Friday, May 24, 2013

Scientific Fact, Theory, and Law: A creationist tutorial

There is a common error made by creationists discussing evolution regarding the ideas of "fact," "scientific theory," "hypothesis," and "scientific law." It is common enough to warrant a separate comment.

Quoting from the National Academy of Science (USA):

In science, a "fact" typically refers to an observation, measurement, or other form of evidence that can be expected to occur the same way under similar circumstances. However, scientists also use the term "fact" to refer to a scientific explanation that has been tested and confirmed so many times that there is no longer a compelling reason to keep testing it or looking for additional examples. In that respect, the past and continuing occurrence of evolution is a scientific fact. Because the evidence supporting it is so strong, scientists no longer question whether biological evolution has occurred and is continuing to occur. Instead, they investigate the mechanisms of evolution, how rapidly evolution can take place, and related questions. 2008 "Science, Evolution, and Creationism"

Now lets consider the idea of a hypothesis. In science, it is a statement that there exists an unobserved phenomena, or event which is a critical prediction of a scientific theory. This was proposed as a way to test the validity of a scientific theory called "the experimental method." We trace this back to Francis Bacon in the 1600s. By the 20th century, the notion that a "good" theory must generate experimental tests became a central topic of philosophers like Carl Hempel, and Karl Popper. Even before actually testing a hypothesis Hempel and Popper in a rare point of agreement between them, thought that a "good" theory had to generate hypotheses.

When asked if evolutionary theory was testable, J.B.S. Haldane famously replied, "Show me a fossil rabbit in the Precambrian." This was reportedly in reply to a question about the falsifiability of evolutionary theory.

Next there is the gross misunderstanding of what a "scientific law" is, and how it is related to a scientific theory. A scientific "law" is a generalization of empirical observations that is typically reduced to a mathematical formula. These "laws" are always bound within the observational frame, or external conditions of the observations. They are not explanations of the observed phenomena. My favorite example is Ohm's Law, I = V/R. It will always work under the conditions that Ohm used to observe electrical current, voltage, and resistance. However, you cannot find in Ohm's Law a theory of the electromagnetic field. You cannot even derive one. Further, Ohm's Law is invalidated at extreme temperatures- the classic example is resistance free superconductors- variable voltages, and extreme voltages. This does not mean that Ohm's Law is not useful, but it is only useful for the external conditions that allow it be applied.

A scientific theory does not "graduate" to being a "law" or a "fact." There is a second common error made by creationists which is repeated in nearly every discussion with creationists, and that is that evolution has not been expressed in the mathematical precision of a "law." It will surprise some people, but this was published in 1908, over a century ago. The exact example is the generalized Hardy-Weinberg Equilibrium equation. For computational reasons, they presented it as, "IF evolution did NOT occur, then ...Equilibrium" which can confuse some students.

Hardy, G. (Jul 1908). "MENDELIAN PROPORTIONS IN A MIXED POPULATION.". Science 28 (706): 49–50. doi:10.1126/science.28.706.49. ISSN 0036-8075. PMID 17779291

Weinberg, W. (1908). "Über den Nachweis der Vererbung beim Menschen". Jahreshefte des Vereins für vaterländische Naturkunde in Württemberg 64: 368–382.


Christian said...

This is a valuable post. I just wish explaining things to creationists was this easy. I wish they could understand that we say evolution is a fact because all the evidence (DNA and fossils) shows it.

Gary S. Hurd said...

I am glad you liked it.

Hobbes said...

Very good! I found you from your post on Disqus. It always astonishes me how strong is the Power of Myth. No matter the logic of reason, it is roundly rejected by the true believer. There has to be deep insecurity at their very core.

Hobbes said...

I meant to mention, my blog is at

Gary S. Hurd said...

Welcome Max. I hope you find some of this useful.

Hobbes said...

Thanks Gary. I'm sure I will.