Download 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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