Scientific Knowledge Of The Past Is Possible

Scientific Knowledge of the Past Is Possible

Confronting Myths About Evolution & Scientific Methods

R O B E R T A. C O O P E R

“C

reationists and evolutionists agree on real science—that is, the nature of the present world and how it operates. What we disagree on are our speculations about the past... . When properly understood, both evolution and creation are outside the bounds of empirical science, and, therefore, are incapable of scientific proof.” (Morris, 1998).

With this single passage, John Morris demonstrated that he subscribes to at least two of the 15 myths about science identified by McComas (1998) in a recent volume on the nature of science in science education. The two myths reflected in Morris’ statement are: (1) that there is a universally applied scientific method and (2) that experiments are the principal, or only, route to scientific knowledge. If we accept creationist John Morris’ account of “real science,” parts of what we now recognize as evolutionary biology, geology, and physics must be excluded since scientists in these disciplines may study historical events that cannot be replicated in conROBERT A. COOPER is a Biology teacher at Pennsbury High School, Fairless Hills, PA; [email protected].

trolled experiments. Unfortunately, many nonscientists see no problem with Morris’ assessment of the scientist’s ability to deal with historical events and are inclined to accept his conclusion that evolution and other historical sciences are unscientific. These widespread myths prevent creationist claims, like that of John Morris, from being critically analyzed or challenged by the public. Ruse (1998) observed that even those who are disposed to accept the fact of evolution will admit that “…there is something a little odd about the theory of evolution, either in structure or in the methodology it invokes” (p. 20). He added that by “odd” they usually mean that studies in evolutionary biology typically do not conform to the model of experimental science found in physics and chemistry. According to the common myths described by McComas (1998), scientists work through a sequence of steps that usually includes defining a problem, gathering information, proposing a hypothesis, making relevant observations, testing the hypothesis by directly observing the phenomenon during a controlled experiment, forming conclusions, and reporting the results. This is the standard textbook version of the universal scientific method. In the public mind, to make the claim that knowledge generated by this method is “scientifically proven” lends it an air of certainty that knowledge KNOWLEDGE OF LIFE’S HISTORY 427

in other disciplines presumably lacks. Conversely, any claim to knowledge that is not verified through the universal scientific method is necessarily suspect. In fact, for some critics like John Morris, if the work does not conform to the universal scientific method as described above, it isn’t science. Thus, by Morris’ account, since you cannot directly observe amphibians evolving from fish, humans evolving from ape-like ancestors, or replicate these phenomena in a controlled experiment, you cannot establish the reliability of such claims. In contrast to the simplistic, and incorrect, view of science reflected in Morris’ quote, documents that outline national standards for quality science instruction call for students to develop a richer and more accurate understanding of the nature of science as an essential component of scientific literacy (American Association for the Advancement of Science, 1990, 1993; National Research Council, 1996). For example, the Benchmarks for Science Literacy (1993) distinguish scientific inquiry from the overly simplistic popular view as follows: “It is far more flexible than the rigid sequence of steps commonly depicted in textbooks as ‘the scientific method.’ It is much more than just ‘doing experiments,’ and it is not confined to laboratories” (p. 9). There are actually many methods that scientists use to construct reliable knowledge. According to the National Science Education Standards (1996), “Scientific inquiry refers to the diverse ways in which scientists study the natural world and propose explanations based on the evidence derived from their work” (p. 23). There are many common methodological elements and values that run like a thread throughout the various disciplines in science (Smith & Scharmann, 1999). However, “scientists differ greatly from one another in what phenomena they investigate and in how they go about their work; in the reliance they place on historical data or on experimental findings and on qualitative or quantitative methods …” (AAAS, 1990, pp. 3-4, emphasis added). Scientific inquiry, as it is portrayed in these standards documents, encompasses attitudes, values, aims, and patterns of argument, as well as a variety of methods that have evolved throughout the history of science. The controlled experiment is only one among many methods used in science. The fact that historical events are unique and cannot be replicated in the laboratory does not prevent scientists from constructing reliable knowledge about them. This article presents the argument that, contrary to creationist claims and public perception, a variety of methods is used in science and among those methods are some that enable scientists to understand the past. It is an effort to make a small step toward the vision of science called for in the standards documents by describing some of the methods of problem solving used in the historical sciences. The methods described 428 THE AMERICAN BIOLOGY TEACHER, VOLUME 64, NO. 6, AUGUST 2002

here were originally developed by James Hutton, Charles Lyell, and Charles Darwin (Eldredge, 2000; Gould, 1986; Kitcher, 1993; Mayr, 2000), and they do enable scientists to investigate the past.

