The letter of Aug. 30 by J. T. Bridges contains many misunderstandings about science in general and the theories of evolution and gravitation.

My purpose here is to counter Bridges’ mistaken claim that the theories of evolution and gravitation can not be compared because the former can not be tested directly.

Bridges’ views mirror those that I’ve encountered many times before, as they have been repeatedly touted by the many creationists — students, alumni and faculty members — who have graced this campus over the years. Such claims come in many forms but generally boil down to something like this:

“No conjecture or hypothesis can be elevated to the status of a credible scientific theory if it is based only on observations and inference. It must also be verified in repeatable tests carried out under controlled conditions, preferably in a laboratory setting.”

Were this true, Newton’s theory of universal gravitation would never have qualified as a credible scientific theory.

The motions of planets, comets and such were readily observable in Newton’s time, but no one could perform controlled experiments on extraterrestrial objects back then. They could only observe planetary motions from afar and formulate various inferences. They couldn’t manipulate or control the planets to carry out tests.

Newton didn’t even conduct experiments to demonstrate his inference that the force of gravity between two bodies varies as the product of their respective masses and inversely as square of the distance between them. Yet he boldly theorized that this formula applied not only to all visible objects on earth and in our solar system, but to all masses in the universe, observed or not.

Moreover, Newton had no hypothesis whatever for explaining how the effects of gravity could be communicated over such astronomical distances, as we know from his famous declaration, “I feign no hypotheses.”

This is most important, because with no idea as to the nature of the mechanism, there is no way to design experiments to test of verify it.

So, Newton’s theory of universal gravitation was based solely on observational data and reason. Its mechanism could not be verified with repeatable experiments because Newton posited no mechanism.

Darwin’s theory, like Newton’s, was rooted in observation and reason or inference, but in one respect, Darwin’s theory is vastly superior to Newton’s.

Unlike Newton, Darwin posited a plausible mechanism to explain how evolution could occur without any need for supernatural intervention or God-based miracles of any kind.

Darwin realized how effectively husbandmen had altered breeding populations of domesticated plants and animals just since the dawn of civilization. So, he simply proposed that with sufficient time, persistent selection, whether by the mindless influences of nature or by the conscious efforts of husbandmen, could eventually spawn new species from old.

Countless artificial selection experiments carried out in laboratories and on farms have verified beyond all doubt that selective breeding is indeed a most powerful mechanism for producing evolutionary changes.

But natural selection in the wild would have operated continuously over geological eras, which are thousands of times longer than the age of civilization or agriculture. Thus, Darwin proposed that natural selection could explain, not only the distributions of closely related fossils found in various sedimentary deposits around the world, but also the geographical distributions of currently living plants and animals — particularly those that exhibit the curious similarities in appearance and behavior that bewildered naturalists in Darwin’s time.

Against all the explanatory power, testability and experimental verification of Darwin’s theory, not to mention the many new and fruitful lines of basic and applied research it spawned, there stands the abject poverty of the God-based creation models. Ultimately, their only explanation for any observation is, “It so pleased God; case closed.” As regards the matter of repeated testing, they insist it is blasphemous to even think about testing God. (So there!)

In conclusion, it is no surprise that the scientific community is adamant on the following points:

1. That the occurrence of evolution has long ago been elevated to the status of established fact.

2. That natural selection, certainly the best explanatory mechanism for how evolution occurs, fully deserves its current status as a highly credible scientific theory.

3. That all the God-based models — e.g., creationism, intelligent design, sudden appearance, irreducible complexity, and so on — are scientifically worthless (if not counterfeit) and therefore deserve be banned not only from science, but from science classes in high schools, colleges and universities as well.

The only valid reason for including God-based explanations in science classes is to provide prime examples of what science is not.

John Patterson

Ames