Evolution as theory and fact

From Wikipedia, the free encyclopedia

Evolution is often said to be both theory and fact. This statement, or something similar, appears over and over in the biological literature. [1][2][3][4][5][6][7][8][9][10][11][12][13][14]

Unfortunately, this common and seemingly contradictory phrase is a troubling source of confusion. The roots of this confusion are to be found in the different uses of language by lay people, and by scientists.

Contents

[edit] The Terminology of Science

"Fact" "Theory"
A "fact" in science is an observation. A "theory" in science is an explanation for observations.

Scientists use many specialized terms, frequently incorporating terminology that may have different meanings to the lay-person. In defining "fact" and "theory", scientists ascribe to them very distinct meanings:

  • In science, a fact[15] is an observation or a piece of data. A "fact" in science is a measurement or some evidence or the result of an experiment. For example, there are many observations of gravity and measurements of gravity. Every time an apple is dropped and it falls, an observation of gravity has been made. Gravity is measured every time something is weighed. So gravity can be described by scientists as a "fact". This is because there is a collection of gravity observations that need to be explained. And observations are "facts" in scientific language.
  • Theories[16] in science are different from facts. "Theories" in science are the description of the coherent framework into which the observable data fit. There have been many "theories" that attempt to explain the "fact" of "gravity". That is, scientists ask what is gravity, and what causes it? Scientists try to develop a model to explain gravity; this model is called a "theory" of gravity. Predictions can be made based on this "theory" of gravity. There have been many explanations of gravity that qualify as a Theory of Gravity over the centuries; Aristotle's theory of gravity, Galileo's theory of gravity, Newton's theory of gravity and now Einstein's theory of gravity. So gravity is also a "theory". In no case did gravity simply disappear when a new theory was created, only the explanation underlying gravity was refined and improved.

Carefully examining these two descriptions of the words "fact" and "theory" in a scientific context, reveals a source of confusion when discussing gravity. Gravity is referred to as both a "fact" and a "theory". Gravity is a "fact" because it has been observed, and observations are "facts" in scientific language. Gravity is also the name of the explanation for this "fact" and other evidence, or "facts". And scientific explanations are called "theories" in the language of science. So gravity is also a "theory", as well as a "fact".

The word "gravity" has been assigned to two different things, a "theory" and a "fact". It might appear confusing and disingenuous to refer to gravity as both a "theory" and a "fact", but it is accurate. Gravity is an observable "fact". How and why gravity pulls on objects is the subject of a Theory of Gravity. A Theory of Gravity is subject to rigorous scientific study, and it might be replaced with another "theory". It is common to refer to the most widely accepted "theory" of gravity as The Theory of Gravity, although of course it is just one of several. The validity of the statement that gravity exists remains unchanged, no matter what "theory" is most widely accepted, or even if no "theory" exists at that moment.

[edit] Scientific terminology applied to evolution

The terms "fact" and "theory" can be applied to evolution, just as they are to gravity.[1] This terminology has been used to dispute the validity of evolution, which results from a misunderstanding of how those terms are applied to evolution.

In the study of biological species, the "facts" include fossils and measurements of these fossils. The location of a fossil is an example of a "fact" (using the scientific meaning of the word "fact"). In species that rapidly reproduce, for example fruit flies, the process of evolutionary change has been observed in the laboratory.[17][18] The observation of fruit fly populations changing character is also an example of a "fact", using the scientific meaning of the word "fact". So evolution is a "fact", at least using the scientific meaning of the word "fact". These "facts" need an explanation, just like the observations of gravity did.