The Textbook Scientific Method The probable source of the John Morris’ portrayal of science can be found in existing textbooks (Duschl, 1990; McComas, 1998; Toumey, 1996). Science textbooks typically discuss the scientific process in the first chapter, listing some version of the steps in the universal scientific method as if the process consisted of the application of a standard formula that leads to facts. By way of example, most textbooks present a controlled experiment in this first chapter suggesting that this is the model form to which all scientists aspire. For example, the 1950s text, Modern Biology (Moon, Mann & Otto, 1956), while acknowledging that a variety of methods exists, placed greatest emphasis on testing of hypotheses by performing controlled experiments as being most characteristic of science. Little has changed in recent additions to the genre. In a new text, Johnson and Raven (2001) presented scientific methods in a manner very similar to Moon, Mann and Otto. Johnson and Raven wrote, “Although there is no single ‘scientific method,’ all scientific investigations can be said to have common stages …” (p. 15). They went on to present a sequence of steps similar to the universal scientific method described above and referred the reader to a figure on the same page that also contains the list of steps suggesting that the process is formulaic. The section continues with a description of a field study followed up by a controlled experiment. The inclusion of a field study is an improvement over many older textbooks; however, the authors did not identify the field study as such, nor did they discuss the comparative strengths and weaknesses of field studies and experimental studies. The student who reads this text is left to conclude that the experimental study, which matches the list of steps and is described in greater detail, is the approach of choice, or worse, may be the only choice in “real” science. McComas (1998) traced the origin of the multistep list presented as the universal scientific method in textbooks to two articles written by Keeslar (1945a, b). Keeslar’s (1945a) reflects the then prevalent empiricist philosophy of science which held that observations are primary, and laws and theories emerge as inductive generalizations from these observations. Duschl (1990) described how the traditional textbook presentation of scientific method emerged from this empiricist philosophy. The image of science typically portrayed in these textbooks promotes a ‘scientistic ideology,’ a belief that scientific authority is unlimited and that scientific

knowledge is established with absolute certainty (Duschl, 1988). Furthermore, scientism implies that the certainty and reliability of knowledge in any field must be judged by the degree to which that discipline adopts scientific methodology (usually meaning methods modeled after those of experimental physics and chemistry). By the 1950s, a new group of philosophers and historians began to look at the way scientists actually went about their work and found that many scientists do not conform to the rules of method and patterns of reasoning set down in most science textbooks (Duschl, 1985, 1990). The national standards documents reflect these more recent developments in the history and philosophy of science. As described by the national standards documents, there is a variety of methods used by scientists. Among these methods are some that enable scientists to address questions about historical events. The goals described in the standards documents will not be achieved with existing instructional tools and approaches. Textbooks must be revised to more accurately reflect more current views of the nature of science and scientific methods. Included among the methods addressed in textbooks should be the methods first developed in the 18th and 19th centuries to study historical events.

Methods for Studying Evolutionary History Scientists who attempt to reconstruct the history of life, the Earth’s geologic features, or the cosmos rarely perform the controlled experiments that textbooks describe, and their theories do not conform to the structure of theories as described by the empiricists. Yet, the conclusions they reach are no less reliable and no less scientific than those arrived at by performing controlled experiments. They typically construct narrative descriptions of sequences of events that are consistent with available evidence. To be testable, the narrative must also suggest additional evidence that should, or should not be, found if the story is correct. The work of historical scientists is similar to that of experimental scientists in its reliance on logical explanation, empirical evidence, parsimony, and many other characteristics that are shared by the various sciences (Smith & Scharmann, 1999)1. However, because the historical sciences deal with phenomena that are unique and unrepeatable in all of their details, they rely less on the verification of hypotheses through controlled experiments. Recognition of the fact that historical events can be the object of scientific study began to emerge in the late 18th and early 19th centuries related to then emerging 1

