized an aspect of natural selection theory and built upon the previous lessons. We did not develop this sequence to lead students through Darwin's reasoning as in some other evolutionary biology sequences (Geraedts & Boersma, 2006). Rather, we attempted to build a logical sequence of lessons and activities that provided for an increasingly complex and inclusive idea of natural selection as a mechanism for genetic change within populations over time.

[FIGURE 1 OMITTED]

The lesson sequence introduced concepts through laboratory activities, models, and simulations (Table 1). In alignment with constructivist learning philosophy, each lesson not only built on previous concepts but also connected to upcoming lessons. The laboratory activities were not used to demonstrate concepts that had already been introduced, but rather to elicit student questions that would lead to the discovery of those concepts. The simulations were designed to produce variable results and provide room for student interpretation and discussion about what their data meant. The simulations also provided concrete models that students could manipulate and experience directly. These simulations, which students could directly experience, were connected to real-world examples that students could not see directly in action. We emphasized the use of evidence to produce patterns and draw conclusions. Through the use of a constructivist strategy, in each new segment of the unit we emphasized continual building of evidence and application of knowledge learned in previous lessons. Readers of Darwin know that he approached the building of his theory in the same way.

Although both the freshman and senior level courses utilized the same basic sequence of lessons, we did make modifications to the sequence in response to student questions and to align to the curricular program. For example, in Marine Science, the unit was connected to a previous unit on fish diversity, and fish served as the prime example of natural selection in action. In Biology, a heavier emphasis was placed on the genetic aspects of the theory in connection to the course material on genetics.

The Surveys

Students were given surveys prior to and following the unit. The surveys were designed to gain information about students' understanding of natural selection processes as well as their attitudes about the theory (Appendix A). These surveys were administered to students anonymously, with each student given an alphanumeric code to enable paired comparisons of pre- and post-surveys.

The surveys consisted of three parts. The first part asked students to list the first three words they thought of when considering natural selection. We categorized these words based on the type of word selected. These categories were positive, negative, misconception, unrelated concept, target concept, word repeat (use of nature or selection or some similar variation), humans, evolution, intelligent design, Darwin, genetics, selective pressure, survival, and populations. Because some words fit more than one category, we recorded the percentage of total words listed in each category. We compared word choice within both grade levels pre- and post-instruction using two-sample, paired t-tests, and we compared between grade levels both prior to and following instruction using two-sample, unpaired t-tests.

[FIGURE 2 OMITTED]

In the second portion of the survey we asked students to choose all correct responses to statements about natural selection. We recorded the number of students choosing each response and compared changes in both grade levels and between grade levels using binomial distributions to identify which answers were selected by students at levels above or below expected levels of 50% if students were randomly guessing at answers.

The final portion of the survey included a series of questions with Likert-scale responses to content and attitude statements about natural selection. We compiled the responses for each question and compared these via two-sample, paired t-tests for each grade level pre- and post-instruction as well as between grade levels both before and after instruction using two-sample, unpaired t-tests.

* Results

Figure 1 shows the proportion of word types recorded by freshmen and seniors before and after instruction. Statistical analysis of word choices is summarized in Table 2. Prior to instruction, freshmen listed significantly fewer target concepts (18.3%) than did seniors (44.1%) in the word choice categories. Freshmen also listed significantly more words indicating misconceptions (5.2%) than the seniors (0.8%). Prior to instruction, the highest proportion of words recorded by freshmen were terms that repeated the idea of natural selection (20.9%), again at levels significantly higher than such terms were recorded by the seniors. For example, many freshmen used the words nature, natural, and selection. Conversely, the seniors recorded more words like evolution and Darwin (8.2% and 11.7% respectively). The seniors also listed significantly more words that identified ideas like survival (11.7%) and populations (5.8%).

Following instruction, the freshmen showed significant changes in eight categories of words listed compared to their choices prior to instruction, whereas the seniors showed significant changes in only one category. The seniors decreased the number of unrelated concepts they listed from 6% to 0, but otherwise did not show significant change in their word choice after instruction. Despite the emphasis on genetics in the ULS biology course, the seniors did not show a significant increase in terms related to the genetic basis of inheritance. The freshmen significantly decreased the proportion of words they listed that were misconceptions to 0 or repeat terms to 4.2%, and they also significantly decreased the number of times they listed evolution (0.6%). The freshmen also significantly increased their listing of target words to 60% and of specific target words related to populations (5.8%), selective pressures (19.2%), and genetic inheritance (16.7%). Only one student, a senior, mentioned intelligent design in both the pre- and post-surveys.