In biology, there have been many attempts to explain these observations over the years. Lamarckism, Transmutationism and Orthogenesis are all nonDarwinian "theories" (in the scientific sense of the word "theory") that attempt to explain the observations of species and fossils and other evidence. However, the explanation for all these data or "facts" that is currently most accepted by scientists is called the Theory of Evolution. The "theory" of evolution is a model that explains the vast majority of the data, or evidence, that exist. So evolution is not only a "fact" but a "theory", just as gravity is both a "fact" and a "theory".[19]

Gravity Evolution
Things falling is an observation of the pull of bodies towards each other. Fruit flies changing generation to generation is an observation of generational organism change.
Bodies pulling towards each other is called gravity. Organisms changing generation to generation is called evolution.
Gravity is a "fact". Evolution is a "fact".
The "facts" of gravity require an explanation. The "facts" of evolution require an explanation.
Aristotle, Galileo, and Newton created explanations of the "fact" of gravity. These are now obsolete explanations. Lamarckism, Transmutationism and Orthogenesis were created as explanations of the "fact" of evolution. These are now obsolete explanations.
Einstein's explanation is currently the most accepted explanation of the "fact" of gravity Darwin's explanation is currently the most accepted explanation of the "fact" of evolution
Einstein's explanation of the "fact" of gravity is called the Theory of Gravity Darwin's explanation of the "fact" of evolution is called the Theory of Evolution
Gravity is a "fact" and a "theory." Evolution is a "fact" and a "theory."

[edit] Evolution as theory and fact in the literature

This confusion between "fact" and "theory" in the study of evolution was explored in a well-known quote by paleontologist Stephen Jay Gould:

"Evolution is a theory. It is also a fact. And facts and theories are different things, not rungs in a hierarchy of increasing certainty. Facts are the world's data. Theories are structures of ideas that explain and interpret facts. Facts do not go away when scientists debate rival theories to explain them. Einstein's theory of gravitation replaced Newton's, but apples did not suspend themselves in mid-air, pending the outcome. And humans evolved from ape-like ancestors whether they did so by Darwin's proposed mechanism or by some other yet to be discovered."[2]

Similarly, Neil Campbell writes in his 1990 biology textbook,

Today, nearly all biologists acknowledge that evolution is a fact. The term theory is no longer appropriate except when referring to the various models that attempt to explain how life evolves... it is important to understand that the current questions about how life evolves in no way implies any disagreement over the fact of evolution.[4]

Biologist Ernst Mayr states,

The basic theory of evolution has been confirmed so completely that most modern biologists consider evolution simply a fact. How else except by the word evolution can we designate the sequence of faunas and floras in precisely dated geological strata? And evolutionary change is also simply a fact owing to the changes in the content of gene pools from generation to generation.[12]

Biologist Richard Lenski writes,

Scientific understanding requires both facts and theories that can explain those facts in a coherent manner. Evolution, in this context, is both a fact and a theory. It is an incontrovertible fact that organisms have changed, or evolved, during the history of life on Earth. And biologists have identified and investigated mechanisms that can explain the major patterns of change.[9]

This theme arises over and over again in the biological literature in different guises. Carl Sagan wrote "Evolution is a fact, not a theory".[11] American zoologist and paleontologist George Simpson, stated that "Darwin...finally and definitely established evolution as a fact."[13] R. C. Lewontin wrote, "It is time for students of the evolutionary process, especially those who have been misquoted and used by the creationists, to state clearly that evolution is a fact, not theory."[3] Douglas Futuyama writes in his book, "the statement that organisms have descended with modifications from common ancestors--the historical reality of evolution--is not a theory. It is a fact, as fully as the fact of the earth's revolution about the sun."[6] H. J. Muller states, "If you like, then, I will grant you that in an absolute sense evolution is not a fact, or rather, that it is no more a fact than that you are hearing or reading these words."[7] Kenneth R. Miller writes, "evolution is as much a fact as anything we know in science."[20]

In spite of all the enthusiasm evident in these excerpts, considerable confusion remains in some circles.[21][22]

[edit] Related concepts

  • Speculative or conjectural explanations are called hypotheses. Well-tested explanations are called theories.
  • "Theories" are not "true" in science, at least in the regular sense of the word "true". "True" "theories" only are "confirmed to such a degree that it would be perverse to withhold provisional assent." [2]
  • "Proof" of a theory does not exist in science. Proof only exists in mathematics.
  • A scientific law is a concept related to a scientific theory. Very well-established "theories" that rely on a simple principle are often called scientific "laws". For example, it is common to encounter reference to the "law of natural selection" or the "laws of evolution."

