A Tree-Thinking Curriculum For Introductory Biology
J. Phil Gibson & Mariëlle Hoefnagels
Department of Botany & Microbiology, Department of Zoology, University of Oklahoma, Norman, OK 73019
Conclusions
Tree-Thinking
Since Darwin first sketched his concept of evolution as a tree
diagram in Notebook B, phylogenetic trees have become important
graphical representations of evolutionary hypotheses, patterns,
and history. Tree-thinking links understanding evolution with how
it is represented in phylogenetic diagrams. It has been suggested
that integrating tree-thinking into introductory biology curricula may
help students better understand evolution.1,2,3,6,10 Our study tests
whether an introductory biology curriculum organized around
a central theme of tree-thinking will increase understanding
and acceptance of evolution as a scientific theory in
introductory biology students. We expect that engaging
students in active learning experiences that involve treethinking across hierarchical levels will increase their
acceptance and understanding of the scientific basis of
evolution.
Materials & Methods
Curriculum – The study focuses on BIOL 1134 (Evolution,
Ecology, and Diversity) a required course for botany, microbiology,
and zoology majors. We compared a semester using a Standard
Curriculum to three semesters using a Tree-Thinking
Curriculum. As shown below, the Tree-Thinking Curriculum starts
by teaching basic concepts of genetics followed by inheritance
and pedigrees (noncontroversial topics students understand and
readily accept). Next, evolutionary theory is presented in modules
that demonstrate fundamental principles and concepts. Modules
at this stage also basic teach techniques for phylogeny
construction using various types of data and interpretation of
phylogenetic trees as an extension of pedigree concepts. This is
followed opportunities to apply tree-thinking concepts and skills to
address different organismal and ecological questions.
Tree-Thinking Curriculum
DNA & Genetics
Assessment – Curricula were assessed and compared by pre- and
post-testing using the Measure of Acceptance of Theory of Evolution
(MATE) 12 a 20-item, Likert-scale instrument (scores range from 0
100). In F09, S10, and F10 students completed a Tree Reading
Assessment (TRA) containing 6 multiple choice and short answer
questions about phylogenetic trees and their interpretation (similar to
the Test Your Tree Thinking questions) to measure tree-thinking
skills.3,10 In S11, TRA was replaced by a 14 question (28 point) Tree
Thinking Concept Inventory8. Average normalized gain was calculated
for MATE (GMATE), TRA (GTRA), and TTCI (GTTCI).7 Pre- and post
MATE, TRA, and TTCI scores were compared via Wilcoxon Signed
Ranks Test, and Gain compared with a Kruskal-Wallace Test.
Students initially showed poor understanding of how time, character
change and relatedness are represented in phylogenetic trees.
However, they could identify common ancestors. These problems
were generally corrected under both curricula with notable
improvement for students in the Tree-Thinking Curriculum.
GMATE was significantly higher for the Tree-Thinking Curriculum than
the Standard Curriculum (Fig. 3). GTRA was slightly higher for the
Tree-Thinking Curriculum but not significantly different from the
Standard Curriculum. All Gain values were significantly greater than
zero except for MATE in the Standard Curriculum.
100.0
*
Results
Median MATE post-test scores were greater than pre-test scores in all
Tree-Thinking Curriculum semesters but were not in the Standard
Curriculum (Fig.1). Higher MATE post-test scores were primarily due
to higher scores on questions probing students’ understanding of the
acceptance of by scientists and understanding of the scientific data
supporting evolution. TRA post-test scores increased significantly
under both curricula, but did not differ significantly between curricula
(Fig. 2). Mean TTCI post-test scores (7.22) were significantly greater
(p < 0.001) than pre-test scores (20.60).
*
*
80.0
60.0
40.0
20.0
Test Your Tree-Thinking
Tree-thinking quizzes identify specific misconceptions and deficient
skills that can be targeted to improve evolution education.3,10
0.0
F09 pre
F09 post
S10 pre
S10 post
F10 pre
F10 post
S11 pre
S11 post
Figure 1. Quartile distribution and mean () MATE scores for
Standard and Tree-thinking curricula across 4 semesters. * indicates
significantly different median (p < 0.05) between pre and post scores.
1. In diagram A, are lizards more A
closely related to frogs or humans?
3. What does the letter x indicate?
B
Figure 2. Mean TRA scores for Standard and Tree-thinking curricula.
4. Are humans equally related to
frogs in both diagram A and B?
1
Phylogenetics
Concepts & Mechanisms
Read & Construct Trees
Application
(Biodiversity
surveys, adaptations,
speciation etc.)
Normailized Gain
TRA/TTCI
Evolution
Literature
1Alters,
2. In diagram A, are fish more
closely related to frogs or mice? In
B, are fish more closely related to
frogs or lizards.