questions in geology and biogeography. Geologist James Hutton (1726-1797) made observations of processes occurring in nature around him and used those observations to interpret the events of the past (Eldredge, 2000). Building on Hutton’s work, Charles Lyell (1797-1875) wrote the influential three-volume work Principles of Geology in which he stressed Hutton’s principle of the uniformity of geological processes over time and also the idea that the gradual accumulation of small changes can, over long periods of time, lead to large-scale change (Eldredge, 2000). Darwin read, and was greatly influenced by, Lyell’s Principles. In his autobiography, Darwin wrote, “After my return to England [from the voyage of the Beagle] it appeared to me that by following the example of Lyell in Geology, and by collecting all facts which bore in any way on the variation of animals and plants under domestication and nature, some light might perhaps be thrown on the whole subject” (Darwin, 1876/1958, p. 119). Thus the development of methods for studying historical events culminated in the work of Charles Darwin, whose Origin of Species is the most influential book in biology, as well as one of the most influential in history (Mayr, 2000). In the Origin Darwin applied patterns of reasoning similar to Lyell’s in order to establish the plausibility of natural selection as a cause of large-scale evolutionary change. Darwin was, above all, a methodologist who showed the generations of historical scientists who followed how to proceed in order to scientifically investigate historical processes like evolution (Ghiselin, 1969; Gould, 1986; Kitcher, 1993). According to Kitcher (1993), the originality of Darwin’s thesis in the Origin of Species is the development of explanatory strategies aimed at answering families of important biological questions by applying Darwinian histories, descriptions of the probable historical events that led to the emergence of some structure or function presently observed in an organism. Kitcher (1993) argued that Darwin provided a means for answering questions about biogeography, comparative anatomy, embryology, and adaptation. The Origin is an extended argument that illustrates how Darwinian histories employ the concepts of descent with modification and natural selection to provide a single coordinating explanation for then outstanding problems in each of these areas of biology. Darwinian histories necessarily involve incomplete information about past events. History can never be recovered in all of its detail, yet based on a broad range of observations of the current state of affairs, one can find evidence to either support or refute a hypothetical historical narrative. For example, in the Origin, Darwin asked, Why are the endemic species of Galapagos

For interesting discussions of the methods and problems of historical sciences in the context of the dinosaur extinction controversy see Alvarez (1997) and Powell (1998). KNOWLEDGE OF LIFE’S HISTORY 429

finches so similar to South American finches? In reference to the South American life forms he wrote, “Here almost every product of the land and of the water bears the unmistakable stamp of the American continent” (Darwin, 1859/1964, pp. 397-398). Darwin hypothesized that the Galapagos finches were descended from mainland South American forms. His explanation for the current state of affairs, that is, the similarity between different finch populations, involved a discussion of the distance of the islands from the nearby mainland, the possibility of past migrations from the mainland based on naturalists’ observations of migration between mainland and islands in recent history, and the subsequent modification of the migrants by natural selection under the different environmental conditions of the islands. In short, given an entirely reasonable historical hypothesis about migration of species between mainland and island, the similarities between Galapagos and South American finches can be accounted for by genealogy and phylogeny (both histories), while the differences can be accounted for by natural selection resulting in adaptations to different local environments. A historical narrative becomes the coordinating explanation for the disparate facts assembled by Darwin in the case of the finches. In contrast to the methods used in experimental sciences, historical narratives, like Darwin’s explanation for the similarities in the finches, cannot usually be tested by performing controlled experiments. Historical narratives must stand or fall on the basis of whether they can consistently explain the evidence gathered from many different sources. Darwin’s Origin of Species (1859/1964) is full of examples of similar arguments in which a historical hypothesis of genealogical and phylogenetic relationships is shown to be more consistent with the available evidence than the rival hypothesis of multiple, separate creations. Gould (1986) provided a similar view of Darwin’s achievement as a methodologist; however, he took a broader look at Darwin’s career. Gould (1986) viewed several of the books written by Darwin as “… a covert, perhaps unconscious extended treatise on methodology…” (p. 62). According to Gould, Darwin’s achievement is the development of a graded series of three methods for inferring history from results or artifacts that can be observed. The first of these three methods involves the direct application of the principle of uniformitarianism, and includes cases where a process can be observed and measured in the present. Measurements of the rate of the process in question can be extrapolated over longer periods of time to explain large-scale results that can be observed. In The Formation of Vegetable Mould Through the Action of Worms (1881), Darwin measured the rate of soil turnover caused by earthworms and extrapolated that 430 THE AMERICAN BIOLOGY TEACHER, VOLUME 64, NO. 6, AUGUST 2002

