Evolution & the Nature of Science
Martin K. Nickels
This article presents the philosophy and general content of the authors' ENSI program. It makes the case for the importance and potential effectiveness of presenting, in any proper biology course, first the elements of the nature of science (what it is and is not, its uncertainty, yet its usefulness), followed by an introduction to evolution, preferably using the study of human evolution as the most powerful vehicle for teaching both the nature of science and the nature of evolution. All of this is best done with a series of open-ended, hands-on critical-thinking lessons. The article is about 6 pages long.
Evolution & the Nature of Science
TEACHING about evolution in high school biology poses a pedagogical predicament for teachers: While on the one hand there is no idea more central to modern biology, nor any better supported, on the other hand there is in the popular (and student!) mind no topic more controversial in all of science. Despite the importance of evolution in modern science, but fearing confrontation, many teachers slight or even completely ignore the topic altogether. Not only is this an omission of a major section of biology, it is a further disservice to students because it allows them to continue to embrace major misconceptions without challenge. Thus, evolution remains a minority view in the general understanding, a theory rejected by far too many college students, adults, and, even high school biology teachers (e.g. Eve & Dunn 1989; Nickels & Drummond 1985; Rensberger 1994; Zimmerman 1987).
This conflict between scientific importance and public resistance makes the effective teaching of evolution perhaps the single most important task for reforming the teaching of high school biology, which is currently the last science course taken by the majority of American voters. Here we describe an innovative model for improving the teaching of evolution in high school biology courses. The model has been demonstrated to be highly effective-due in no small part to having been classroom-tested and refined by more than 500 teachers in 18 states over the past six years. The model combines the teaching of evolution with both a modern view of the nature of science (which enables teachers to deal with potential controversy in a very effective manner) and the use of humans as the primary case study for understanding evolutionary concepts. Pedagogically, the model requires consistent use of student-centered activities that allow students to experience what it is like to do science rather than only read, or be lectured, about it.
We introduced this model in 1989 through the first of a series of "Evolution and the Nature of Science Institutes (ENSIs)" for high school biology teachers. These institutes were funded through 1995 by a series of three grants from the National Science Foundation.
Much of the ENSI program anticipated and subsequently paralleled national and state efforts to improve the teaching of science. An integration of evolution with an emphasis on the nature of science has since been supported repeatedly in various reports from the American Association for the Advancement of Science (e.g. Project 2061). Most recently the National Research Council has issued its National Science Education Standards which start with the Nature of Science and include evolution as one of only eight other fundamental ideas across all of science. States such as California (1990) and Michigan (1991) have adopted guidelines for science teaching that emphasize the importance of teaching about the nature of science and integrating it with specific scientific knowledge at virtually every grade level. These states also include evolution as a theme throughout their newly-modernized K-12 guidelines. Similarly, these major reviews and state guidelines emphasize the importance of shifting from authoritative teacher lectures to student-centered investigative learning.
Refocusing High School Biology
Four themes underlie the approach we advocate: First, and crucially, science is both inescapably rooted in inherent uncertainty and yet capable of producing highly reliable knowledge. Second, evolution can best be understood when seen as an example of modern scientific thinking. Third, human evolution is one of the best case studies of modern evolutionary knowledge. Fourth, non-dogmatic pedagogies are essential in teaching science, both because they increase learning and because they help students to acquire the critical thinking skills central to science and to its comprehension.
Theme 1: Modern Science & Uncertainty
Clearly, teachers need to present current scientific knowledge. But, some (if not most!) of the factual scientific knowledge that students learn in high school will be replaced by newer knowledge during their lifetimes. Cultivating an understanding and appreciation of science as a process that produces ideas that are likely to eventually be made obsolete as they are replaced with enhanced and improved knowledge should be essential to science education. Students need to learn to value a process that generates enhanced scientific understanding despite the fact that such enhancement supersedes or may even contradict what they learned earlier.
Central to the approach advocated here is a considerably more realistic model of the nature of science than is found in any high school textbook or even introductory college textbooks. Three aspects of modern science are critically important in this model.
First, it is essential to distinguish between science and non-science. Science deals only with the natural realm; explains only with empirically accessible (natural) forces; and assumes the uniformity of natural processes throughout time and space unless empirical evidence indicates otherwise. With this distinction, it is clear that because of their "un-natural" nature some issues (e.g. the existence and fate of a spiritual essence or soul) and some questions ("How much does a soul weigh?") are outside the realm of scientific inquiry.
Second, scientific knowledge is fundamentally and irrevocably uncertain. The fluid nature of scientific knowledge is demonstrated not only in the failure of the classical certainties (e.g. Newtonian physics) to be certain, but also in the day-to-day refinements and revision of "facts" and scientific theories. There are several reasons for this uncertainty, including the fact that scientific knowledge is contingent knowledge (dependent on the presently available evidence only).
