Evolution as theory and fact

Evolution as theory and fact

Evolution is both theory and fact. This statement, or something similar, is frequently seen in biological literature. cite web | url = http://www.talkorigins.org/faqs/evolution-fact.html | title = Evolution is a Fact and a Theory | first = Laurence | last = Moran | publisher = Talk.origins | date =1993-01-22 | accessdate = 2007-10-18 | language = english | format = html ] cite journal | url = http://www.stephenjaygould.org/library/gould_fact-and-theory.html | first = Stephen Jay | last = Gould | authorlink = Stephen Jay Gould | title = Evolution as Fact and Theory | journal = Discover | volume = 2 | issue = 5 | date = 1981-05-01 | pages = 34–37Reprinted in:
*cite book | title = Speak Out Against The New Right | first = Herbert F. (ed.)| last = Vetter | publisher = Beacon Press | year = 1982 | isbn = 0807004863
*cite book | last = Gould | first = Stephen Jay | authorlink = Stephen Jay Gould | title = Hen's Teeth and Horse's Toes | publsher = W. W. Norton & Company | location = New York | date = 1994-04-01 | isbn = 0393017168] cite journal | url= http://www.skepticfiles.org/evolut/100pcnts.htm | first = H. J. | last = Muller | title = One hundred years without Darwin are enough| journal = School Science and Mathematics | volume = 59 | pages = 304–305 | year = 1959

Reprinted in:
*cite book | title = Evolution Versus Creationism: The Public Education Controversy | first = Peter (ed.) | last = Zetterberg | publisher = ORYX Press | location = Phoenix AZ | date = 1983-05-01 | isbn = 0897740610 ] cite book | first = Neil A. | last = Campbell | title = Biology 6th ed. | date = 2002-02-05 | publisher = Benjamin Cummings | pages = 1175 | isbn = 0805366245 | coauthors = Reece, Jane B.] cite journal | first = Theodosius | last = Dobzhansky | authorlink=Theodosius Dobzhansky | url = http://people.delphiforums.com/lordorman/light.htm | title = Nothing in biology makes sense except in the light of evolution | journal = American Biology Teacher | volume = 35 | date = 1973-03-01

Reprinted in:
*cite book | title = Evolution Versus Creationism: The Public Education Controversy | first = Peter (ed.) | last = Zetterberg | publisher = ORYX Press | location = Phoenix AZ | date = 1983-05-01 | isbn = 0897740610 ] cite book | first = Neil A. | last = Campbell | title = Biology 6th ed. | date = 2002-02-05 | publisher = Benjamin Cummings | pages = 1175 | isbn = 0805366245 | coauthors = Reece, Jane B.] cite web | title = Evolution: Fact and Theory | first = Richard E. | last = Lenski | publisher = American Institute of Biological Sciences | url = http://www.actionbioscience.org/evolution/lenski.html | year = 2000 | accessdate = 2007-10-18 | language = english | format = html ] cite book |author=Mayr, Ernst |title=Toward a New Philosophy of Biology: Observations of an Evolutionist |publisher=Harvard University Press |location=Cambridge |year= |pages= |isbn=0-674-89666-1 |oclc= |doi=] The point of this statement is to differentiate the concept of the "fact of evolution", namely the observed changes in populations of organisms over time, from the "theory of evolution", namely the current scientific explanation of how those changes came about.

Evolution, fact and theory

Evolution has often been described as "fact and theory", "fact not theory" and especially by creationists "only a theory, not a fact". Although this is frequently a disagreement over how well the evidence supports each of the various claims made by evolution, the argument has been hampered by terminological confusion. [ [http://www.discovery.org/a/6401 Is "Evolution" a "Theory" or "Fact" or Is This Just a Trivial Game of Semantics?] by Casey Luskin] [ [http://www.csicop.org/specialarticles/terminology.html#author Commitee for Skeptical Inquiry — Evolution & Creationism: Terminology in Conflict] by Richard Joltes] The meanings of the terms "evolution" and "fact" and "theory", as used in the context of this debate, are described below:


Evolution is usually defined simply as changes in trait or gene frequency in a population of organisms from one generation to the next. However, "evolution" is often used to include the following additional claims:

#Differences in trait composition between isolated populations over many generations may result in the origin of new species.
#All living organisms alive today have descended from a common ancestor (or ancestral gene pool).

