Running head: UNDERSTANDING EVOLUTION
1
Understanding Evolution:
Why is it so hard, and what can educators do?
Ruth-Decker Chaney
Vanderbilt UniversityAbstract
This paper is a discussion of the intuitive biological thought processes that interfere with
the understanding of evolution, mainly essentialism and teleology. I compare the aspects of
these thought processes with Darwin’s logic progression for his conclusion of the mechanism of
evolution, natural selection, as stated in Mayr (1982). I also include the applicable parts of the
Evolutionary Synthesis (Futuyma, 2005). There are teaching recommendations suggested by the
literature in this paper as well as a list of resources available to the public.
Understanding Evolution: Why is it so hard and what can educators do?
Evolution is not always taught explicitly. For example, I worked for the biology
department at Duke University as a Teaching Assistant (January 2006 to May 2007 [three
semesters]) for the Organismal Diversity course, an introductory course and required for a
biology major and minor. It was the unofficial evolution course, according to one of the
Running head: UNDERSTANDING EVOLUTION
2
professors for whom I worked. Evolutionary concepts were not covered; it was expected that the
students would come to the understand evolution from seeing the broad diversity of life on the
planet. Most students still demonstrated basic misconceptions, which I refer to as “intuitive
biological thought processes” in this paper, of how evolution worked that counter scientific
understanding. One reason this occurred was because the students were too focused on
memorizing the details of the organisms instead of taking in the whole picture of life on earth.
This approach that Duke Biology, which was ranked the top graduate program in evolutionary
biology at that time, used at that time demonstrated the disconnect that exists between scientists
and the general public. As Bishop and Anderson (1990) identified in their research, the concepts
of evolution by natural selection are very difficult to comprehend, and many biologists do not
acknowledge that fact.
Understanding biological evolution is extremely important for basic scientific literacy in
today’s society. Being able to make informed decisions about issues that effect the quality of life
in the United States and around the world is important. Evolution is involved with everything
concerning biology, as geneticist Theodosius Dobzhansky presented a paper at the 1972 National
Association of Biology Teachers Convention titled “nothing in biology makes sense except in
the light of evolution” (1973, p. 125). Advances in medicine, e.g., the development of new
vaccines and new antibiotics, are necessary because of evolution of viruses and bacteria.
Increases in pesticide use in the agricultural sector influence the increases of proportions of
pesticide-resistant individuals in populations of targeted pests. The monoculture approach in
industrial farming, which means that all of the crop of interest is or almost genetically identical,
puts the food supply at risk in cases of infestation.
I focus this paper on the understanding of evolution, not acceptance (often referred to as
Running head: UNDERSTANDING EVOLUTION
3
“belief”1 [The National Center for Science Education promotes the use of the word “acceptance”
instead of “belief” (Scott, 2009)]). Understanding, as Smith and Siegal (2004, p. 533) states, is
“recognizing the key principles and their implications” of a scientific theory. Acceptance, on the
other hand, is “endorsing . . . [a] theory as ‘afford[ing] the best current scientific account of
relevant phenomena based on the available empirical evidence” (Gelman & Rhodes, 2012, p. 4).
I look at what is it about the how people think that makes learning the concepts about evolution
so difficult. While emotional responses based on religious beliefs block understanding and
acceptance (Kelemen, 2012), there is more to the situation. The logic progression that led
Charles Darwin to the conclusion that the mechanism of evolution is natural selection counters
aspects of the way people intuitively view the world. This paper outlines what intuitive
biological thought processes are, how they impede the understanding of evolution by natural
selection, and recommendations on how to promote evolutionary thinking based on addressing
these intuitive biological thought processes identified in the literature.
Intuitive Biological Thought and Evolutionary Science Understanding
Charles Darwin found a logical explanation for natural selection. I refer to these facts
and inferences in my discussion of intuitive biological thought processes, as well as additions
from the Evolutionary Synthesis, the combination of the findings from genetics to the principles
of natural selection (Futuyma, 2005). I find that there is a significant relationship of the intuitive
biological thought processes with Darwin’s logic progression and the additional details from the
modern understanding of evolutionary theory. Darwin’s logic progression follows the sequence
below, as outlined by Ernst Mayr (1982):
Fact 1: All species have such great potential that their population size would
increase exponentially . . . if all individuals that are born would again reproduce
Running head: UNDERSTANDING EVOLUTION
4
successfully.
