Nature of Science

The Introduction to Explore Evolution packs a tremendous number of fundamental errors into a remarkably brief chapter. These errors bear not only on the science of evolution, nor even biology in general, but on the nature of science itself. The introduction fundamentally skews a student's understanding of what science is and how it is practiced. The definitions of evolution it provides are badly flawed and misleading, and misrepresent the state of scientific views on evolutionary biology with the clear goal of propping up a bogus creationist model of biology.

This chapter begins by introducing several basic errors about the nature of science. The first of these errors is a flawed distinction between historical sciences and experimental science, as if the scientific method were applied differently in different fields. The apparent goal of that distinction is to cast doubt on scientific knowledge regarding historical phenomena like the age of the earth and the diversification of life. This error is profound, as it misinforms students about the fundamentals of how science is practiced in every field. A similar error occurs when the authors misdefine how scientists determine "the best explanation." Since explaining a phenomenon after the fact is easy, merely explaining more evidence is not enough. Scientists judge explanations by their ability to make testable predictions, predictions which would disconfirm the theory if they were found to be wrong. Unlike the authors of this book, philosophers of science regard this testability as central to science, and regard approaches based only on verification and post hoc explanation as non-scientific.

"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).

Full discussion:

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.

Although the particle physicist and the astronomer may attend to both general laws and historical particulars, we can separate their two enterprises by distinguishing means from ends. The astronomer's problem is a historical one because the goal is to infer the properties of a particular object; the astronomer uses laws only as a means. Particle physics, on the other hand, is a nomothetic discipline because the goal is to infer general laws; descriptions of particular objects are only relevant as a means.

The same division exists within evolutionary biology. When a systematist infers that human beings are more closely related to chimps than they are to gorillas, this phylogenetic proposition describes a family tree that connects three species. The proposition is logically of the same type as the proposition that says that Alice is more closely related to Berry than she is to Carl. … Reconstructing genealogical relationships is the goal of a historical science.
Sober (2000) Philosophy of Biology 2nd ed., Westview Press: Boulder, CO. pp. 14-15

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.
Sober (2000), p. 18

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 great events of origin were singularities. The origin of the universe is not recurring. Nor is the origin of life, or the origin of major new forms of life. These are past singularities over which creationists and evolutionists debate. Evolutionists posit a secondary natural cause for them, creationists argue for a supernatural primary cause.
Geisler, Norman L. and J. Kerby Anderson (1987) Origin science: A proposal for the creation-evolution controversy. Grand Rapids, MI: Baker Book House, 198 p.

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.

At the earliest moments of the Big Bang, the Universe consisted of a searingly hot soup of fundamental particles - quarks, leptons and the force carriers. As the Universe cooled to 1000 billion degrees, the quarks and gluons (carriers of the strong force) combined into composite particles like protons and neutrons. The LHC will collide lead nuclei so that they release their constituent quarks in a fleeting 'Little Bang'. This will take us back to the time before these particles formed, re-creating the conditions early in the evolution of the universe, when quarks and gluons were free to mix without combining. The debris detected will provide important information about this very early state of matter.
Science and Technology Facilities Council (2008) "The Big Questions" page on "The Large Hadron Collider" website. Accessed September 18, 2008.

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.

Evaluating the quality of a scientific explanation

Summary of problems:

Scientific explanations are judged by their ability to make accurate predictions of new data. Explore Evolution obscures this point by stating that "The best explanation will be the one that explains more of the evidence than any other" (p. 5). This claim sneakily twists the student's understanding of how we evaluate scientific explanations. Doing that is necessary to get the subsequent erroneous claims through the door. It also cracks the door for a discussion of the supernatural in science classes, since the suspension of natural law can explain absolutely anything (making it useless as a scientific prediction).

Full discussion:

To be scientifically useful, an explanation ought to do more than merely explain existing observations. A good hypothesis may begin as an inference drawn from known facts, but it also must make some predictions which lead us to new observations. If the observations are not what we predicted, we can reject that hypothesis, but we do not regard it as proven if the observation is as predicted. That predictive power is part of what allows us to evaluate the quality of a scientific explanation.

The evidence in Explore Evolution would not allow us to distinguish between multiple hypotheses about who washed the car in their chosen example, nor is it impossible that some mischievous gremlin planted all of that evidence merely to make it seem as if someone washed the car.

Indeed, that latter hypothesis could explain any set of evidence we might possibly gather. It does not, however, predict the details of any new observation at all. That doesn't mean it's wrong, but it does make it a worse explanation than a hypothesis which makes testable predictions. This would be true even if it explained existing observations which existing theories did not explain, of the existing theories had a track record of producing correct predictions.

Philosopher Elliott Sober uses gremlins to make a related point:

You and I are sitting in a cabin one night, and we hear rumbling in the attic. We consider what could have produced the noise. I suggest that the explanation is that there are gremlins in the attic and that they are bowling. You dismiss this explanation as implausible. … I hope you see that, … If there actually were gremlins bowling up there, we would expect to hear noise. But the mere fact that we hear the noise does not make it very probably that there are gremlins bowling.
Elliott Sober (2000) Philosophy of Biology, 2nd ed., Westview Press:Boulder, CO. p. 32

Sober's point is that the gremlin hypothesis may be likely, but it is not plausible in part because it is not likely that there are gremlins in the attic to begin with. Thus, an explanation which seems to explain more evidence can be a worse hypothesis if it fails to make novel predictions, or if it requires us to invoke unlikely phenomena, such as the existence of gremlins.

Explore Evolution offers few hypothesis about biology, preferring to attack existing explanations. But where it does offer alternatives, they tend to exhibit the same flaws as the two "gremlin" hypotheses offered above. For instance, EE suggests that there may be multiple trees of life arranged in an "orchard". The gremlin(s) which tend that orchard could undoubtedly have planted it in any way, and they could have been planted in a manner which produces a pattern of modern diversity indistinguishable from what we would find if there were a single tree of life (which is to say, indistinguishable from what we actually find). A hypothesis involving multiple trees of life requires us to understand multiple origins of life, and a hypothesis involving an orchard of trees (rather than a forest) requires that we hypothesize something capable of planting and tending all of those trees. The orchard hypothesis and the single tree hypothesis might both explain all the extant data, but to hypothesize an orchard raises more questions than it resolves, while making no novel, testable predictions in its own right. This makes it a worse explanation, and these flaws would persist even if it could account for observations that existing hypotheses cannot explain.

Again, the misrepresentation of basic issues in the nature of science invalidate the book, even if the misrepresentations were not clearly intended to open the door to nonscientific ideas in the science class.


Cleland, Carol E. "Historical science, experimental science, and the scientific method", Geology 11:987-90, 2001.

Cleland, Carol E., "Methodological and Epistemic Differences between Historical and Experimental Science," Philosophy of Science 69,474-96, 2002.

Miller, K.B. "The similarity of theory testing in the historical and 'hard' sciences." Perspectives on Science and Christian Faithe 54:119-122, 2002.

For more information

Peter Lipton (2005) "Testing Hypotheses: Prediction and Prejudice" Science 307(5707):219-221.

Lipton explains some reasons why we should prefer predictions to post hoc explanations.