According to Douglas Futuyma, " 'biological evolution may be slight or substantial; it embraces everything from slight changes in the proportion of different alleles within a population (such as those determining blood types) to the successive alterations that led from the earliest proto-organism to snails, bees, giraffes, and dandelions.' "cite book | first = Douglas J. | last = Futuyma | title = , Evolutionary Biology, 3rd ed. | year = 1997 | publisher = Sinauer Associates | isbn = 0878931899 | pages = 751 ]

The term "evolution", especially when referred to as a "theory", is also used more broadly to incorporate processes such as natural selection and genetic drift.


Fact is often used by scientists to refer to experimental data or objective verifiable observations. "Fact" is also used in a wider sense to mean any hypothesis for which there is overwhelming evidence.

Evolution as theory and fact in the literature

The confusion between "fact" and "theory" and the use of the word "evolution" is largely due to some authors using evolution to refer to the changes that occur within species over generations and common descent, while others use the term more generally to include the mechanisms driving the change. However, among biologists at least, there seems to be consensus that evolution is a fact:

*American zoologist and paleontologist George Simpson stated that " 'Darwin...finally and definitely established evolution as a fact.' "cite web | title = Is the theory of evolution merely a "theory"? | url = http://www.religioustolerance.org/ev_stat.htm | date = 2005-08-30 | last = Robinson | first = B.A. | accessdate = 2007-10-18 | language = english | format = html ]
*H. J. Muller has written, " '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.' "
*Kenneth R. Miller writes, " 'evolution is as much a fact as anything we know in science.' ""cite book |author=Miller, Kenneth S. |title=Finding Darwin's God: A Scientist's Search for Common Ground Between God and Evolution (P.S.) |publisher=Harper Perennial |location=New York, N.Y |year= |pages= |isbn=0061233501 |oclc= |doi=]
*Ernst Mayr has observed " '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" '.

Evolution as fact and theory

Commonly "fact" is used to refer to the observable changes in organisms' traits over generations while the word "theory" is reserved for the mechanisms that cause these changes:

*Paleontologist Stephen Jay Gould writes, " '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.' "
*Similarly, biologist Richard Lenski says " '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.' "

Evolution as fact not theory

Other commentators, focusing on the changes in species over generations and in some cases common ancestry have stressed that evolution is a fact to emphasize the weight of supporting evidence while denying it is helpful to use the term "theory":

*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.' "cite journal | first = R. C. | last = Lewontin | title = Evolution/creation debate: A time for truth | journal = Bioscience | volume = 31 | pages = 559 | year = 1981 Reprinted in:
*cite book | title = Evolution Versus Creationism: The Public Education Controversy | first = Peter (ed.) | last = Zetterberg | publisher = ORYX Press | location = Phoenix AZ | date = 1983-05-01 | isbn = 0897740610 ]
*Douglas Futuyma writes in his Evolutionary Biology 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.' "
*Richard Dawkins says, " 'One thing all real scientists agree upon is the fact of evolution itself. It is a fact that we are cousins of gorillas, kangaroos, starfish, and bacteria. Evolution is as much a fact as the heat of the sun. It is not a theory, and for pity’s sake, let’s stop confusing the philosophically naive by calling it so. Evolution is a fact.' " [ [http://www.naturalhistorymag.com/master.html?http://www.naturalhistorymag.com/1105/1105_feature1.html Natural History article : The Illusion of Design] by Richard Dawkins]
*Neil Campbell wrote 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.' "cite book | first = Neil A. | last = Campbell | title = Biology 6th ed. | date = 2002-02-05 | publisher = Benjamin Cummings | pages = 1175 | isbn = 0805366245 | coauthors = Reece, Jane B.]