Fact 2: Except for minor annual fluctuations and occasional major fluctuations,
populations normally display stability.
Fact 3: Natural resources are limited. In a stable environment they remain
relatively constant.
Inference 1: Since more individuals are produced than can be supported by the
available resources but population size remains stable, it means that there must be a fierce
struggle for existence among individuals of a population, resulting in the survival of only
a part, often a very small part, of the progeny of each generation.
These facts derived from population ecology lead to important conclusions when
combined with certain genetic facts [emphasis added].
Fact 4: No two individuals are exactly the same; rather, every population displays
enormous variability.
Fact 5: Much of this variation is heritable.
Inference 2: Survival in the struggle for existence is not random but depends in
part on the hereditary constitution of the surviving individuals. This unequal survival
constitutes a process of natural selection.
Inference 3: Over the generations this process of natural selection will lead to a
continuing gradual change of populations, that is, to evolution and to the production of
new species. (pp. 479-480)
The categories of the intuitive biological thought processes which follow are based on the
categorizations that the referenced authors use. The Evolutionary Synthesis concepts are
summarized from the Principles of Evolution that Futuyma (2005) lists that are additions to
Running head: UNDERSTANDING EVOLUTION
5
Darwin’s logic progression (see Appendix 1 for the full list).
There is a unifying intuitive biological thought process in all of the categories below: the
role of the individual. Natural selection occurs at the population level, with the changes in
proportions of genotypes in a population, not within the individual during its lifetime. This,
population thinking was one of the major concepts that Darwin introduced in his theory.
Psychological Essentialism
Psychological essentialism is the tendency to categorize the world into smaller
components. These components are believed to be “real” instead of human constructions (Coley
& Muratore, 2012; Gelman & Rhodes, 2012). The primary function of this categorizing
tendency is to break the immense amount of information present in the world up into manageable
chunks for efficient processing (Coley & Muratore, 2012). The components of the essentialist
intuitive biological thought process that impede evolutionary understanding are the homogeneity
and immutability of a particular species, individual organisms are in control of any changes,
those changes occur within the individual, and any changes are a progression toward an ideal
form (Coley & Muratore, 2012; Gelman & Rhodes, 2012).
Homogeneity of species. Fact 4 of the natural selection logic sequence emphasizes the
importance of variation in a population (Mayr, 1982). The Evolutionary Synthesis adds to this
concept. Alleles, equally stable alternative forms of a particular gene, arise from mutations, a
slow process from mistakes made during the DNA replication process. These alleles are the
genetic variation that occur in populations. Recombination that occurs in sexual reproduction
affects the proportions of the resulting genotypes that arise from the alleles (Futuyma, 2005).
The essentialist intuitive biological thought process does not recognize intraspecific (within
species) variation. This is a very common concept for students to misunderstand, and they
Running head: UNDERSTANDING EVOLUTION
6
usually only recognize interspecific (between species) variation as involved with evolution
(Bishop & Anderson, 1990; Coley & Muratore, 2012; Deaman & Kelly, 1978; Gelman &
Rhodes, 2012; Greene, 1990; Shtulman & Calabi, 2012). Essentialist thinking assumes that in a
category, e.g., species, each member share an “essence” that define the species (Coley &
Muratore, 2012; Gelman & Rhodes, 2012; Shtulman & Calabi, 2012). Coley and Muratore
(2012) define essence as the “underlying reality or true nature” of the category of organisms (p.
28).
Immutability of species. Inference 3 emphasizes that species change over the
generations (Mayr, 1982). The Synthesis adds to this. The same processes that cause
intraspecific genetic variation in the same population are responsible for differences between
populations of the same species, between species in the same genus, between genera in the same
family, on to all the higher taxonomic designations, i.e., natural selection over a long period of
time result in speciation (Futuyma, 2005). Essentialist thought processes counter this
evolutionary principle with stating that species do not change. The concept of “essence” is also
applicable here.