Both grade levels changed their attitudes about natural selection following instruction, as seen in Figure 2. In the statistical analysis of the attitude portion of the surveys (Table 3), freshmen significantly improved their attitudes about natural selection in response to all five statements. The seniors showed significant improvement in only one, "Natural selection is the best supported explanation for the diversity of life on Earth," with an average Likert response change from 3.0 to 3.4. However, prior to instruction, the freshmen had a significantly lower average response to the statement "Natural selection applies to all organisms on Earth," (3.0) compared to the seniors (3.4). Following instruction, freshmen had a significantly higher response to the statements "Natural selection helps explain why organisms look the way they do," and "Scientists need to consider natural selection when trying to solve problems," both with an average response of 3.5 in comparison to the senior response of 3.3 and 3.2, respectively.

Table 4 summarizes the percentage of students selecting each possible response to statements about natural selection. The associated binomial distribution statistics indicate when student responses were at non-random levels that would be expected if students were not simply guessing. When we asked students to identify accurate ideas about natural selection, the "don't know" response by freshmen overall dropped significantly following instruction. Prior to instruction, an average of 33.3% of freshmen responded "don't know" to the three statements provided. After instruction, an average of 2% of freshmen responded "don't know." This category did not change for seniors, as only two of them selected it as an initial response for any of the three statements. For the statement, "Natural selection applies to ..." (Figure 3a) both groups increased in their response to the target answer of populations (29% for freshmen, 13% for seniors). For both groups, following instruction, the binomial distribution statistic was significant, indicating choice above levels associated with random guessing. The freshmen increased their selection of individuals as the unit on which natural selection operates by 9%, while the seniors decreased this selection by 7%. For the statement about the measure of success in nature (Figure 3b), the freshmen had a range of responses prior to instruction, but they significantly increased their choice of surviving offspring as the accurate response by 36% with an associated significant binomial statistic. There was no significant change for seniors in response to this statement. In response to the statement about the source of change in organisms (Figure 3c), both groups significantly increased their response of random mutation. Freshmen increased this choice by 45% and seniors by 25% and the associated binomial distribution statistics indicated a choice level significantly above what would be expected in a random guess. However, both groups also retained the misconception about an organism's ability to modify itself, indicating both before and after instruction that organisms can change by learning to modify their bodies. Before instruction, 52% of freshmen and 53% of seniors selected this option, and after instruction 46% of freshmen and 48% of seniors did so. The binomial distribution statistics for each of these values were not significant, and did not indicate a clear change in knowledge about this particular aspect of natural selection.

* Discussion

Our results suggest that while the seniors had more time to gain information about natural selection, they also had more time to solidify their conceptions. Even though the seniors had not previously received explicit instruction in natural selection earlier in their high school career, it appears that they picked up many concepts along the way. The freshmen, in comparison, had larger percentages of changes in both their attitudes about natural selection and their content knowledge. Although the seniors began ahead of the freshmen, the surveyed level of content knowledge in the freshmen improved beyond the demonstrated level of the seniors following instruction. When we examined attitudes about natural selection in response to a series of statements, we found that seniors and fresh-men had a mixed range of positive responses prior to instruction. Following instruction, however, the freshmen again consistently outstripped the seniors with higher levels of positive response to all statements about natural selection. Freshmen also decreased their listing of replacement words like natural and selection as well as their use of the general term evolution in favor of more specific ideas. This evidence supports the suggestion that, in order to avoid misconceptions and allow for full development of inquiry, natural selection should be taught as early in the high school progression as possible.

[FIGURE 3a OMITTED]

[FIGURE 3b OMITTED]

One misconception identified and retained by both groups is that "Organisms learn to change their bodies over time." The number of students selecting this response did not change in either group after instruction. Although both freshmen and seniors increased their response to the accurate "random mutation" option, many were those students previously selecting "don't know." Thus, our data suggests that the students who entered into instruction with a Lamarckian idea of evolution retained it. Previous studies have found that students tend to view organisms conceptually as biological types that change directly in response to environmental pressure rather than through random mutation that introduces variation into the population of organisms (Shtulman, 2006; Wood-Robinson, 1995). The failure of students to change ideas about natural selection being the best-supported explanation for diversity may also be a result of student ideas about biological types.