measure over time to explain the subsidence of Stonehenge. Another example of direct application of this uniformitarian principle involves the measurements, by Peter and Rosemary Grant, of the changes in the genetic structure of finch populations on Daphne Major, an island in the Galapagos Archipelago. The Grant’s work demonstrates the high degree of responsiveness of a genetic system to changes in environmental conditions. This small-scale, genetic change measured by the Grant’s can be extrapolated over longer periods of time to explain the evolution of 13 species of Galapagos finches all descended from one ancestral South American form. All one need imagine is that there were sustained selection pressures in different directions for populations that were isolated from each other on different islands. The second of Darwin’s methods for inferring history from results or artifacts involves looking for stages or kinds that can be arranged in a logical sequence. Gould (1986) described how Darwin explained the existence of coral atolls as the last in a series of stages of reef growth around the edges of islands. In The Structure and Distribution of Coral Reefs (1842), Darwin developed a historical hypothesis placing fringing reefs, barrier reefs, and coral atolls as successive stages in the growth of a reef around a mid-ocean island, which subsequently subsided into the ocean. Measurements taken in the 20th century of the thickness of these different stages support Darwin’s hypothesis. A second example of this method might include any of the good fossil sequences that are available; for example, the fossils that illustrate the changes that occurred in the evolution of mammals from mammal-like reptiles. The third and final method that Gould (1986) attributed to Darwin involves making inferences about history from single cases. Darwin recognized that adaptations which approach engineering perfection, like the bird’s wing or the human eye, do not provide the strongest support for evolution. Because we see them only in final form, we cannot tell whether they evolved or they were designed. Darwin looked toward imperfect adaptations to support his theory because the imperfections show the path through history that led to the adaptation. Perfect, or near perfect, adaptations obscure their history. By way of example, Gould offered Darwin’s The Various Contrivances by Which Orchids are Fertilized by Insects (1862). In this book, Darwin argued that the various adaptations for fertilization found among the orchids are simply flower parts that have been modified by natural selection. Gould often refers to this as the panda principle in honor of his favorite example, the panda’s “thumb.” Analysis of the “thumb” used by pandas to strip bamboo leaves from their stalks shows that the thumb is not actually a digit, but rather is a modified wrist bone, the radial sesamoid. Gould argued, as did

Darwin, that the panda’s “thumb,” and other similar examples of functional but imperfect structures were produced by the historical process of descent with modification and not separately created (Gould, 1980).

Consilience - Evidence From Many Sources If we focus singly on only a few oddities like the panda’s thumb, or on the available hypothetical fossil sequences, the case for evolution may seem very weak. In order to appreciate the overwhelming strength of the support for evolution, one must simultaneously consider all of the evidence from many different sources. Darwin lamented the fact that few scientists in his day understood this. In a letter to Hooker written in 1861, Darwin wrote: “Change of species cannot be directly proved… the doctrine must sink or swim according as it groups and explains phenomena. It is really curious how few judge it in this way, which is clearly the right way” (quoted in Gould, 1986, p. 65). Judging from the ongoing evolution-creation debates, it would seem that there are still very few people who understand Darwin’s argument. Public debates over evolutionary claims, such as the emergence of Homo sapiens from ancestral hominids, often reflect this failure to understand the pattern of reasoning necessary for establishing support for claims in historical sciences. When the combined weight of all of the evidence is taken into account, the evolution of life through descent with modification is considered to be one of the most reliable conclusions of modern science. This is not to say that scientists who rely on historical evidence can establish their conclusions with absolute certainty. Since they have incomplete information about the past, their conclusions must always remain tentative. However, absolutely certain conclusions do not emerge in the experimental sciences either. All scientific interpretations of evidence must be held tentatively. Both the historical sciences and the experimental sciences establish increasing levels of confidence in the conclusions they reach by seeking many independent lines of evidence that all point to the same conclusion. This is why, in the experimental sciences, independent replication of experiments is desirable. When many independently conducted experiments all point to the same conclusion, scientists have more confidence in the conclusion. Ruse (1998) likens this character of science to the use of circumstantial evidence in a court of law. William Whewell, a 19th century British philosopher and historian of science, was the first to clearly articulate the fundamental principle that independent lines of evidence all pointing to the same conclusion allow scientists to claim increasing confidence in that conclusion (Gould, 1986; Ruse, 1998). The term used