Inherent change. Inherent change concept contradicts the inferences in the logic
progression. Inference 1 emphasizes the struggle for survival only based on the access to
resources; Inference 2 emphasizes that unequal survival is based on a heritable component, and
Inference 3 is discussed in the previous paragraph (Mayr, 1982). The inherent change thought
process focuses on the individual as changing, progressing toward an ideal form (Coley &
Muratore, 2012; Gelman & Rhodes, 2012; Shtulman & Calabi, 2012). Ontological change, i.e.,
changes that occur during the development of an organism, and misunderstanding of
immunological processes of organisms can be mistaken for an example of evolution in an
Running head: UNDERSTANDING EVOLUTION
7
individual (Brumby, 1984).
Teleological Thought
Students are drawn to explanations that give a purpose to natural phenomena (Bishop &
Anderson, 1990; Brumby, 1984; Deadman & Kelly, 1978; Greene, 1990). Function becomes an
easy concept for students to associate with evolutionary change because that is how humans
approach design problems in general. Understanding that an external force is not directing
change is a difficult concept (Deadman & Kelly, 1978; Greene, 1990; Kelemen, 2012). Also,
since humans work on “improving” themselves, physique and health, it can be assumed easily
that other organisms do the same (Bishop & Anderson, 1990; Brumby, 1984; Deadman & Kelly,
1978; Greene, 1990; Kelemen, 2012). Kelemen (2012) identifies three types of intuitive
biological thought processes explaining evolution that are based on teleological thinking: basic
function-based, basic need-based, and elaborated need-based. The elaborated need-based
category is split into two sub-categories: effort-based and design-based (Kelemen, 2012).
Basic function-based and basic need-based. I combine these two thought processes
into one section because of the lack of the identification of a mechanism causing change by those
studied (Kelemen, 2012). In basic function-based thinking, the only reason that a trait comes
into existence is to perform a beneficial function (Kelemen, 2012). In basic need-based thinking,
the individual organism has an intrinsic power to change a heritable trait because of they “need”
it (Bishop & Anderson, 1990; Brumby, 1984; Deadman & Kelly, 1978; Kelemen, 2012).
Elaborated need-based: effort-based. The essentialist thought process of “inherent
change” is an influence on this teleological thought process. The genotype (the set of genes in an
individual’s DNA) determines what traits are passed on to future generation. Genes are discrete
entities that “retain their identity as they pass through the generations” (Futuyma, 2005, p. 10).
Running head: UNDERSTANDING EVOLUTION
8
The genotype determines the phenotype (observed characteristic) of an individual. However,
identical genotypes placed in different environments can have different phenotypes due to
external influences. The external influences do not affect the genotype, therefore acquired
characteristics are not inherited (Futuyma, 2005). This teleological thought process says that
changes that the organism acquires during its lifetime are passed on, often referred to in the
literature as “intuitive Lamarckism” (Brumby, 1984; Deadman & Kelly, 1978; Greene, 1990;
Kelemen, 2012).
Elaborated need-based: design-based. . This thought process emphasizes that an
external force is guiding change in the individual, often referred to by these designations: “God,”
“Nature,” or even “Evolution.” It is similar to the essentialist thought process of “inherent
change,” the progression toward an ideal state, however the agent of change is externally guided.
Interestingly, I found an example of this intuitive biological thought process in an article by van
Dijk and Reydon (2010) explaining aspects of evolutionary theory for teachers. On page 661,
the authors identify five points relevant to teachers concerning in the section entitled “The
Concept of Evolution and the Tree of Life.” In their third point they state: “Evolution as a
process often leads to more complexity because evolution can only work with the organismal
material that is already available, but it is not a process that necessarily leads to increasing
complexity” (p. 661). While they do try to mask it using the qualifiers “often” and “not . . .
necessarily,” this statement still reflects this type of intuitive biological thought process, the
progression toward an ideal, in this case, it is “complexity.” Inference 1, the struggle for survival
based on resource limitations (Mayr, 1982), implies that the organisms that are the most efficient
at acquiring resources and using energy are most likely to survive, not the increasingly complex.