The students' retention of the Lamarckian misconception highlights a gap in our sequence of instruction and identifies a missing link for students attempting to form a cohesive understanding of natural selection. One aspect of instruction that may be responsible for reinforcing Lamarckian misconceptions in students is that the freshman instructor placed continued emphasis upon species change in response to environmental pressures. This phrasing was used in part because the freshman unit focused on fish (whereas the senior unit focused on genes). This emphasis could have reinforced the idea that organisms do change their bodies purposefully in response to the environment, rather than the more accurate idea that the environment may select one change over another, but that change itself is solely the result of mutations to genes. Although students did gain the idea that change occurs through mutation, they seem to have attached the mutagenic changes to the idea that organisms can direct that change themselves.

Freshmen gained another misconception through instruction; they significantly increased their choice of "individuals" as a response to statements about the level at which natural selection acts. The confusion among students about natural selection acting on individuals or populations is well-documented (Andersson & Wallin, 2006; Greene, 1990;Hallden, 1988; Shtulman, 2006). Student confusion is often introduced when teachers alternate between levels of organization ranging from genes to species without distinguishing clearly between them (Andersson & Wallin, 2006). In this case, the leap from microevolutionary to macroevolutionary processes was perhaps too great for students to bridge, which has been suggested to be a common problem in evolution education (Catley, 2006). The instructional sequence we used might benefit from an additional lesson to clarify the genetic basis of variation in populations. The increased emphasis on genetics as a mechanism for variation can also help clarify the misconception of purposeful change by organisms in response to environmental pressure.

[FIGURE 3c OMITTED]

Although both instructors made some modification to the lesson sequence to meet their individual needs, both freshmen and seniors significantly increased their positive response to the statement, "Natural selection is the best supported explanation for the diversity of life on Earth." For the seniors, this was the only statement for which they significantly increased their positive response. Given that the primary goal of instruction was to increase understanding about, and acceptance of, natural selection as the scientific theory that best explains diversity, this result is particularly gratifying.

We undertook this study in part to find out how our students viewed natural selection. Given the well-publicized efforts to implement non-scientific curricula (such as intelligent design) in schools, we anticipated a higher level of responses related to these ideas than we received. In the word choice portion of the survey, only one student referred to any form of non-natural intervention related to species diversity. Student responses to statements about natural selection that ascribed change to supernatural forces, or indicated natural selection did not apply to any organisms or to humans specifically were low in both groups. For our students in Hawaii, at least, this result implies that students are ready to accept natural selection, and that suggestions to "teach the controversy" might be counterproductive by introducing a non-scientific idea that is not necessarily already present in the students' worldview.
Appendix A. Survey

Write down the first three words you think of for natural selection.

Circle all answers you think are accurate about each statement.

Natural selection applies to ...

individuals populations everything
 but humans
The measure of success in nature is ...

age enemies mating
reached killed opportunities

Changes result from ...

organisms random genetic
learn to modify mutation material is
their bodies passed on

Natural selection applies to ...

individuals all organisms nothing

The measure of success in nature is ...

age surviving food
reached offspring gathered

Changes result from ...

organisms loss of body supernatural
learn to modify parts intervention
their bodies

Natural selection applies to ...

individuals I don't know

The measure of success in nature is ...

age I don't know
reached

Changes result from ...

organisms I don't know
learn to modify
their bodies

Choose the response that best represents how you feel about each
statement.

Natural selection is the best supported explanation for
the diversity of life on Earth.

strongly strongly
disagree disagree unsure agree agree

1 2 3 4 5

Natural selection helps explain why organisms look the
way they do.

strongly strongly
disagree disagree unsure agree agree

1 2 3 4 5

Natural selection applies to all organisms on Earth.

strongly strongly
disagree disagree unsure agree agree

1 2 3 4 5

Natural selection affects humans.

strongly strongly
disagree disagree unsure agree agree

1 2 3 4 5

Scientists need to consider natural selection when trying
to solve problems.

strongly
disagree disagree unsure agree agree

1 2 3 4 5


References

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

Andersson, B. & Wallin, A. (2006). On developing content-oriented theories, taking biological evolution as an example. International Journal of Science Education, 28(6), 673-695.

