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Origins of species, etc.

Is evolution merely a "theory"?

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bullet"The great tragedy of science - the slaying of a beautiful hypothesis by an ugly fact." T.H. Huxley

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Many creation scientists have stated for decades that since evolution is only a theory, that it is not an established principle in science. Back in the 1920's, William Jennings Bryan, an orator, politician, and conservative Christian, used to say "It is guesses strung together." Back in 2002, the Cobb County school board of suburban Atlanta, GA required that biology textbooks be provided with a sticker saying that "Evolution is a theory not a fact, regarding the origin of living things." 11

In reality, the theory of evolution is much more than "just a theory" as the term is normally used.

The word "theory" in normal usage means a guess or a hunch. But in science, a "theory" is a belief that has been generally accepted by scientists as a result of extensive experimentation and/or observation.

Most biologists believe that evolution is more than a theory; it is an established fact. The earth's life forms have, in fact, evolved over billions of years. Species of animals have been recently observed as continuing to evolve, both in the lab and field.

There remains debate about some details of past evolution. For example, there is a consensus that dinosaurs evolved and that birds evolved; there is still some debate as to whether dinosaurs were the distant ancestors of birds. There is also a debate about whether natural selection, as proposed by Darwin about 150 years ago, is the only process that drives evolution. But there is a nearly total consensus among biologists that evolution actually happened and continues to happen today.

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The theory of evolution is not just a "theory":

Words in English often have multiple meanings. Words about origins are no exception.

  • In popular usage:

    • "In the American vernacular, 'theory' often means 'imperfect fact' —part of a hierarchy of confidence running downhill from fact to theory to hypothesis to guess." 1

    • "A theory is defined ... popularly [as] 'a mere conjecture'." 8

    • In the television programs NYPD Blue, or Law and Order, CSI, etc. a "theory" typically means a hunch by one of the detectives. It may or may not pan out.

  • However, in scientific usage a theory is :
    • ... an established and experimentally verified fact or collection of facts about the world. Unlike the everyday use of the word theory, it is not an unproved idea, or just some theoretical speculation." 9

It is important to differentiate among the terms "hypothesis," "theory," and "law" in science. According to WordNet Search at Princeton University:

bulletAn hypothesis is a tentative insight into the natural world; a concept that is not yet verified but that if true would explain certain facts or phenomena.

bulletA theory is a well-substantiated explanation of some aspect of the natural world; an organized system of accepted knowledge that applies in a variety of circumstances to explain a specific set of phenomena) "theories can incorporate facts and laws and tested hypotheses" 10

The next step is a law:

bullet A law is an explanation of some aspect of the natural world that is so firmly established that it is very unlikely to be changed in the future. Ohm's law that defines the relationship between voltage, current and resistance in metals is one example.

There are many levels of scientific theories. Some, particularly new and emerging theories may be based on little evidence. Others, like the existence of evolution, the laws governing electricity, Newton's laws of motion, genetics etc., are supported by so much evidence from such a wide range of sciences that they are very firmly held beliefs. They have existed for many decades, or even centuries. Some, like the theory of evolution, have been relied upon by generations of physicists, geneticists, cosmologists, biologists, geologists, etc. They are accepted as true facts by essentially all scientists.

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The foundation of science: the scientific method:

It is difficult to comprehend any aspect of science without first understanding the scientific method. This is a very important problem solving technique which has been extensively used by scientists in their quest to build their knowledge base and gradually gain insight into the workings of nature. The scientific method has general application throughout human life as well. 2 It typically involves a number of steps:

bulletObserving something that is unexpected or unusual. Perhaps something that has been detected for the first time.

bulletGathering as much evidence as possible about the phenomenon.

bulletCreating one or more hypotheses that might explain the observation(s), using intuition, analytical methods, trial and error, etc. The hypothesis is based upon the assumption that only natural forces are at work. That is, there are no supernatural forces intruding into the world causing unpredictable results at random times. If such forces did exist, it would make the study of science impossible.

bulletDesigning a test that will give predictable results if the hypothesis is true. (Sometimes the opposite is done: a test is designed to attempt to prove that a hypothesis is false, in order to eliminate it from consideration.)

bulletConducting the test; check the results. Determine if the hypothesis has merit.

bulletRestarting, if the hypothesis has no merit.

bulletIf successful, publishing the results in a peer-reviewed journal.

bulletIndependent duplication of the above steps by others to confirm that the conclusions are reproducible.

At this point, a theory has been discovered. If the theory gains general acceptance in competition with others, then it may become an established theory. Its credibility is improved if it leads to the development of other theories and ultimately to a general advance in scientific knowledge. Established theories are sometimes called "laws," as in Ohms law, Newton's laws (when applied to slow moving objects) and the laws of thermodynamics.

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The importance of falsification of theories and laws:

At any step in the scientific method, falsification is possible: 

bulletThe hypothesis may not be confirmed.
bulletOther scientists may not be able to duplicate the results.
bulletSome new, better, more inclusive theory might come along that replaces the current one.

Implicit in the scientific method is the belief that nothing is absolutely proven for all time. Scientists hold that all truly scientific theories are capable of being falsified. That is, they must always be prepared for some future experiment or investigation that will prove that an existing theory is invalid. The scientific method is thus a self-correcting process; errors will eventually be detected and corrected.