Objections to the fact of evolution

There are those that refuse to accept evolution as fact. House Bill HB1504, in the Oklahoma state legislature, provides a requirement for an "evolution disclaimer" in state-approved textbooks stating that evolution is a "controversial theory" and that "any statement about life’s origins should be considered as theory, not fact." [ [http://www2.lsb.state.ok.us/2003-04hb/hb1504_int.rtf State of Oklahoma. 2003. House Bill HB1504: Schools; requiring all textbooks to have an evolution disclaimer; codification; effective date; emergency.] ] .The creationist website Answers in Genesis claims that evolution should not be classed as a "theory" in the proper scientific sense; rather, they claim that "it would be better to say that particles-to-people evolution is an unsubstantiated hypothesis or conjecture." [ [http://www.answersingenesis.org/home/area/RE2/chapter3.asp "Refuting Evolution II", Jonathan Sarfati, Michael Matthews, Master Books, a division of New Leaf Press, Green Forest, Arkansas, 2002.] ]

The issue was brought before the courts In 1986, when an amicus curiae brief asking the US Supreme Court to reject a Louisiana state law requiring the teaching of creationism in the case Edwards v. Aguillard was signed by 72 US Nobel Prize winners, 17 state academies of science and 7 other scientific societies. The brief provides a detailed argument which it summarises in the following statement.Amicus Curiae brief in cite court |litigants=Edwards v. Aguillard |vol=85-1513|reporter= |opinion= |pinpoint= |court=United States Supreme Court |date=1986-08-18 |url=, available at cite web | url = http://www.talkorigins.org/faqs/edwards-v-aguillard/amicus1.html | title = Edwards v. Aguillard: Amicus Curiae Brief of 72 Nobel Laureates| language = english | format = html | accessdate = 2007-10-19| publisher = From Talk.origins]

The Act's unconstitutional purpose is also evident in its requirement that both "creation-science" and "evolution-science" be taught as "theory" and not as "proven scientific fact." To a scientist or a science educator, the distinction between scientific theories and scientific facts is well understood. A "fact" is a property of a natural phenomenon. A "theory" is a naturalistic explanation for a body of facts. That distinction permeates all fields of scientific endeavor. It is no more relevant to discussions of the origin of the universe and life than to any other area of research. By singling out one topic in science – "origins" – for special treatment, the legislature conveys the false message that the prevailing theory of "origins" – evolutionary theory – is less robust and reliable than all other scientific concepts. This misleadingly disparaging treatment of evolution confirms that the Act favors a particular religious belief.

Predictive power

A central tenet in science is that a scientific theory is supposed to have predictive power, and verification of predictions are seen as an important and necessary support for the theory. The theory of evolution did provide such predictions. Two examples are:

* Genetic information must be transmitted in a molecular way that will be almost exact but permit slight changes. Since this prediction was made, biologists have discovered the existence of DNA, which has a mutation rate of roughly 10−9 per nucleotide per cell division; this provides just such a mechanism.Citation |author1=Bruce Alberts |author1-link=Bruce Alberts |author2=Alexander Johnson |author3=Julian Lewis |author4=Martin Raff |author5=Keith Roberts |author6=Peter Walter |author6-link=Peter Walter |title=Molecular Biology of the Cell |edition=4th |publisher=Routledge |date=March, 2002 |binding=hardcover |totalpages=1616 |weight=7.6 pounds |isbn=0-8153-3218-1]

*Some DNA sequences are shared by very different organisms. It has been predicted by the theory of evolution that the differences in such DNA sequences between two organisms should roughly resemble both the biological difference between them according to their anatomy and the time that had passed since these two organisms have separated in the course of evolution, as seen in fossil evidence. The rate of accumulating such changes should be low for some sequences, which code for critical RNA or proteins, and high for others - that code for less critical RNA or proteins; but for every specific sequence, the rate of change should be roughly constant through evolution. These results have been experimentally confirmed. Two examples are DNA sequences coding for rRNA which is highly conserved, and DNA sequences coding for fibrinopeptides (amino acid chains which are discarded during the formation of fibrin), which are highly non-conserved.

Related concepts and terminology

*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."

*"Proof" of a theory does not exist in science. Proof only exists in mathematics. Experimental observation of the predictions made by a hypothesis or theory is called "validation".

*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 gravity", "the law of natural selection", or the "laws of evolution."

ee also

* Theory vs. Fact (in Creation-evolution controversy)
* Evolution is just a theory, not a fact (in objections to evolution)
*Misconceptions about evolution (in List of misconceptions)
*Evidence of common descent



* 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).

External links

* [http://www.notjustatheory.com Not Just a Theory] Discredits the assertion that evolution is "just a theory", with an explanation of the meaning of the word 'theory' in a scientific context.
* [http://www.re-discovery.org/ Parody website satirizing theory and fact statements]
* [http://www.talkorigins.org/indexcc/CB/CB910.html Talk Origins] Response to the claim that no examples of speciation have been observed.

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