Distinguishing Among Hypothesis, Theory, and Law

The following is taken from an article by Charles Kugler in The American Biology Teacher, Vol. 64, Number 5, May 2002, page341.


"All textbooks [examined] agree that hypotheses are tentative testable explanations. However, they seem to represent them in two ways. Some represent them as narrow and tied to particular studies or experiments. Some talk of hypothesis as explanations or generalizations of a body of work and may make no distinction between hypothesis and theories other than degree of support."

A theory is also a description or explanation of patterns or processes observed in nature, but we generally do not apply the term to explanations of specific observations or tests. Rather, authors agree that theories attempt to catalog and explain results and observations from a variety of sources, or related sets of systems or data."

In the summary of the article Mr. Kugler indicates that college textbooks are not consistent in their treatment of the term theory. Some suggest that theories are broad in scope, others indicate that they are strongly supported. His analysis reveals "that on one hand some concepts we call theories are not well supported. On the other hand, many well-supported concepts are simply not called theories."

He concludes; "when a concept becomes generally accepted, we drop the label and treat it as fact, except for the 'theory of evolution' and occasionally a few others."

"The few texts that define laws seem to agree that laws [or principles] are well-confirmed theories that are not likely to change; they are facts of nature. thus, laws are a subset of theories, and well-confirmed theories are facts."

Most biologists would agree that Evolution is a fact, whereas "evolution by natural selection " is a theory.

Kugler points out that "evolution was the only one of 20 concepts where each of the 12 textbooks explicitly pointed out uncertainties. Authors commonly emphasized scientific debates in evolutionary biology, but rarely even mention disagreements over other concepts."

Consider the following list of biological theories; choose one and write a three paragraph essay explaining:

  • Enzyme function by induced fit
  • Plasma membrane sturcture (fluid mosaic model)
  • Chemiosmosis mechanism for the production of ATP
  • Cell cycle control mechanisms
  • Operon mechanism of gene regulation in prokaryotes
  • Mendelian inheritance mechanisms
  • Clonal selection mechanisms of the immune system
  • Self-nonself recognition mechanisms
  • Sodium-potassium pump mechanism of resting and action potentials in nerve cells
  • Sliding filament mechanism of muscle contration
  • Calcium mechanism for stimulating muscle contraction
  • Stomatal control mechanisms
  • Xylem transport mechanisms
  • Phloem transport mechanisms
  • Human causation of global warming
  • Human causation of ozone depletion
  • Evolution by natural selection

Included June 20, 2002