Complexity and theory-ladenness are fundamental sources of scientific uncertainty. The complexity of reality usually precludes the certain delineation of all possible alternatives to any hypothesis. Recall J. B. S. Haldane's suspicion (1927:286): "The universe is not only queerer than we suppose, but queerer than we can suppose [his emphasis]." We can never be sure that we have formulated-let alone, assessed-all possible alternative explanations. This, alone, often precludes either certain proof or certain falsification of scientific ideas (Kitcher 1982; Nelson 1989). (For example, since no one knew that radioactive decay in the center of the earth was continually generating planetary heat, Lord Kelvin argued in the 1800s that the earth was steadily cooling and therefore was too hot to be more than 100 million years old. Similarly, the idea of "continental drift" or plate tectonics was rejected initially for lack of evidence of any known geological process powerful enough to move continents.)
The impossibility of dependably envisioning all possible alternative explanations is underscored by the realization that scientists live and work at specific times in history and in evolving societies that determine and constrain much of their thinking. Stephen Jay Gould provides several such examples in various essays dealing with the history of biological thought (e.g. Gould 1985). Glen (1994) details a recent example dealing with the issue of the extinction of the dinosaurs.
Further, we endorse Jacob Bronowski's argument (1978) that since fundamental scientific progress depends on making new connections and the number of potential connections is unlimited, the prospect of scientific change and advancement is equally unlimited.
Third, despite these many sources of fundamental uncertainty, science not only manages to produce ideas that are reliable enough to have immense practical importance, it also manages to make considerable progress in developing major new insights. How can this be? Rather than insisting that their explanations be absolutely true, scientists use a variety of criteria to compare alternative explanations so as to distinguish the better or more adequate explanations from the less adequate ones. Primary among these criteria are, first, the extent to which each explanation conforms to the patterns of relevant data and, second, the extent to which each alternative can comprehensively account for diverse data. Another important criterion is the predictive power and accuracy of one theory compared to another. Additional criteria include the extent to which there are independent, congruent patterns of data and evidence consistent with an explanation; the extent to which anomalies or exceptions are explicable; and the extent to which an explanation relies upon only scientifically accessible processes.
Theme 2: Modern Evolutionary Theory
Evolution is central to modern biological thinking. Every branch of modern biology is rooted in the evolutionary perspective of the organic world. There is no contemporary scientific rival to evolutionary theory as the major explanatory paradigm across the discipline. Biological evolution is thus an especially good example of a powerful scientific theory because it is supported by, and explains, an almost unparalleled number of strong and independent bodies of evidence, predictions and confirmations.
Bodies of evidence that support evolution include the existence of natural, discrete, hierarchically nested groups of organisms; the congruent nature of molecular, anatomical and physiological similarities between organisms; both the adaptive and non-adaptive (or historically-constrained) nature of specific biological characteristics of organisms; and a paleontological record showing a combination of temporal succession of species, intermediate or transitional forms, and ecologically coherent fossil assemblages. Together, these data patterns are accepted as currently irrefutable scientific support for the inference that all modern species evolved from various common ancestors through a historically-contingent series of branching and extinction events characterizing the history of life on this planet.
The natural processes that biologists use to account for the bodies of evidence cited above include both random (with respect to the needs of the organism) and non-random ones. Many of the misconceptions about the nature of biological evolution stem from the failure to distinguish between these random and non-random processes. Among the random biological processes are genetic mutation, sexual recombination of parental genes, genetic "drift" of small gene pools, and genetic admixture resulting from interbreeding between different populations. Other random processes (again, with respect to the needs of the organism) that induce and/or influence biological evolution include geographical, climatic and geological changes in a population's environment. Still another sort of "randomness" that has influenced the course of biological evolution on this planet includes the fortuitous nature of specific natural historical events such as mass extinctions.
The principal non-random process that can produce evolutionary changes in populations and species is natural selection through differential fertility. The splitting of one species into two or more or the transformation through time of one species into another are the modes by which "the origin of species" or speciation occurs. When combined with the nearly 4 billion years that have elapsed since the origin of life on this planet, the interaction of all of these natural processes is regarded as sufficient by scientists to account for the appearance of the biological world as we see it today.
Theme 3: Humans as a Case Study in Evolution
The recognitions that humans are not "creatures" set apart from nature but are clearly animals and, therefore, both a part of nature and a product of natural (biological) processes are among the most profound ideas of the last two centuries. Concentrating on humans when teaching evolution builds on the common practice in high school biology of using humans to demonstrate patterns in anatomy, physiology and genetics. But what has seldom been done is to connect these patterns with evolutionary theory. Using humans as a case study of evolution is pedagogically effective because it takes advantage of students' innate interest in themselves and because it deals directly with one of the most common public misperceptions associated with evolution.
Few high school biology teachers are familiar with the large body of knowledge dealing with human evolution (Nickels 1987). Yet, there are few other species that have been studied as extensively. Charles Darwin's 1871 The Descent of Man effectively initiated the scientific study of human evolution. Darwin concluded from T. H. Huxley's anatomical evidence that of all living primates, the African apes (chimpanzees and gorillas) are most closely related evolutionarily to humans and, therefore, we should most likely look in Africa for the fossil evidence of our shared common ancestor with them, although there was not a single primate fossil known from Africa at the time.
