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Evolution as fact and theory

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Evolution as fact and theory

Many scientists and philosophers of science have described evolution as fact and theory, a phrase which was used as the title of an article by common descent, and from transitions in the fossil record. Theories of evolution provide a provisional explanation for these facts.[1]

Each of the words 'evolution', 'fact' and 'theory' has several meanings in different contexts. Evolution means change over time, as in gene frequency over time; it can also refer to explanatory theories such as Darwin's theory of natural selection which explain the mechanisms of evolution. Fact can mean to a scientist a repeatable observation that all can agree on; it can mean something that is so well established that nobody in a community disagrees with it; it can also refer to the truth or falsity of a proposition. To the public, theory can mean an opinion or conjecture ("it's only a theory"), but in the scientific world it has a much stronger connotation of "well-substantiated explanation". With this number of choices, people often end up talking past each other, and meanings become the subject of linguistic analysis.

Evidence for evolution continues to be accumulated and tested. The scientific literature includes statements by evolutionary biologists and philosophers of science demonstrating some of the different perspectives on evolution as fact and theory.


  • Evolution, fact and theory 1
    • Evolution 1.1
    • Fact 1.2
    • Theory 1.3
  • Evolution as theory and fact in the literature 2
    • Evolution as fact 2.1
    • Evolution as fact and theory 2.2
    • Evolution as fact not theory 2.3
    • Evolution as a collection of theories not fact 2.4
  • Related concepts and terminology 3
  • See also 4
  • Notes 5
  • References 6
  • External links 7

Evolution, fact and theory

Evolution has been described as "fact and theory", "fact not theory", "only a theory, not a fact", "multiple theories, not fact", and "neither fact, nor theory".[2] The disagreements among these statements, however, have more to do with the meaning of words than the substantial issues and these are discussed below.


Jerry Coyne sums up biological evolution succinctly:

Life on Earth evolved gradually beginning with one primitive species--perhaps a self-replicating molecule--that lived more than 3.5 billion years ago; it then branched out over time, throwing off many new and diverse species; and the mechanism for most (but not all) of evolutionary change is natural selection.[3]

This shows the breadth and scope of the issue, incorporating the scientific fields of zoology, botany, genetics, geology, paleontology, among many others.

But the central core of evolution is generally defined as changes in trait or Gregor Mendel's research on the inheritance of simple trait variations in peas.[5] Subsequent work into genetics, mutation, paleontology, and developmental biology expanded the applicability and scope of Darwin's original theory.

According to Douglas Futuyma:

Biological evolution may be slight or substantial; it embraces everything from slight changes in the proportion of different [6]

The word evolution in a broad sense refers to processes of change, from

  • Evolutionary theory An international journal of fact and interpretation
  • 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.
  • Talk Origins Response to the claim that no examples of speciation have been observed.
  • Glenn Branch; Louise S. Mead (2008). ""Theory" in Theory and Practice". Evo Edu Outreach 1 (3): 287–289.  