Recommendations
Running head: UNDERSTANDING EVOLUTION
9
The research highlights several ideas of improving the teaching of evolution: teacher
awareness of the existence of intuitive thought processes and how they work, teaching formats
and curricula, and the timing of the introduction of concepts of evolution. Some online
resources, articles, and books are listed in Appendix 2.
Teacher Awareness. One of the most common points made in the literature is that
teachers need to be aware of what intuitive biological thought processes exist and their
underlying causes (Bishop & Anderson, 1990; Brumby, 1984; Deadman & Kelly, 1978; Greene,
1990; Shtulman & Calabi, 2012; van Dijk & Reydon, 2010). There are many resources online
(via the link in Appendix 2) that summarize the intuitive biological thought processes to watch
for in students.
Teaching formats and curricula. Brumby (1984) identified that in order for conceptual
change to occur, that there needs to be sufficient conflict between intuitive thought processes and
scientifically accepted evolutionary theory. The lecture format, a passive form of instruction, is
insufficient for this to occur (Brumby, 1984). Some researchers suggest introducing
evolutionary problems and have the students work out the results in order to see their faulty
reasoning processes themselves (Brumby, 1984; Greene, 1990).
Timing of the introduction of evolutionary concepts. Because of the importance of
evolution to biology and the life sciences, there are suggestions that evolutionary concepts
should be introduced at an early age (Evans, Rosengren, Lane, & Price, 2012; Kelemen, 2012).
Also, every biological subject should also tie into evolutionary theory (National Research
Council [NRC], 2012).
Vocabulary: Why is it important?
Vocabulary plays a huge role in the understanding of scientific concepts. The words used
Running head: UNDERSTANDING EVOLUTION
10
by the media and some scientists have conflicting meanings between the everyday usage and
scientific designations (Bishop & Anderson, 1990). In an attempt to make science more
accessible, this language reinforces intuitive biological thought processes. Students get confused
if the scientific terms are not precisely defined (Bishop & Anderson, 1990; NRC, 2012). Some
of those terms are: theory (NRC 2012), evolution (NRC,2012), adapt/adaptation (Bishop &
Anderson, 1990; Brumby, 1984; NRC, 2012), fitness (Bishop & Anderson, 1990), and selection
(NRC, 2012).
Conclusion
Brumby (1984) studied first-year medical students in Australia, the equivalent to college
freshmen in the United States. These students were considered the best biology students coming
out of secondary education in Australia. However, they still exhibited many intuitive biological
thought processes, even after the lectures on evolution and natural selection in medical school.
This was one of her closing observations: “Indeed it is more surprising to consider, not how little
these students knew, but how much they knew incorrectly, for their answers were given with
assurance, not hesitatingly” (p. 500)
References
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.
Brumby, M. N. (1984). Misconceptions about the concept of natural selection by medical
biology students. Science Education, 68(4), 493-503.
Coley, J. D., & Muratore, T. M. (2012). Trees, fish, and other fictions: Folk biological thought
and its implications for understanding evolutionary biology. In K.S. Rosgren, S.K. Brem,
E.M. Evans, & G.M. Sinatra (Eds.), Evolution challenges: Integrating research and
Running head: UNDERSTANDING EVOLUTION
11
practice in teaching and learning about evolution (pp. 22-46). New York: Oxford
University Press.
Deadman, J. A., & Kelly, P. J. (1978). What do secondary school boys understand about
evolution and heredity before they are taught the topics? Journal of Biological Education,
12(1), 7-15.
Dobzhansky, T. (1973). Nothing in biology makes sense except in the light of evolution. The
American Biology Teacher, 35(3), 125-129.
Evans, E. M., Rosengren, K. S., Lane, J. D., & Price, K. L. S. (2012). Encountering
counterintuitive ideas: Constructing a developmental learning progression for evolution
understanding. In K.S. Rosgren, S.K. Brem, E.M. Evans, & G.M. Sinatra (Eds.),
Evolution challenges: Integrating research and practice in teaching and learning about
evolution (pp. 174-199). New York: Oxford University Press.