Backhus, D. (2004). It's not lust a theory. In R. Bybee (Editor), Evolution in Perspective (pp. 37-42). Arlington, VA: NSTA press.

Brooks, J.G. & Brooks, M.G. (1993). The Case for Constructivist Classrooms, Association for Alexandria, VA: Supervision & Curriculum Development.

Catley, K.M. (2006). Darwin's missing link: A novel paradigm for evolution education. Science Education, 90, 767-783.

Clough, M. & Olson, J. (2004). The nature of science: Always part of the science story. The Science Teacher, 71 (9), 28-31.

Dobzhansky, T. 1973. Nothing in biology makes sense except in the light of evolution. The American Biology Teacher, 35(3), 125-129.

Geraedts, C.L. & Boersma, K.T. (2006). Reinventing natural selection. International Journal of Science Education, 28(8), 843-870.

Greene, E.D. (1990). The logic of university students' misunderstanding of natural selection. Journal of Research in Science Teaching, 27, 875-885.

Hallden, O. (1988). The evolution of the species: Pupil perspectives and school perspectives. International Journal of Science Education, 10(5), 541-552.

Heim, W.G. (2002). Natural selection among playing cards. The American Biology Teacher, 64(4), 276-278.

Kadury-Slezak, M. & Dreyfus, A. (2001). Science for all: Making science accessible to all. Science & Technology Education: Preparing Future Citizens. Proceedings of the IOSTE Symposium in Southern Europe. Cyprus. April 29-May 2, 2001.

McComas, W. (2004). Keys to teaching the nature of science. The Science Teacher, 71(9), 24-27.

Passmore, C. & Stewart, J. (2000). A Course in Evolutionary Biology: Engaging Students in the "Practice" of Evolution. Research Report. Madison, WI: Wisconsin University National Center for Improving Student Learning and Achievement in Math and Science.

Quammen, D. (2004). Darwin's big idea. National Geographic, 206(5), 2-35.

Sandoval, W.A. (2003). Conceptual and epistemic aspects of student scientific explanations. The Journal of the Learning Sciences, 12(1), 5-51.

Sandoval, W.A. & Morrison, K. (2003). High school student ideas about theory and theory change after a biological inquiry unit. Journal of Research in Science Teaching, 40(4), 364-392.

Sandoval, W.A. & Reiser, BJ. (2004.). Explanation-driven inquiry: Integrating conceptual and epistemic scaffolds for scientific inquiry. Science Education, 88, 345-372.

Shtulman, A. (2006). Qualitative differences between naive and scientific theories of evolution. Cognitive Psychology, 52, 170-194.

Tytler, R. (2002). Teaching for understanding in science: Constructivist/conceptual change teaching approaches. Australian Science and Technology Journal, 48(4), 30-35.

Wood-Robinson, C. (1995). Children's biological ideas: Knowledge about ecology, inheritance, and evolution. In S.M. Glynn & R. Druitt (Editors), Learning Science in Schools: Research Reforming Practice. Mahwah, NJ: Laurence Erlbaum Associates, Inc.

BIO

ERIN BAUMGARTNER is Assistant Professor of Biology, Western Oregon University, Monmouth, OR 97361; e-mail: baumgartner@wou.edu. KINESA DUNCAN is Assistant Professor of Education, Curriculum Research & Development Group, University of Hawaii-Manoa, Honolulu, HI 96822; e-mail: Kanesa@Hawaii.edu.
Table 1. Constructivist activities used to teach natural selection.

CONCEPT ACTIVITY CONSTRUCTIVIST
 CONNECTIONS

Taxonomy Students classify Builds toward: Elicits
 different organisms question, Why are
Common ancestry and highlight the there so many kinds of
 unique features held organisms. Highlights
 in common at each features that
 level. demonstrate points of
 divergence and common
 ancestry.

Genetic basis of Students model Builds on:
inheritance transcription errors Demonstrates mechanism
 through "telephone" for change and
 game. diversity.

Mutation Recording the message Builds toward:
 meaning at various Foundation for
 points in chain microevolution model
 illustrates change by providing mechanism
 through additive for antibiotic
 mutations. resistance.

 Student "mutagens"
 purposefully change
 message.