Two well known instances of new evidence that overthrew long established beliefs are:

bulletNewton's Laws: Sir Isaac Newton discovered mathematical formulas that accurately predicted the relationships between applied force, the mass of an object, and its resultant acceleration. These formulas precisely predicted the movement of everything from pendulums to apples to planets. Over time, Newton's theories advanced in status until they became referred to as Newton's Laws. However, in the early 20th century, Einstein developed new equations which predicted that an object's mass is not constant. As its speed approached that of light, its mass increases and dimensions decrease. Subsequent experiments, and observation of naturally occurring phenomena, have validated this theory. However, Newton's Laws are still used in almost all engineering designs because their error is minuscule under normal circumstances.

bulletBacterial cause of ulcers: In the past, doctors had been treating ulcers with stress relief programs, medication to lower stomach acid, and diet. But ulcers often persisted in spite of the best care. Patients often had to accept their condition as permanent. Two Australian physicians were able to demonstrate that many ulcers are not caused by spicy food, excess stomach acid or stress; they were created by a particular bacterium called H.pylori. One of the researchers actually infected himself with H.pylori, developed ulcers, and then cured himself with antibiotics. 3 The present course of treatment calls for doses of two medications: one antibiotic that kills the bacteria, and one that blocks acid. This cures ulcers in over 80% of patients. Although the research was first published in 1983, it was not until 1994 that the U.S. National Institutes of Health endorsed the new treatment. Here, we have an instance where medical science went down the wrong path for many decades. The scientific method played a major role in convincing the medical fraternity to correct their beliefs by accepting a bacterial cause to ulcers.

Sometimes, scientists are reluctant to accept that a theory has been falsified. Too often, they hold tenaciously to older ideas. Einstein's theories were hotly debated until overwhelming proof was obtained through astronomical and other observations. The bacterial origin of most ulcers was resisted by the medical profession because it was so radical. But eventually, accurate theories win out and become generally accepted.

The theory of evolution could theoretically be falsified at any time. Finding absolute evidence of a screwdriver, or the remains of a camp fire, or a human burial site imbedded in a rock layer with trilobite fossils would suggest that major revisions to biological evolutionary beliefs might necessary. Such a discovery would show that some intelligent life forms existed at the same time as trilobites did. Finding a verified human footprint in the middle of a fossilized dinosaur footprint would also throw the theory of evolution into question, unless an alternative explanation could be found. (Many markings resembling human footprints have been found, but all have been shown to be non-human: either pious hoaxes manually carved into rocks to support the faith of believers, or weathered footprints of other animals.)

Creation scientists have developed many indicators that have convinced them that evolution never happened. Some are based on misunderstandings of physics. All can be easily rebutted.

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Is the theory of evolution a scientific theory or an established fact?

It is important to differentiate between:

bullet The broad concept of evolution: The vast majority of scientists have long accepted that the Theory of Evolution broadly describes how animal and plant species grow, develop, and change over time. One source estimates that 0.15% of scientists in the biological and earth science fields believe in creation science; the rest accept that evolution of living species has taken place in the past, and is still in progress.

bulletDetails of evolutionary development: Knowledge of many specific details of evolution are unknown at this time. Details are only gradually being filled in. The full "'truth' can probably never be determined. Results must always be held open to extension, modification, even possible replacement." 2

Many, probably most, scientists believe:

bulletThat biological evolution actually happened; it is a fact.

bulletSome of the precise mechanisms by which it happened are still being debated.

Some leading scientists have commented on the theory of evolution as fact. In his book "Does God Believe in Atheists?" author John Blanchard cites statements by eight leading scientists who agree with the theory. Three are: 4

bulletThe late Carl Sagan went so far as to write that "Evolution is a fact, not a theory," in his printed book which accompanied the Cosmos television series. 5

bulletGeorge Simpson, a famous American zoologist, stated that "Darwin...finally and definitely established evolution as a fact." 6

bulletH.J. Muller, arranged to have 177 leading American biologists sign a manifesto which stated that the organic evolution of all living species is a fact of science that is a well established as the earth is round. 7

In addition:

bulletStephen J Gould, quoted Charles Darwin's book The Descent of Man. Darwin wrote:
"I had two distinct objects in view; firstly, to show that species had not been separately created, and secondly, that natural selection had been the chief agent of change....Hence if I have erred in....having exaggerated its [natural selection's] power....I have at least, as I hope, done good service in aiding to overthrow the dogma of separate creations."
Gould concluded that "...Darwin acknowledged the provisional nature of natural selection while affirming the fact of evolution." 1

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The following information sources were used to prepare and update the above essay. The hyperlinks are not necessarily still active today.

  1. Stephen Jay Gould, "Evolution as Fact and Theory." Published in "Hen's Teeth and Horse's Toes," w.w. Norton, (1994), Pages 254 to 262. Online at:
  2. The Scientific Method: Ingredient #13 at:
  3. "FDA Approves Drugs That Cure Ulcers," Gannett News Service, 1996-AUG-8
  4. John Blanchard, "Does God believe in Atheists?," Evangelical Press, (2000), Pages 83 & 84. Read reviews or order this book safely from online book store
  5. Carl Sagan, "Cosmos," Random House, Page 27.
  6. Quoted in G. Bowden & J. Collyer, "Quotable Quotes for Creationists," Creation Science Movement, Pamphlet # 228, 1982-JAN, Page 1.
  7. H.J. Muller, "Is Biological Evolution a Principle of Nature that has been well established by Science?", 1966-MAY.
  8. Benjamin Wiker, "How dare we question Darwin?," ToTheSource mailing, 2005-MAR-30.
  9. Glossary of scientific terms, What is life, at:
  10. WordNet Search 3.0 for "theory" at:
  11. Edward J. Larson, "Is evolution 'Just a Theory'?" History News Network, 2005-FEB-14, at: http:/

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Copyright 2001 to 2011 by Ontario Consultants on Religious Tolerance
Latest update: 2011-FEB-22
Author: B.A. Robinson

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