Inheritance &
Pedigrees
The data indicate a significant increase in student acceptance of
evolution under the Tree-Thinking curriculum. In the four semesters
we have studied, median MATE scores at the beginning of the
introductory course are at the lower end of the high acceptance of
evolution category, and, after completing the Tree-Thinking curriculum,
scores are in the middle of the high level of acceptance category. TRA &
TTCI results indicate students improved in their ability to read and
understand phylogenetic tree diagrams in terms of the significance of
common ancestry and evolution. Students initially know what a common
ancestor is, but the Tree-Thinking curriculum helps students understand
what a common ancestor means. Combined with the MATE scores, the
results suggest there is increased understanding of the meaning,
content, and significance of phylogenetic trees in the Tree-Thinking
curriculum Thus, the Tree-Thinking modules we use appear to help
students correct common misconceptions about evolution11 and develop
their understanding of the meaning of common ancestors and how that
relates to phylogenetic interpretation. They also better understand the
significance of genetic, structural, ecological, and all other forms of
biological data supporting evolution. Preliminary analysis of responses
to questions in the MATE instrument indicates the tree-thinking
approach improves student understanding of the scientific data that form
the foundation supporting evolutionary theory. Further analysis of these
data and data from instruments evaluating introductory-level students’
prior understanding of genetics and evolution and other facets of their
science background will provide additional insights on how TreeThinking shapes and improves student learning of biology in general and
evolution in particular. Thus, our results to data are encouraging and
suggest further study and implementation of the Tree-Thinking
approach.
5. Assume the common ancestor
had a long tail, ear flaps, external
testes, and fixed claws. If all
evolutionary changes in these
traits are shown in the tree at the
right, what traits does a sea lion
have?
MATE
0.8
0.6
B.J. and C.E. Nelson. 2002. Perspective: Teaching evolution in higher education.
Evolution 56: 1891-1901.
2Baum, D. A., and S. Offner. 2008. Phylogenies and tree-thinking. The American Biology
Teacher 70: 222-229.
3Baum, D. A., S. D. Smith, and S. S. Donovan. 2005. Evolution. The tree-thinking
challenge. Science 310: 979-980.
4Bishop, B. A., and C. W. Anderson. 1990. Student conceptions of natural-selection and its
role in evolution. Journal of Research in Science Teaching 27: 415-427.
5Dobzhansky, T. 1973. Nothing in biology makes sense except in the light of evolution.
American Biology Teacher 35: 125-129.
6Gregory, T. R. 2008. Understanding evolutionary trees. Evolution Education Outreach
1:121-137.
7Hake, R. R. 2002. Lessons from the physics education reform effort. Conservation
Ecology, 28.
8Halverson Tree-Thinking Concept Inventory
9Kalinowski,S.T., M.J. Leonard, & T.M. Andrews. 2010. Nothing in evolution makes sense
except in the light of DNA. CBE Life Science Education 9(2): 87-97
10Meir, E., J. Perry, J. C. Herron, and J. Kingsolver. 2007. College students’
misconceptions about evolutionary trees. American Biology Teacher 69: 71-76.
11Nehm, R. H., and L. Reilly. 2007. Biology majors' knowledge and misconceptions of
natural selection. Bioscience 57: 263-272.
12Rutledge, M. L. K. C. Sadler. 2007. Reliability of the Measure of Acceptance of the
Theory of Evolution (MATE) instrument with university students. The American Biology
Teacher 69: 332-335.
13Society of Systematic Biologists. 2002. http://systbiol.org/
0.4
Acknowledgements
0.2
0
F09
Answers: 1. Humans, they share a more recent common ancestor. 2. Equally related to all in both
diagrams via same shared common ancestor (y). 3. X is the last common ancestor to frogs, lizards,
mice, & humans. 4. Yes. the relationships in both diagrams are the same for all taxa. 5. Short tail,
ear flaps, abdominal testes, & fixed claws.
5
evolution. ”
S10
F10
S11
-0.2
Curriculum
Research supported by National Science Foundation DUE #0940835,
The University of Oklahoma College of Arts and Sciences, The
Department of Botany and Microbiology, and The Department of
Zoology. Thanks to M. Jones, J. Cooper, S. Rhodes, A. Makowicz, C.
Poindexter, M. Gibson, D. Washecheck. Research conducted under
University of Oklahoma IRB #12682
Figure 3. Normalized learning gain for MATE and TRA/TTCI.
“Nothing in biology makes sense except in the light of
“Nothing in evolution makes sense except in the light of
9
“Nothing in evolution makes sense except in the light of DNA. ”
13
phylogeny. ”