External links

  • Bell, G. (2008). Selection: The mechanism of evolution (2nd ed.). Oxford University Press.  
  • Fitzhugh, K. (2006). "The abduction of phylogenetic hypotheses". Zootaxa (Magnolia Press) 1145: 1–110.  
  • Fitzhugh, K. (2007). "Fact, theory, test and evolution". Zoological Scripta 37 (1): 109–113.  
  • Futuyma, Douglas (1998). Evolutionary Biology (3rd ed. ed.). Sinauer Associates. pp. 9–12. 
  • Kluge, A. G. "The science of phylogenetic systematics: Explanation, prediction, and test". cladistics 15: 429–436.  
  • Laurin, M.; Girondot, M.; de Ricqlès, A. (2000). "Early tetrapod evolution". Trends in Ecology & Evolution 15 (3): 118–123.  
  • Lenski, Richard E. (2000). "Evolution: Fact and Theory". American Institute of Biological Sciences. Retrieved 2007-10-18. 
  • Lombrozo, T.; Thanukos, A.; Weisberg, M. (2008). "The importance of understanding the nature of science for accepting evolution". Evo Edu Outreach 1: 290–298.  
  • Mayr, Ernst (1988). Toward a New Philosophy of Biology: Observations of an Evolutionist. Cambridge: Harvard University Press.  
  • Moran, Laurence (1993-01-22). "Evolution is a Fact and a Theory".  
  • Moran, Laurence (1993-01-22). "What is Evolution?".  
  • Muller, H. J. (1959). "One hundred years without Darwin are enough". School Science and Mathematics 59 (4): 304–305.   Reprinted in: Zetterberg 1983
  • National Academy of Sciences and Institute of Medicine (2008). Science, Evolution, and Creationism. National Academy Press.  
  • Rykiel, E. J. (1996). "Testing ecological models: the meaning of validation". Ecological Modelling 90 (3): 229–244.  
  • Wilson, E. O. (1999). Consilience: The Unity of Knowledge. Vintage. p. 384.  
  • Zetterberg, Peter (ed.) (1983-05-01). Evolution Versus Creationism: The Public Education Controversy. Phoenix AZ: ORYX Press.  


  1. ^  
  2. ^ See section 3
  3. ^  
  4. ^ Mayr, Ernst (1982). The Growth of Biological Thought: Diversity, Evolution, and Inheritance. Harvard University Press, Cambridge, MA. p. 400. 
  5. ^ Wright, S. (1968). Evolution and the Genetics of Populations: Genetics and Biometric Foundations 1. The University of Chicago Press.  
  6. ^ Futuyma 1997
  7. ^ Moran 1993a
  8. ^ Thomson, Keith Stewart (1982). "The meanings of evolution". American Scientist 70: 529–531.  
  9. ^ Thomson 1982
  10. ^ a b Moran 1993
  11. ^ Spencer, Herbert (1857). "Progress: its Law and Cause". Westminster Review: 446. 
  12. ^ Spencer, Herbert (1857). First Principles of a New System of Philosophy. p. 176. 
  13. ^ James, William (1911). "Herbert Spencer's Autobiography". Memories and Studies. 
  14. ^ Brady, Michael (2012). "Evolutionary Opponents: William James and Herbert Spencer". Society for the Advancement of American Philosophy Conference. Retrieved 10 June 2013. 
  15. ^ """WordNet Search - 3.1: "scientific fact. Retrieved 2013-02-21. 
  16. ^ "United States National Park Service Glossary". Retrieved 2013-02-21. 
  17. ^ Webster's Encyclopedic Unabridged Dictionary of the English Language (1996) gives a third meaning of the word "fact" as (3) A truth known by actual experience or observation; something known to be true: 'Scientists gather facts about plant growth.'
  18. ^ a b Futuyma 1998
  19. ^ Dawkins, Richard; Coyne, Jerry (September 1, 2005). "One side can be wrong". The Guardian.
  20. ^ Muller 1959
  21. ^ Science and Creationism: A View from the National Academy of Sciences, Second Edition. (1999), National Academy of Sciences (NAS), National Academy Press, Washington DC, 2006.
  22. ^ Gould 1981 citing Darwin, Charles (1871). The Descent of Man. p. 152. 
  23. ^ Wilkins, JS (1997). "Evolution and Philosophy:Is Evolution Science, and What Does 'Science' Mean?". The TalkOrigins Archive]. Retrieved 2009-08-17. 
  24. ^ National Academy of Sciences, 1999
  25. ^ van Wyhe, J. (2007). "Mind the gap: did Darwin avoid publishing his theory for many years?". Notes Rec. R. Soc. 61 (2): 177–205.  
  26. ^ Bock, W. J. (2007). "Explanations in evolutionary theory". J Zool Syst Evol Res 45 (2): 89–103.  
  27. ^ a b Fitzhugh 2007
  28. ^ Wilson 1999
  29. ^ Wiley, E. O.; Lieberman, B. S. (2011). Phylogenetics: Theory and Practice of Phylogenetic Systematics (2nd ed.). p. 300.  
  30. ^ Schuh, R. T. (2000). Biological Biological Systematics: Principles and Applications. p. 256.  
  31. ^ Robinson, B.A. (2005-08-30). "Is the theory of evolution merely a "theory"?". Retrieved 2007-10-18. 
  32. ^ Muller
  33. ^ "Miller, Kenneth S. (2007). Finding Darwin's God: A Scientist's Search for Common Ground Between God and Evolution (P.S.). New York, N.Y: Harper Perennial.  
  34. ^ Mayr 1988
  35. ^ Wells, H. G.; Huxley, Julian; Wells, G. P. (1931), The Science of life, pp. 429, 600 
  36. ^ Gould 1981
  37. ^ Lenski 2000
  38. ^ Gregory, T. Ryan (2007). "Evolution as Fact, Theory, and Path". Evolution: Education and Outreach 1 (1): 46–52.  
  39. ^ Lewontin, R. C. (1981). "Evolution/Creation Debate: a time for truth". BioScience 31: 559.   Reprinted in:
    • Zetterberg, Peter, ed. (1983-05-01). Evolution Versus Creationism: the public education controversy. Phoenix AZ: Oryx Press.  
  40. ^ Futuyma, Douglas J. (1997). , Evolutionary Biology, 3rd ed. Sinauer Associates. p. 751.  
  41. ^ Natural History article : The Illusion of Design by Richard Dawkins
  42. ^ Campbell, Neil A.; Reece, Jane B. (2002-02-05). Biology 6th ed. Benjamin Cummings. p. 1175.  
  43. ^ "Recent Research by J. Kirk Fitzhugh, Ph.D.". Natural History Museum of Los Angeles County. Retrieved February 14, 2014.
  44. ^ Bell 2008, p. 1
  45. ^ Sundholm, G. "Proof-Theoretical Semantics and Fregean Identity Criteria for Propositions". The Monist 77 (3): 294–314.  
  46. ^ Bissell, D. (1996). "Statisticians have a Word for it". Teaching Statistics 18 (3): 87–89.  
  47. ^ Gould 2002
  48. ^ Bell 2008, p. 492
  49. ^ Platt, J. R. (1964). "Strong inference". Science 146 (3642): 347–353.  
  50. ^ Gorelic, R. (2011). "What is theory?". Ideas in Ecology and Evolution 4: 1–10.  
  51. ^ Godfrey-Smith, P. (2006). "The strategy of model-based science". Biol Philos 21: 725–740.  
  52. ^ Rykiel 1996, p. 233
  53. ^ Rohlf, F. J.; Chang, W. S.; Socal, R. R.; Kim, J. (1990). "Accuracy of Estimated Phylogenies: Effects of Tree Topology and Evolutionary Model". Evolution 44 (6): 1671–1684.  