Since 1871, anatomical research on virtually every one of the approximately 200 species of primates has been conducted. In addition, in the past three decades, biochemical comparisons have been extensively developed and support the earlier conclusions from morphology. With respect to fossil evidence, since 1871 there has been a virtual avalanche of discoveries from every continent except Antarctica. We now have literally hundreds of hominin (formerly "hominid") fossils dating from as old as 4.5 million years ago when the first erect, bipedal forms appeared in Africa. The major anatomical, skeletal and dental evolutionary changes through time are well-documented and supported by multiple fossil specimens. Added to these extensive bodies of knowl-edge about the course of human evolution is the unique situation regarding human behavioral evolution. Much more is known about the behavioral evolution of humans than of any other species because of our predecessors' development of material culture and our discovery of the remains of that unique legacy.
Theme 4: Developing Critical Thinking in Biology Classes
Biology teachers must convey to students that science is a process of determining what to accept in the absence of certainty. For this reason, critical thinking skills should be the most fundamental part of any science course. There are teaching techniques that emulate the critical thinking skills (the "scientific methods") which scientists use in evaluating the relative merits of alternative explanations. Application of these techniques allows students to learn how science is done while gaining knowledge about biology. Two key issues must be dealt with in order to permit and encourage students to develop critical thinking skills: coverage and participation.
The tradition that a teacher must cover everything has created a dilemma especially acute in the sciences. As scientific knowledge increases at an unprecedented pace, so does the frustration level for teachers who have only so much time for teaching. Not only is it unrealistic to attempt to cover all of biology, it is clearly futile and self-defeating. When attempts to touch on too many of the important ideas limit presentations to only conclusions and explanations without supporting evidence, they are counterproductive. When students are asked to learn science by merely memorizing conclusions, science appears little different from dogma. A teacher must acknowledge that it is impossible to cover everything and that it is actually more effective to cover fewer concepts in much greater detail. (This "less is more" approach has also been advocated in the national and state frameworks discussed earlier.)
The question then becomes which major concepts to treat in greater detail. We urge teachers to present fewer major concepts but to treat these in greater detail. Foremost among the essential concepts are the nature of science and evolution. Furthermore, we recommend that teachers introduce these concepts early and use them as themes throughout the course. Beginning biology with the nature of science provides students with the mindset and cognitive tools that are needed in the remainder of the course. A solid understanding of evolution enables students to better understand other biological concepts.
Once breadth of coverage is replaced with depth of coverage, attention must turn to pedagogy. Developing an understanding of science based on critical thinking requires active participation by students. Unfortunately, high school science courses too often employ "laboratory activities" that only lead to a predetermined right answer. Far too few students are allowed to participate in a real experiment, let alone plan or execute one.
Only by engaging in the scientific process, can students truly learn how it works. Students must be permitted to experience phenomena and develop their own sense of what happens and what does not in order to understand the ideas being taught. Developing a testable hypothesis, gathering data, and planning a retrial take practice. Open-ended activities where there is no teacher-imposed right answer at the end convey the inherent uncertainty in science and the necessity of working with only tentative conclusions. Labs that allow for real data gathering, rather than merely confirming the text or teacher's information, reinforce the difficulties of obtaining reliable data. Collaborative group activities model the working style of many scientists. Teachers can even conduct "experiments" comparing the effectiveness of course changes to illustrate scientific research for students. Continuous assessment by peers and teachers using techniques that encourage reevaluation, revision and resubmission of student work is appropriate because scientists themselves engage in a continual process of updating and revising their explanations.
We suggest that the initial unit on the nature of science include a number of student activities which are open-ended and could lead to student hypothesis generation and testing, and to the development of models and explanations. In these activities no confirmation of correctness should come from the materials or from the teacher. Such activities set the stage for biology students to question dogmatic teaching and the text as "truth" and should be continued through-out the course.
The Pedagogical Predicament Resolved
Because evolution is a prime example of outstanding science and because it is required for any adequate understanding of modern biology, evolution is a powerful topic for teaching both about the nature of modern science and about the state of biology. Rather than shying away from teaching about evolution (especially human evolution) because of potential controversy and the difficulties that might ensue, teachers should use evolution as an ideal opportunity for illustrating the nature of modern science (Nelson 1986). Moreover, by emphasizing the tentative nature of all science, the direct conflict between evolution and religious dogma is reduced and students can better consider both evolution and science in general (Nelson 1986, 1989). By making a clear separation of science from other ways of knowing and by teaching students to think, analyze and compare available information, evolution need not be a controversial subject in science education. Using humans to illustrate modern evolutionary thinking capitalizes on students' inherent interest in themselves and emphasizes that humans are both a part-and one of many products-of the natural world (Nickels 1987).
As our experience with ENSI shows, teachers can successfully use evolution and the nature of science as organizing themes for their entire biology course. Using these two themes in conjunction throughout the course enables them to continually illustrate the process of scientific thinking by reference to a specific example of scientific theorizing. Using evolution as possibly the best example of the nature of the scientific process we have today, teachers can successfully increase student understanding of the nature of modern science, modern evolutionary theory, and the scientific evidence that humans and all other species have evolved. Such success serves both students and society well.
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