Futuyma, D. J. (2005). Evolution. Sunderland, MA: Sinauer Associates.
Gelman, S. A., & Rhodes, M. (2012). “Two-thousand years of stasis”: How psychological
essentialism impedes evolutionary understanding. In K.S. Rosgren, S.K. Brem, E.M.
Evans, & G.M. Sinatra (Eds.), Evolution challenges: Integrating research and practice in
teaching and learning about evolution (pp. 3-21). New York: Oxford University Press.
Greene, E. D. (1990). The logic of university students’ misunderstanding of natural selection.
Journal of Research in Science Teaching, 27(9), 875-885.
Kelemen, D. (2012). Teleological minds: How natural intuitions about agency and purpose
influence learning about evolution. In K.S. Rosgren, S.K. Brem, E.M. Evans, & G.M.
Sinatra (Eds.), Evolution challenges: Integrating research and practice in teaching and
learning about evolution (pp. 47-65). New York: Oxford University Press.
Running head: UNDERSTANDING EVOLUTION
12
Mayr, E. (1982). The growth of biological thought: Diversity, evolution, and inheritance.
Cambridge, MA: Harvard University Press.
National Research Council and National Academy of Sciences. (2012). Thinking Evolutionarily:
Evolution Education Across the Life Sciences. Summary of a Convocation. Steve Olson,
Rapporteur. Planning Committee On Thinking Evolutionarily: Making Biology
Education Make Sense. Board on Life Sciences, Division on Earth and Life Sciences,
National Research Council, and National Academy of Sciences. Washington, DC: The
National Academies Press.
Scott, E. C. (2009). Accept it: Talk about evolution needs to evolve [Comment]. Science News,
176(3), 32. Retrieved from http://www.sciencenews.org/view/generic/id/45594/title/
Comment__Accept_it_Talk_about_evolution_needs_to_evolve_
Shtulman, A., & Calabi, P. (2012). Cognitive constraints on the understanding and acceptance of
evolution. In K.S. Rosgren, S.K. Brem, E.M. Evans, & G.M. Sinatra (Eds.), Evolution
challenges: Integrating research and practice in teaching and learning about evolution
(pp. 47-65). New York: Oxford University Press.
van Dijk, E. M. & Reydon, T. A. C. (2010). A conceptual analysis of evolutionary theory for
teacher education. Science & Education 19, 655-677. doi:10.1007/s11191-009-9190xAppendix
Evolutionary Synthesis addendum (Futuyma 2005, pp. 10-11)
1. The phenotype (observed characteristic) is different from the genotype (the set of genes in an
individual’s DNA); phenotypic differences among individual organisms may be due partly to
genetic differences and partly to direct effects of the environment.
2. Environmental effects on an individual’s phenotype do not affect the genes passed on to its
offspring. In other words, acquired characteristics are not inherited.
3. Hereditary variations are based on particles---genes---that retain their identity as they pass
through the generations; they do not blend with other genes. This is true of both discretely
varying traits and continuously varying traits. Genetic variation in continuously varying
traits is based on several or many discrete, particulate genes, each of which affects the trait
Running head: UNDERSTANDING EVOLUTION
13
slightly (“polygenic inheritance”).
4. Genes mutate, usually at a fairly low rate, to equally stable alternative forms, know as alleles.
The phenotypic effect of such mutations can range from undetectable to very great. The
variation that arises by mutation is amplified by recombination among alleles at different
loci.
5. Evolutionary change is a populational process; it entails, in its most basic form, a change in
the relative abundances (proportions or frequencies) of individual organisms with different
genotypes (hence, often, with different phenotypes) within a population. One genotype may
gradually replace other genotypes over the course of generations. Replacement may occur
within only certain populations, or in all the populations that make up a species.
6. The rate of mutation is too low for mutation by itself to shift a population from one genotype
to another. Instead, the change in genotype proportions within a population can occur by
either of two principal processes: random fluctuations in proportion (genetic drift), or
nonrandom changes due to the superior survival and/or reproduction of some genotypes
compared with others (i.e., natural selection). Natural selection and random genetic drift can
operate simultaneously.