See also

  • "Proof" of a theory has different meanings in science. Proof exists in formal sciences, such as a mathematical proof where symbolic expressions can represent infinite sets and scientific laws having precise definitions and outcomes of the terms. Proof has other meanings as it descends from its Latin roots (provable, probable, probare L.) meaning to test.[45][46] In this sense a proof is an inference to the best or most parsimonious explanation through a publicly verifiable demonstration (a test) of the factual (i.e., observed) and causal evidence from carefully controlled experiments. Gould argued that Charles Darwin's research, for example, pointed to the coordination of so many pieces of evidence that no other configuration other than his theory could offer a conceivable causal explanation of the facts. In this way natural selection and common ancestry has been proven.[47] "The classical proof is the improvement of crops and livestock through artificial selection."[48] Natural selection and other evolutionary theories are also represented in various mathematical proofs, such as the Price equation. To remain consistent with the philosophy of science, however, advancement of theory is only achieved through disproofs of hypotheses.[49]
  • "Models" are part of the scientific or inferential "tool-kit" that are constructed out of preexistent theory. Model-based science uses idealized structures or mathematical expressions to strategically create simpler representations of complex worldly systems. Models are designed to resemble the relevant aspects of hypothetical relations in the target systems under investigation.[50][51]
  • "Validation is a demonstration that a model within its domain of applicability possesses a satisfactory range of accuracy consistent with the intended application of the model."[52] Models are used in simulation research. For example, evolutionary phylogeneticists run simulations to model the tree like branching process of lineages over time. In turn, this is used to understand the theory of phylogenetics and the methods used to test for relations among genes, species, or other evolutionary units.[53]