[edit] Notes

  1. ^ a b Evolution is a Fact and a Theory, Laurence Moran, Talkorigins, 1993
  2. ^ a b c Stephen J. Gould, " Evolution as Fact and Theory"; Discover, May 1981
  3. ^ a b R. C. Lewontin "Evolution/Creation Debate: A Time for Truth" Bioscience 31, 559 (1981) reprinted in "Evolution versus Creationism,", Peter Zetterberg ed., ORYX Press, Phoenix AZ 1983
  4. ^ a b Neil A. Campbell, Biology 2nd ed., 1990, Benjamin/Cummings, p. 434
  5. ^ Helena Curtis and N. Sue Barnes, Biology 5th ed. 1989, Worth Publishers, p. 972
  6. ^ a b Douglas J. Futuyma, Evolutionary Biology, 2nd ed., 1986, Sinauer Associates, p. 15
  7. ^ a b H. J. Muller, "One Hundred Years Without Darwin Are Enough" School Science and Mathematics 59, 304-305. (1959) reprinted in "Evolution versus Creationism", Peter Zetterberg ed., ORYX Press, Phoenix AZ 1983
  8. ^ Theodosius Dobzhansky "Nothing in Biology Makes Sense Except in the Light of Evolution", American Biology Teacher vol. 35 (March 1973) reprinted in "Evolution versus Creationism", J. Peter Zetterberg ed., ORYX Press, Phoenix AZ 1983
  9. ^ a b "Evolution: Fact and Theory", Richard E. Lenski, American Institute of Biological Sciences, 2000.
  10. ^ Fact and theory misconception, Adrian Barnett
  11. ^ a b Carl Sagan, "Cosmos," Random House, Page 27.
  12. ^ a b Mayr, E. (1988), "Toward a New Philosophy of Biology: Observations of an Evolutionist, Harvard University Press, Cambridge MA USA.
  13. ^ a b George Simpson, a famous American zoologist, stated that "Darwin...finally and definitely established evolution as a fact," quoted in G. Bowden & J. Collyer, "Quotable Quotes for Creationists," Creation Science Movement, Pamphlet # 228, 1982-JAN, Page 1.
  14. ^ H.J. Muller, "Is Biological Evolution a Principle of Nature that has been well established by Science?", 1966-MAY: 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.
  15. ^ A scientific "fact" is obtained by objective observation or measurement, usually under controlled conditions. However, a "fact" does not mean absolute certainty in science. In science, "facts" can have error bars due to measurement errors.
  16. ^ A "theory" is an attempt to identify and describe relationships between phenomena or things, and generates falsifiable predictions which can be tested through controlled experiments and empirical observation.
  17. ^ T. Dobzhansky, & O. Pavlovsky, "An experimentally created incipient species of Drosophilia", Nature 23, P. 289-292 (1971)
  18. ^ The fish tilapia has also been observed to evolve in the field (Franck et al, 1990; M. Losseau-Hoebeke, 1992).
  19. ^ Fact and theory denote the epistemological status of knowledge; that is, how the knowledge was obtained, what sort of knowledge it is. For more information, see the article on physical law.
  20. ^ "Finding Darwin's God: A Scientist's Search for Common Ground Between God and Evolution," Kenneth R. Miller, Cliff Street Books, HarperCollins, New York, NY USA, 1999.
  21. ^ State of Oklahoma. 2003. House Bill HB1504: Schools; requiring all textbooks to have an evolution disclaimer; codification; effective date; emergency. states that evolution is "just a theory".
  22. ^ Refuting Evolution II, Jonathan Sarfati, Michael Matthews, Master Books, a division of New Leaf Press, Green Forest, Arkansas, 2002.

[edit] References

  • J.P. Franck, et. al., "Evolution of a satellite DNA family in tilapia." Annual Meeting Canadian Federation of Biological Societies. Halifax, (1990).
  • M. Losseau-Hoebeke, "The biology of four haplochromine species of Lake Kivu (Zaire) with evolutionary implications." Thesis, Dept Ichthyology, Rhodes University, Grahamstown, (1992).

[edit] See also

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