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"Historical science" vs. "experimental science"
Summary of problems:
Explore Evolution relies on an ill-defined distinction between "experimental science" and "historical sciences," and asserts that claims about the latter cannot be directly verified. While the terms Explore Evolution uses are indeed applied by philosophers of science, those philosophers use the terms quite differently. Both approaches to scientific questions are valid, a given scientific field can draw on both approaches, and neither approach is less scientifically powerful. Explore Evolution is wrong to state that these different approaches require "different methods," and even more wrong to state that "in the historical sciences, neither side can directly verify its claims about past events" (p. 3).
Philosophers of science draw a distinction between research directed towards identifying laws and research which seeks to determine how particular historical events occurred. They do not claim, however, that the line between these sorts of science can be drawn neatly, and certainly do not agree that historical claims are any less empirically verifiable than other sorts of claims. Philosopher of science Elliott Sober explains:
This division between nomothetic ("nomos" is Greek for law) and historical sciences does not mean that each science is exclusively one or the other. The particle physicist might find that the collisions of interest often occur on the surface of the sun; if so, a detailed study of that particular object might help to infer the general law. Symmetrically, the astronomer interested in obtaining an accurate description of the star might use various laws to help make the inference.
Sober continues by observing that the sort of mathematical modeling undertaken by some evolutionary biologists is not historical in this sense, but seeks after the sort of general "if-then" statements which include scientific laws. Evolutionary biology thus is both a nomothetic science and an historical science. Furthermore:
Although inferring laws and reconstructing history are distinct scientific goals, they often are fruitfully pursued together. Theoreticians hope their models are not vacuous; they want them to apply to the real world of living organisms. Likewise, naturalists who describe the present and past of particular species often do so with an eye to providing data that have a wider theoretical significance. Nomothetic and historical disciplines in evolutionary biology have much to learn from each other.
As an example, Sober points to ongoing research into the origins of sexual reproduction. Biologists pursuing historical scientific programs have identified a number of species which do and do not reproduce sexually, and have reconstructed the evolutionary relationships between these species. Other researchers have developed generalized models which show that sexual reproduction ought to evolve under certain circumstances, and that asexual reproduction is more advantageous under other conditions. If both groups worked independently, they might consider the problem solved. By working together, the theoreticians can see which model of the origins of sex is most applicable to any given lineage, testing the model and yielding both historical and theoretical insights. Through such collaborations, researchers have found that the precise conditions and predictions of existing models for the evolution of sex do not match the actual circumstances observed, indicating that theoretical work remains to be done, and that further research in the field is necessary.
Sober concludes "[o]nly by combining laws and history can one say why sex did evolve" (p. 18, emphasis original). This contrasts sharply with the claim in Explore Evolution that "in the historical sciences, neither side can directly verify its claims about past events" (p. 3). Explore Evolution here seeks to sow doubt about certain scientific results, and as a consequence, presents an inaccurate description of the scientific process. Both acts are irresponsible for a textbook, but the latter will have consequences on the students' successes in all their scientific endeavors.
See also Carol E. Cleland (2001) "Historical science, experimental science, and the scientific method" Geology, 29(11):987-990 for a discussion of why "the claim that historical science is methodologically inferior to experimental science cannot be sustained."
Explore Evolution follows a long history of creationist misrepresentation on this point. Creationists have long attempted to undercut the validity of evolutionary theory by claiming that it is not genuine science and therefore need not be taken seriously. Evolution has been called "just a theory" as opposed to fact, "speculative" as opposed to demonstrated, and "historical" as opposed to "experimental."
For example, in the creationist book The Mysteries of Life's Origin (1984), Charles Thaxton, et al. contrast supposedly reliable operations (experimental) science with the "speculative" science of origins. Similarly, in Origin Science: A proposal for the creation-evolution controversy, Norman Geisler and Kerby Anderson attempt to resolve that social controversy by distinguishing "empirical" or "operational" science (equivalent to Explore Evolution's "experimental science") from "forensic" or "origins" science (equivalent to "historical science" in Explore Evolution:
It is the proposal of this book that a science which deals with origin events does not fall within the category of empirical science, which deals with observed regularities in the present. Rather, it is more like a forensic science, which concentrates on the unobserved singularities in the past. … A science about the past does not observe the past singularity but must depend on the principle of uniformity (analogy), as historical geology and archaeology do. That is, since these kinds of sciences deal with unobserved past events (whether regular or singular), those events can be "known" only in terms of like events in the present. …
The problem with these attempts to divide science neatly into two piles is that, as Sober observes, a given science, and even a given scientist, can switch between approaches in the quest to address a single question. Geologists can plumb the oldest rocks on earth for evidence of the first life, but they can also go to the lab and recreate the conditions of early earth to test predictions of hypothesis about events billions of years ago. And those results from a modern laboratory will send researchers back to the field to test predictions about historical events generated in the laboratory.
Similarly, physicists at the Large Hadron Collider in Switzerland are testing theories about the origin of the universe:
The LHC will recreate, on a microscale, conditions that existed during the first billionth of a second of the Big Bang.
Which category of science does this belong to? Clearly, it is both historical science and experimental science. Other such historical claims can be evaluated using modern experiments. Another example of this approach can be found in the episode of Mythbusters in which claims about the destruction of the Hindenburg are tested using modern models of the combustible zeppelin. If a television show can accurately navigate these philosophical waters, it is entirely appropriate to expect a textbook to handle them responsibly as well.