To explain means to identify a mechanism that causes evolution, and to demonstrate the consequences of its operation. These consequences are then the general laws of evolution, of which any given system or organism is a particular outcome.[44]

Related concepts and terminology

  • Evolutionary biologist [27]

Evolution as a collection of theories not fact

  • 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."[39]
  • [40]
  • 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."[41]
  • 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."[42]

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":

Evolution as fact not theory

  • Writing in 1930, biologist Julian Huxley entitled the 3rd book of the wide-ranging series The Science of Life, which dealt with the fossil record and the evidence of plant and animal structures, "The Incontrovertible Fact of Evolution". He also says "Natural Selection is not a theory but a fact. But does it...suffice to account for the whole spectacle of Evolution?...There we come to speculative matters, to theories." But he concludes that "the broad positions of Darwinism emerge from a scrutiny of the most exacting sort, essentially unchanged."[35] In 1932, a portion of the book was republished under the title "Evolution, Fact and Theory".
  • 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."[36]
  • Similarly, biologist [37]
  • Biologist T. Ryan Gregory says, "biologists rarely make reference to 'the theory of evolution,' referring instead simply to 'evolution' (i.e., the fact of descent with modification) or 'evolutionary theory' (i.e., the increasingly sophisticated body of explanations for the fact of evolution). That evolution is a theory in the proper scientific sense means that there is both a fact of evolution to be explained and a well-supported mechanistic framework to account for it."[38]

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:

Evolution as fact and theory

  • American zoologist and paleontologist [31]
  • H. J. Muller wrote, "So enormous, ramifying, and consistent has the evidence for evolution become that if anyone could now disprove it, I should have my conception of the orderliness of the universe so shaken as to lead me to doubt even my own existence. 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."[32]
  • Kenneth R. Miller writes, "evolution is as much a fact as anything we know in science."[33]
  • Ernst Mayr 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."[34]

Evolution as fact

The following sections provide specific quotable references from evolutionary biologists and philosophers of science demonstrating some of the different perspectives on evolution as fact and theory.

Evolution as theory and fact in the literature

Phylogenetic theory is an example of evolutionary theory. It is based on the evolutionary premise of an ancestral descendant sequence of genes, populations, or species. Individuals that evolve are linked together through historical and genealogical ties. Evolutionary trees are hypotheses that are inferred through the practice of phylogenetic theory. They depict relations among individuals that can speciate and diverge from one another. The evolutionary process of speciation creates groups that are linked by a common ancestor and all its descendants. Species inherit traits, which are then passed on to descendants. Evolutionary biologists use systematic methods and test phylogenetic theory to observe and explain changes in and among species over time. These methods include the collection, measurement, observation, and mapping of traits onto evolutionary trees. Phylogenetic theory is used to test the independent distributions of traits and their various forms to provide explanations of observed patterns in relation to their evolutionary history and biology.[29][30] The neutral theory of molecular evolution is used to study evolution as a null model against which tests for natural selection can be applied.