by Whewell to denote this principle is consilience. In aphorism XIV of his Novum Organon Renovatum, Whewell (1858/1968) wrote: “The Consilience of Inductions takes place when an Induction, obtained from one class of facts, coincides with an Induction, obtained from another different class. This Consilience is a test of the truth of the Theory in which it occurs” (pp. 138-139). Ruse (1998) argued that: “[Consilience] is a method used constantly in science, and a mark that the work has been well done. Convergence on a common principle convinces us that we have moved beyond coincidence. … Darwin endorsed Whewell’s ideas entirely, and the Origin offers a textbook example of a consilience” (pp. 2-3). In the Origin, Darwin amassed many independent lines of evidence from artificial breeding, biogeography, comparative anatomy, embryology, and paleontology, all of which point to the same conclusion: that descent with modification by natural selection surely has occurred. Add to Darwin’s evidence the additional fossil finds that have accumulated since 1859, the many field and laboratory studies of natural selection, and the homologies in molecular sequences and the conclusion that Darwin was correct is inescapable.

Conclusions & Implications Science is understood by the public in terms of symbols and myths that perpetuate a view of science as a method of establishing absolutely certain knowledge through experiment (McComas, 1998; Toumey, 1996). Capitalizing on this widespread public misconception, creationists typically argue that both evolution and creationism are unscientific because neither can be ‘proven’ by a controlled experiment. This widespread misunderstanding of science prevents many from appreciating the power of evolutionary theories to explain adaptations of living things as well as life’s unity and diversity. Furthermore, misunderstandings about the nature of historical sciences prevent many from understanding that in a system where genealogical and phylogenetic relationships exist between elements, history must be part of the causal explanation for the current state of the system. The solution to this problem is to change the way textbooks portray scientific methods and bring the texts into line with the recommendations of the national standards documents. Textbooks should more clearly and completely address the diversity of scientific methods in that first chapter. Descriptions of successful studies in historical disciplines should be included in addition to the standard experimental studies in order to demonstrate for students that reliable knowledge of life’s history can be obtained. For example, Margulis’ SET or the development of the impact theory to explain the mass extinction at the Cretaceous-Tertiary boundary could be used KNOWLEDGE OF LIFE’S HISTORY 431

as excellent examples that would illustrate historical methods, as well as foster student interest (Alvarez, 1997; Powell, 1998). But discussions of method and the nature of science should not end with the first chapter. Rather than presenting science in its final form, that is, as a series of firmly established conclusions (Duschl, 1988, 1990; Schwab, 1962) throughout the rest of the text, authors should include discussion of the evolution of scientific ideas. What ideas preceded the currently accepted ones? Why were they rejected? What role did empirical evidence play? What methods were used? What role did historical and social factors play? As a result of such an approach, students may come to understand not only what scientists currently know, but also how they have arrived at those conclusions (Duschl, 1988, 1990). This approach to science education presents a view of science as a rational process for investigating and understanding nature. Such a view would enable students to achieve the level of literacy described in the standards documents and also effectively counter the arguments of creationists that evolution is not science, but is just another belief system.

Gould, S.J. (1986, January-February). Evolution and the triumph of homology, or why history matters. American Scientist, 74(1), 60-69.

Acknowledgment

Kitcher, P. (1993). The Advancement of Science. New York: Oxford University Press.

I would like to thank an anonymous reviewer for comments on an earlier draft of this article and also for suggesting the chapter from McComas (1998). The comments and chapter were very helpful in shaping the final form of this article.

Mayr, E. (2000, July). Darwin’s influence on modern thought. Scientific American, 283(1), 78-83.

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