Microevolution Students model Builds on:
 microevolution in a Demonstrates change in
 population of population structure
 "bacteria" (colored following mutation.
 paper clips),

Population variation Dice rolls simulate Builds toward:
 variable probability Introduces idea of
Random process of death in wild type selective pressure and
 and resistant how traits are
 bacteria. Students selected for or
 graph simulated against.
 population dynamics of
 both types through
 multiple courses of
 antibiotics.

Selective pressure Student "predators" Builds on:
on populations hunt for red bean and Demonstrates how
 split pea "prey" in a selective pressure
 rice environment using operates when one
 chopsticks. Students feature increases
 graph populations of likelihood of survival
 small, hidden peas to to reproduction in the
 large visible beans environment of the
 over multiple organism.
 generations.

 Students repeat Builds toward:
 activity with black Population variation
 and white beans in can lead to speciation
 white or wild (black) when selective
 rice environments. pressures in different
 environments lead to
 selection for
 different traits.

Speciation Students match Builds on: Examination
 marsupials and of evidence to support
 placentals to identify how can selection for
 how selective pressure traits in different
 can modify ancestral environments can lead
 type to fill a range to diversity of
 of niches. organisms.

Adaptive radiation Students make Reinforcement of
 adaptations to genetic inheritance
 styrofoam ball through demonstration
 "ancestral type" of similar selective
 organism for different forces on marsupials
 environments. and placentals.

 Multiple students Modeling adaptive
 adapt organisms in radiation from a
 same environment to common ancestor to
 demonstrate random diversity of species
 nature of mutation depending on random
 and diversity of mutation and
 adaptations to same environmental
 habitat. pressures.

Table 2. Differences in word choice within and between class
before and after instruction. Differences were compared pre-and
post-instruction using two-sample, paired t-tests within grade
levels and unpaired t-tests between grade levels. Significance at
p [less than or equal to] 0.05. X refers to no selection of words
in the category, eliminating the basis for statistical
comparison.

Word Type Statistical Pre-Instruction Post-Instruction
 Value Freshman-Senior Freshman-Senior
 Comparison Comparison

Positive Df 97 90
 t -3.038 -2.690
 p 0.002 0.004

Negative Df 97 90
 t -2.412 -4.144
 p 0.009 [less than or equal
 to] 0.001

Unrelated Df 97 90
 t 1.286 1.869
 p 0.101 0.032

Target Df 97 90
 t -3.339 2.235
 p [less than or equal 0.014
 to] 0.001

Misconception Df 97 X
 t 1.798 X
 p 0.037 X

Repeat term Df 97 90
 t 2.82 -0.436
 p 0.003 0.330

Humans Df 97 90
 t -0.47 -1.636
 p 0.319 0.052

Evolution Df 97 90
 t -1.471 -3.29
 p 0.072 [less than or equal
 to] 0.001

Darwin Df 97 90
 t -2.496 -2.699
 p 0.007 0.004

Genetics Df 97 90
 t -1.14 1.56
 p 0.128 0.061

Selective Df 97 90
pressures t 0.970 3.808
 p 0.167 [less than or equal
 to] 0.001