Since Darwin, evolution has become a well-supported body of interconnected statements that explains numerous empirical observations in the natural world. Evolutionary theories continue to generate testable predictions and explanations about living and fossilized organisms.[27][28]

  1. populations changing over generations
  2. gradual change
  3. speciation
  4. natural selection
  5. common descent[26]

The "theory of evolution" is actually a network of theories that created the research program of biology. Charles Darwin, for example, proposed five separate theories in his original formulation, which included mechanistic explanations for:

However, in science, the meaning of theory is more rigorous. A scientific theory is "a well-substantiated explanation of some aspect of the natural world, based on a body of facts that have been repeatedly confirmed through observation and experiment."[24] Theories are formed from hypotheses that have been subjected repeatedly to tests of evidence which attempt to disprove or falsify them. In the case of evolution through natural selection, Darwin conceived the hypothesis around 1839, and made a first draft of the concept three years later in 1842. He discussed this widely with many of his intellectual companions, and conducted further research in the background to his other writings and work. After years of development, he finally published his evidence and theory in On the Origin of Species in 1859.[25]

The scientific definition of the word "theory" is different from the colloquial sense of the word. In the vernacular, "theory" can refer to guesswork, a simple conjecture, an opinion, or a speculation that does not have to be based on facts and need not be framed for making testable predictions.


Philosophers of science argue that we do not know mind-independent empirical truths with absolute certainty: even direct observations may be "theory laden" and depend on assumptions about our senses and the measuring instruments used. In this sense all facts are provisional.[10][23]

A common misconception is that evolution cannot be observed because it all happened millions of years ago and the science does not therefore depend on facts (in the initial sense above). However both biogeographical distribution of species in the Amazon and Malay Archipelago. In the early twentieth century, population genetics had centre stage, and more recently DNA has become the main focus of observation and experimentation.

Gould also points out that "Darwin continually emphasized the difference between his two great and separate accomplishments: establishing the fact of evolution, and proposing a theory—natural selection—to explain the mechanism of evolution."[22] These two aspects are frequently confused. Scientists continue to argue about particular explanations or mechanisms at work in specific instances of evolution, but the fact that evolution has occurred and is still occurring is undisputed.

Scientists most often use the word "fact" to describe an observation. But scientists can also use fact to mean something that has been tested or observed so many times that there is no longer a compelling reason to keep testing or looking for examples. The occurrence of evolution in this sense is fact. Scientists no longer question whether descent with modification occurred because the evidence is so strong.[21]

The National Academy of Science (U.S.) makes a similar point:

There is no sharp line between speculation, hypothesis, theory, principle, and fact, but only a difference along a sliding scale, in the degree of probability of the idea. When we say a thing is a fact, then, we only mean that its probability is an extremely high one: so high that we are not bothered by doubt about it and are ready to act accordingly. Now in this use of the term fact, the only proper one, evolution is a fact.[20]

Evolution is a fact in the sense that it is overwhelmingly validated by the evidence. Frequently, evolution is said to be a fact in the same way as the Earth revolving around the Sun is a fact.[18][19] The following quotation from H. J. Muller, "One Hundred Years Without Darwin Are Enough" explains the point.

A fact is a hypothesis that is so firmly supported by evidence that we assume it is true, and act as if it were true. —Douglas Futuyma[18]

Fact is often used by scientists to refer to experimental or empirical data or objective verifiable observations.[15][16] "Fact" is also used in a wider sense to mean any theory for which there is overwhelming evidence.[17]


[14][13] and others.William James but it remained popular throughout the nineteenth century before declining under the criticisms of [12] Even Spencer by 1865 was admitting that his definition was imperfect,[11] used by biologists today. In 1857, the philosopher not that is evolution There is a fourth meaning for the word

Biologists consider it to be a scientific fact that evolution has occurred in that modern organisms differ from past forms, and evolution is still occurring with discernible differences between organisms and their descendants. There is such strong quantitative support for the second that scientists regard common descent as being as factual as the understanding that in the Solar System the Earth orbits the Sun, although the examination of the fundamentals of these processes is still in progress. There are several theories about the mechanisms of evolution, and there are still active debates about specific mechanisms.[10]

Thomson remarks: "Change over time is a fact, and descent from common ancestors is based on such unassailable logic that we act as though it is a fact. Natural selection provides the outline of an explanatory theory."[9]

  1. The general sense of change over time.
  2. All life forms have descended with modifications from ancestors in a process of common descent.
  3. The cause or mechanisms of these process of change, that are examined and explained by evolutionary theories.

The word evolution has at least three distinct meanings:[8]


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