7. Even a slight intensity of natural selection can (under certain circumstances) bring about
substantial evolutionary change in a realistic amount of time. Natural selection can account
for both slight and great differences among species, as well as for the earliest stages of
evolution of new traits. Adaptations are traits that have been shaped by natural selection.
8. Natural selection can alter populations beyond the original range of variation by increasing
the frequency of alleles that, by recombination with other genes that affect the same trait,
give rise to new phenotypes.
9. Natural populations are genetically variable, and so can often evolve rapidly when
environmental conditions change.
10. Populations of a species in different geographic regions differ in characteristics that have a
genetic basis.
11. The difference between different species, and between different populations of the same
species, are often based on differences at several loci or many genes, many of which have a
small phenotypic effect. This pattern supports the hypothesis that the differences between
species evolve by rather small steps.
12. Difference among geographic populations of a species are often adaptive, and thus are a
consequence of natural selection.
13. Phenotypically different genotypes are often found in a single interbreeding population.
Species are not defined simply by phenotypic differences. Rather, different species represent
different “gene pools”; that is, species are groups of interbreeding or potentially
interbreeding individuals that do not exchange genes with other such groups.
14. Speciation is the origin of two or more species from a single common ancestor. Speciation
usually occurs by the genetic differentiation of geographically segregated populations.
Because of geographic segregation, interbreeding does not prevent incipient genetic
differences from developing.
15. Among living organisms, there are many gradations in phenotypic characteristics among
species assigned to the same genus, to different genera, and to different families or other
higher taxa. Such observations provide evidence that higher taxa arise by the prolonged,
sequential accumulation of small differences, rather than by sudden mutational origin of
drastically new ‘types.”
Running head: UNDERSTANDING EVOLUTION
14
The fossil record includes many gaps among quite different kinds of organisms. Such gaps may
be explained by the incompleteness of the fossil record. But the fossil record also includes
examples of gradations from apparently ancestral organisms to quite different descendants.
These data support the hypothesis that the evolution of large differences proceeds incrementally.
Hence the principles that explain the evolution of populations and species may be extrapolated to
the evolution of higher taxa.Appendix 2
Online Resources For Improving Understanding of Evolution
http://nas-sites.org/thinkingevolutionarily/additional-resources/
This page is a collection of links put together by National Research Council and National
Academy of Sciences from the convocation in 2011 called Thinking Evolutionarily: Evolution
Education Across the Life Sciences. The summary of this convocation is found in the references.
Resources for Dealing With Pressure From Religious Communities
Dobzhansky, T. (1973). Nothing in biology makes sense except in the light of evolution. The
American Biology Teacher, 35(3), 125-129.
Most of Dobzhansky’s paper presents an argument against the literal interpretation of the
creation stories in the Abrahamic religions in a way that does not demean religion, he explicitly
says that he is a religious man, but demeans the arguments of the creationists of the time, which
have not changed much since, as “blasphemies, accusing God of absurd deceitfulness” (p. 126).
It is a great piece for teachers to read who are struggling with creationist pressures in their
personal lives, classrooms, and communities.
Scott, E. C. (2004). Evolution vs. creationism: An introduction. Westport CT: Greenwood Press.
This book presents the creationist and intelligent design arguments and how they are
incompatible with evolutionary science. It includes texts from the authors of non-scientific view
points.
Running head: UNDERSTANDING EVOLUTION
15
Roughgarden, J. (2006). Evolution and Christian faith: Reflections of an evolutionary biologist.
Washington DC: Island Press.
This particular book is good for demonstrating that science and faith are not mutually
exclusive.Footnotes
1
I worked briefly on a project with the Vanderbilt University Anthropology Department
on evolution education in Tennessee. The other investigators continually used the word “belief”
when referencing to what I define as “acceptance.” I use the term “acceptance” when referring
to scientific theories as suggested by Eugenie C. Scott, Executive Director of the National Center
for Science Education (Scott, 2009).