Survival Df 97 90
 t -2.185 -3.810
 p 0.016 [less than or equal
 to] 0.001

Populations Df 97 90
 t -2.131 -0.023
 p 0.018 0.049

Word Type Statistical Freshman Pre-
 Value Post Instruction
 Comparison

Positive Df 101
 t -0.786
 p 0.217

Negative Df 101
 t 1.596
 p 0.057

Unrelated Df 101
 t 1.309
 p 0.097

Target Df 101
 t -6.739
 p [less than or equal
 to] 0.001

Misconception Df 101
 t 2.24
 p 0.014

Repeat term Df 101
 t 4.756
 p [less than or equal
 to] 0.001

Humans Df 101
 t 1.785
 p 0.039

Evolution Df 101
 t 2.003
 p 0.024

Darwin Df 101
 t 0.759
 p 0.224

Genetics Df 101
 t -4.01
 p [less than or equal
 to] 0.001

Selective Df 101
pressures t -4.11
 p [less than or equal
 to] 0.001

Survival Df 101
 t 1.072
 p 1.429

Populations Df 101
 t -3.235
 p [less than or equal
 to] 0.001

Word Type Statistical Senior
 Value Pre-Post Instruction
 Comparison

Positive Df 86
 t -7.050
 p 0.241

Negative Df 86
 t -0.389
 p 0.349

Unrelated Df 86
 t 1.670
 p 0.049

Target Df 86
 t -0.863
 p 0.195

Misconception Df 86
 t 0.912
 p 0.182

Repeat term Df 86
 t 1.23
 p 0.111

Humans Df 86
 t 0.612
 p 0.271

Evolution Df 86
 t 0.046
 p 0.481

Darwin Df 86
 t 0.432
 p 0.333

Genetics Df 86
 t -1.322
 p 0.094

Selective Df X
pressures t X
 p X

Survival Df 86
 t -0.579
 p 0.282

Populations Df 86
 t -1.292
 p 0.010

Table 3. Attitude change in freshmen and seniors before and after
instruction. Students' Likert-scale responses (1 = strongly
disagree; 5 = strongly agree) were compared via paired two-
sample t-tests within grade levels and via unpaired two-sample
t-tests between grade levels. Significance at p [less than or
equal to] 0.05.

Statement Statistical Pre-Instruction
 Value Freshmen-Senior
 Comparison

Natural selection is the average -0.18
best supported explanation response
for the diversity of change
life on Earth. Df 88
 T 1.338
 P 0.092

Natural selection helps Delta -0.11
explain why organisms Df 89
look the way they do. T 0.850
 P 0.199

Natural selection applies average 0.39
to all organisms on response
Earth. change
 Df 89
 T -2.806
 P 0.003

Natural selection affects average 0.14
humans. response
 change
 Df 89
 T -1.007
 P 0.158

Scientists need to average
consider natural response -0.05
selection when trying to change
solve problems. Df 89
 T 0.338
 P 0.368

Statement Statistical Post-Instruction
 Value Freshmen-Senior
 Comparison

Natural selection is the average -0.09
best supported explanation response
for the diversity of change
life on Earth. Df 90
 T 0.760
 P 0.224

Natural selection helps Delta -0.28
explain why organisms Df 90
look the way they do. T 2.460
 P 0.007

Natural selection applies average -0.05
to all organisms on response
Earth. change
 Df 90
 T 0.393
 P 0.347

Natural selection affects average -0.18
humans. response
 change
 Df 90
 T 1.485
 P 0.704

Scientists need to average
consider natural response -0.26
selection when trying to change
solve problems. Df 90
 T 2.344
 P 0.011

Statement Statistical Freshman Pre-
 Value Post Instruction
 Comparison

Natural selection is the average 0.28
best supported explanation response
for the diversity of change
life on Earth. Df 101
 T -2.77
 P 0.003

Natural selection helps Delta 0.32
explain why organisms Df 101
look the way they do. T -2.906
 P 0.002

Natural selection applies average 0.46
to all organisms on response
Earth. change
 Df 101
 T -3.766
 P [less than or
 equal to] <0.001

Natural selection affects average 0.35
humans. response
 change
 Df 101
 T -2.879
 P 0.002

Scientists need to average
consider natural response 0.36
selection when trying to change
solve problems. Df 101
 T -3.306
 P [less than or
 equal to] <0.001

Statement Statistical Senior Pre-
 Value Post Instruction
 Comparison

Natural selection is the average 0.38
best supported explanation response
for the diversity of change
life on Earth. Df 78
 T -2.49
 P 0.007

Natural selection helps Delta 0.15
explain why organisms Df 78
look the way they do. T -1.11
 P 0.13

Natural selection applies average 0.03
to all organisms on response
Earth. change
 Df 78
 T -0.175
 P 0.430

Natural selection affects average 0.02
humans. response
 change
 Df 78
 T -0.176
 P 0.430

Scientists need to average
consider natural response 0.15
selection when trying to change
solve problems. Df 78
 T -1.011
 P 0.157

Table 4. Responses to statements about NS selected by students
before and after instruction. The % columns indicate the
percentage of students choosing each response. The binary
statistic indicates p values for tests of binomial distributions
used to identify which answers were selected by students at
levels above or below expected levels of 50% if students were
randomly guessing at answers. Significance at p less than or
equal to] 0.05. * indicates ideas supported by NS theory.

