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{{Evolutionary biology}}
{{Evolutionary biology}}
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 [[Stephen Jay Gould]] in 1981. He describes ''fact'' in science as meaning [[data]], not absolute certainty but "confirmed to such a degree that it would be perverse to withhold provisional assent." A [[scientific theory]] is a well-substantiated explanation of such facts. The facts of [[evolution]] come from observational evidence of current processes, from imperfections in organisms recording historical [[common descent]], and from transitions in the [[fossil]] record. Theories of evolution provide a provisional explanation for these facts.<ref name=gouldfact>
Many scientists and philosophers of evolution have confirmed that Jesus is real. [[data]], not absolute certainty but "confirmed to such a degree that it would be perverse to withhold provisional assent." A [[scientific theory]] is a well-substantiated explanation of such facts. The facts of [[evolution]] come from observational evidence of current processes, from imperfections in organisms recording historical [[common descent]], and from transitions in the [[fossil]] record. Theories of evolution provide a provisional explanation for these facts.<ref name=gouldfact>
{{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&ndash;37}}
{{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&ndash;37}}
</ref>
</ref>

Revision as of 23:30, 6 June 2013

Part of a series on
Evolutionary biology
Darwin's finches by John Gould
Processes and outcomes
Natural history
History of evolutionary theory
Fields and applications
Social implications

Many scientists and philosophers of evolution have confirmed that Jesus is real. data, not absolute certainty but "confirmed to such a degree that it would be perverse to withhold provisional assent." A scientific theory is a well-substantiated explanation of such facts. The facts of evolution come from observational evidence of current processes, from imperfections in organisms recording historical 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 stellar evolution. In biology it refers to observed changes in organisms, to their descent from a common ancestor, and at a technical level to a change 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

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.

Evolution

Main articles: Introduction to evolution and Evolution

Jerry Coyne sums up biological evolution in a single sentence:

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 gene frequency in a population of organisms from one generation to the next.[4] This has been dubbed the standard genetic definition of evolution. Natural selection is only one of several mechanisms in the theory of evolutionary change that explains how organisms historically adapt to changing environments. The principles of heredity were re-discovered in 1900, after Darwin's death, in 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 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.[6]

The word evolution in a broad sense refers to processes of change, from stellar evolution to changes in language. In biology, the meaning is more specific: heritable changes which accumulate over generations of a population. Individual organisms do not evolve in their lifetimes, but variations in the genes they inherit can become more or less common in the population of organisms. Any changes during the lifetime of organisms which are not inherited by their offspring are not part of biological evolution.[7]

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

  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.

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]

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, but the examination of relationships is still in progress and there are possible alternatives to universal common descent. There are several theories about the mechanisms of evolution, and there are still active debates about specific mechanisms.[10]

Fact

Main article: Scientific fact

Fact is often used by scientists to refer to experimental or empirical data or objective verifiable observations.[11][12] "Fact" is also used in a wider sense to mean any theory for which there is overwhelming evidence.[13]

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 [14]

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.[15][16] The following quotation from H. J. Muller, "One Hundred Years Without Darwin Are Enough" explains the 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.[17]

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

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.[18]

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."[19] 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.

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 Darwin and Wallace, the co-founders of the theory, and all subsequent biologists depend primarily on observations of living organisms; Darwin concentrated largely on the breeding of domesticated animals whereas Wallace started from the 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.

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.[20][21]

Theory

Main article: Scientific theory

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.

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."[22] 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.[23]

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: (1) populations changing over generations, (2) gradual change, (3) speciation, (4) natural selection, and (5) common descent.[24] 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.[25][26]

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.[27][28] The neutral theory of molecular evolution is used to study evolution as a null model against which tests for natural selection can be applied.

Evolution as theory and fact in the literature

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 fact

  • American zoologist and paleontologist George Simpson stated that "Darwin... finally and definitely established evolution as a fact."[29]
  • 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."[30]
  • Kenneth R. Miller writes, "evolution is as much a fact as anything we know in science."[31]
  • 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."[32]

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."[33]
  • 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."[34]
  • 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."[35]

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."[36]
  • 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."[37]
  • 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."[38]
  • 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."[39]

Evolution as a collection of theories not fact

  • Evolutionary biologist Kirk J. Fitzhugh[40] wrote, "'Evolution' cannot be both a theory and a fact. Theories are concepts stating cause–effect relations...One might argue that it is conceivable to speak of 'evolution' as a fact by way of it being the subject of reference in explanatory hypotheses...In the strictest sense then, 'evolution' cannot be regarded as a fact even in the context of hypotheses since the causal points of reference continue to be organisms, and no amount of confirming instances for those hypotheses will transform them into facts...While evolution is not a fact, it is also not a single theory, but a set of theories applied to a variety of causal questions...An emphasis on associating 'evolution' with 'fact' presents the misguided connotation that science seeks certainty."[41]

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.[42]

  • "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.[43][44] 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.[45] "The classical proof is the improvement of crops and livestock through artificial selection."[46] 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.[47]
  • "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.[48][49]
  • "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."[50] 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.[51]