Concept Answers % Freshmen
 Choosing
 Pre-Instruction
 (binary statistic)

Natural selection individuals 16
applies to: [less than or equal
 to] 0.001

 populations * 44
 -0.079

 everything but 2
 humans [less than or equal
 to] 0.001

 all organisms * 66
 -0.009

 nothing 0
 [less than or equal
 to] 0.001

 don't know 28
 [less than or equal
 to] 0.001

The measure age reached 20
of success in [less than or equal
nature is: to] 0.001

 enemies killed 10
 [less than or equal
 to] 0.001

 mating opportunities 32
 -0.004

 surviving off-spring * 58
 -0.060

 food gathered 22
 [less than or equal
 to] 0.001

 don't know 42
 -0.060

Changes to organisms learn to 52
organisms modify parts -0.108
result from:
 random mutation * 30
 -0.002

 genetic material 36
 passed on * -0.016

 parts lost 12
 [less than or equal
 to] 0.001

 supernatural 8
 [less than or equal
 to] 0.001

 don't know 30
 [less than or equal
 to] 0.001

Concept Answers % Freshmen
 Choosing
 Post-Instruction
 (binary statistic)

Natural selection individuals 25
applies to: [less than or equal
 to] 0.001

 populations * 73
 [less than or equal
 to] 0.001

 everything but 0
 humans [less than or equal
 to] 0.001

 all organisms * 71
 [less than or equal
 to] 0.001

 nothing 0
 [less than or equal
 to] 0.001

 don't know 0
 [less than or equal
 to] 0.001

The measure age reached 6
of success in [less than or equal
nature is: to] 0.001

 enemies killed 2
 [less than or equal
 to] 0.001

 mating opportunities 15
 [less than or equal
 to] 0.001

 surviving off-spring * 96
 [less than or equal
 to] 0.001

 food gathered 2
 [less than or equal
 to] 0.001

 don't know 2
 [less than or equal
 to] 0.001

Changes to organisms learn to 46
organisms modify parts 0.102
result from:
 random mutation * 75
 [less than or equal
 to] 0.001

 genetic material 48
 passed on * -0.110

 parts lost 10
 [less than or equal
 to] 0.001

 supernatural 2
 [less than or equal
 to] 0.001

 don't know 4
 [less than or equal
 to] 0.001

Concept Answers % Seniors Choosing
 Pre-Instruction
 (binary statistic)

Natural selection individuals 45
applies to: -0.113

 populations * 53
 -0.113

 everything but 10
 humans [less than or equal
 to] 0.001

 all organisms * 88
 [less than or equal
 to] 0.001

 nothing 0
 [less than or equal
 to] 0.001

 don't know 3
 [less than or equal
 to] 0.001

The measure age reached 35
of success in -0.027
nature is:

 enemies killed 15
 [less than or equal
 to] 0.001

 mating opportunities 25
 [less than or equal
 to] 0.001

 surviving off-spring * 85
 [less than or equal
 to] 0.001

 food gathered 28
 -0.003

 don't know 13
 [less than or equal
 to] 0.001

Changes to organisms learn to 53
organisms modify parts -0.113
result from:
 random mutation * 50
 -0.125

 genetic material 53
 passed on * -0.113

 parts lost 10
 [less than or equal
 to] 0.001

 supernatural 13
 [less than or equal
 to] 0.001

 don't know 10
 [less than or equal
 to] 0.001

Concept Answers % Seniors Choosing
 Post-Instruction
 (binary statistic)

Natural selection individuals 38
applies to: -0.046

 populations * 60
 -0.046

 everything but 3
 humans [less than or equal
 to] 0.001

 all organisms * 78
 [less than or equal
 to] 0.001

 nothing 0
 [less than or equal
 to] 0.001

 don't know 0
 [less than or equal
 to] 0.001

The measure age reached 28
of success in -0.003
nature is:

 enemies killed 13
 [less than or equal
 to] 0.001

 mating opportunities 38
 -0.046

 surviving off-spring * 90
 [less than or equal
 to] 0.001

 food gathered 13
 [less than or equal
 to] 0.001

 don't know 3
 [less than or equal
 to] 0.001

Changes to organisms learn to 48
organisms modify parts -0.125
result from:
 random mutation * 75
 -0.004

 genetic material 85
 passed on * [less than or equal
 to] 0.001

 parts lost 8
 [less than or equal
 to] 0.001

 supernatural 8
 [less than or equal
 to] 0.001

 don't know 0
 [less than or equal
 to] 0.001
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Author:Baumgartner, Erin; Duncan, Kanesa
Publication:The American Biology Teacher
Article Type:Report
Geographic Code:1USA
Date:Apr 1, 2009
Words:6746
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