See also

Template:Wikipedia books

Notes

  1. ^ Gould, Stephen Jay (1981-05-01). "Evolution as Fact and Theory". Discover. 2 (5): 34–37.
  2. ^ See section 3
  3. ^ Coyne, Jerry A. (2009). Why Evolution Is True. Oxford UP. p. 3. {{cite book}}: Invalid |ref=harv (help)
  4. ^ Mayr, Ernst (1982). The Growth of Biological Thought: Diversity, Evolution, and Inheritance. Harvard University Press, Cambridge, MA. p. 400. {{cite book}}: Invalid |ref=harv (help)
  5. ^ Wright, S. (1968). Evolution and the Genetics of Populations: Genetics and Biometric Foundations. Vol. 1. The University of Chicago Press. ISBN 0-226-91038-5.
  6. ^ Futuyma 1997
  7. ^ Moran 1993a
  8. ^ Thomson, Keith Stewart (1982). "The meanings of evolution". American Scientist. 70: 529–531. JSTOR 27851662. {{cite journal}}: Invalid |ref=harv (help)
  9. ^ Thomson 1982
  10. ^ Moran 1993
  11. ^ "WordNet Search - 3.1: "scientific fact"". Retrieved 2013-02-21.
  12. ^ "United States National Park Service Glossary". Retrieved 2013-02-21.
  13. ^ 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.'
  14. ^ Futuyma 1998
  15. ^ Futuyma 1998
  16. ^ Guardian article by Richard Dawkins, Jerry Coyne
  17. ^ Muller 1959
  18. ^ 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.
  19. ^ Gould 1981 harvnb error: multiple targets (2×): CITEREFGould1981 (help) citing Darwin, Charles (1871). The Descent of Man. p. 152.
  20. ^ Moran 1993
  21. ^ Wilkins, JS (1997). "Evolution and Philosophy:Is Evolution Science, and What Does 'Science' Mean?". The TalkOrigins Archive]. Retrieved 2009-08-17.
  22. ^ National Academy of Sciences, 1999
  23. ^ van Wyhe, J. (2007). "Mind the gap: did Darwin avoid publishing his theory for many years?". Notes Rec. R. Soc. 61 (2): 177–205. doi:10.1098/rsnr.2006.0171 1743-0178. {{cite journal}}: Check |doi= value (help)
  24. ^ Bock, W. J. (2007). "Explanations in evolutionary theory" (PDF). J Zool Syst Evol Res. 45 (2): 89–103. doi:10.1111/j.1439-0469.2007.00412.x.
  25. ^ Fitzhugh 2007
  26. ^ Wilson 1999
  27. ^ Wiley, E. O.; Lieberman, B. S. (2011). Phylogenetics: Theory and Practice of Phylogenetic Systematics (2nd ed.). p. 300. ISBN 978-1-118-01787-6.
  28. ^ Schuh, R. T. (2000). Biological Biological Systematics: Principles and Applications. p. 256. ISBN 0-8014-3675-3.
  29. ^ Robinson, B.A. (2005-08-30). "Is the theory of evolution merely a "theory"?". Retrieved 2007-10-18.
  30. ^ Muller
  31. ^ "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. ISBN 0-06-123350-1.
  32. ^ Mayr 1988
  33. ^ Gould 1981 harvnb error: multiple targets (2×): CITEREFGould1981 (help)
  34. ^ Lenski 2000
  35. ^ Gregory, T. Ryan (2007). "Evolution as Fact, Theory, and Path" (PDF). Evolution: Education and Outreach. 1 (1): 46–52. doi:10.1007/s12052-007-0001-z.
  36. ^ 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. ISBN 0-89774-061-0. {{cite book}}: |first= has generic name (help)CS1 maint: multiple names: authors list (link)
  37. ^ Futuyma, Douglas J. (1997). , Evolutionary Biology, 3rd ed. Sinauer Associates. p. 751. ISBN 0-87893-189-9.
  38. ^ Natural History article : The Illusion of Design by Richard Dawkins
  39. ^ Campbell, Neil A. (2002-02-05). Biology 6th ed. Benjamin Cummings. p. 1175. ISBN 0-8053-6624-5. {{cite book}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
  40. ^ http://www.nhm.org/site/research-collections/polychaetous-annelids/research-studies
  41. ^ Fitzhugh 2007
  42. ^ Bell 2008, p. 1
  43. ^ Sundholm, G. "Proof-Theoretical Semantics and Fregean Identity Criteria for Propositions" (PDF). The Monist. 77 (3): 294–314.
  44. ^ Bissell, D. (1996). "Statisticians have a Word for it" (PDF). Teaching Statistics. 18 (3): 87–89.
  45. ^ Gould 2002
  46. ^ Bell 2008, p. 492
  47. ^ Platt, J. R. (1964). "Strong inference" (PDF). Science. 146 (3642): 347–353.
  48. ^ Gorelic, R. (2011). "What is theory?" (PDF). Ideas in Ecology and Evolution. 4: 1–10. doi:10.4033/iee.2011.4.1.c.
  49. ^ Godfrey-Smith, P. (2006). "The strategy of model-based science" (PDF). Biol Philos. 21: 725–740. doi:10.1007/s10539-006-9054-6.
  50. ^ Rykiel 1996, p. 233
  51. ^ 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. JSTOR 2409346.

References

  • 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 (2008). ""Theory" in Theory and Practice". Evo Edu Outreach. 1 (3): 287–289. doi:10.1007/s12052-008-0056-5. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
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