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Species#The species problem

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+#REDIRECT [[Species#The_species_problem]] {{R from merge}}
-The '''species problem''' is the set of questions that arises when [[biologist]]s attempt to define what a [[species]] is. Such a definition is called a '''species concept'''; there are at least 26 recognized species concepts.<ref name=wilkins>{{cite web |url=http://scienceblogs.com/evolvingthoughts/2006/10/01/a-list-of-26-species-concepts/ |title=A List of 26 Species Concepts |publisher=Science Blogs |first=John S. |last=Wilkins |date=1 October 2006}}</ref> A species concept that works well for [[sexual reproduction|sexually reproducing]] organisms such as birds may be useless for species that [[asexual reproduction|reproduce asexually]], such as bacteria. The scientific study of the species problem has been called '''microtaxonomy'''.<ref>{{cite book |author=Mayr, Ernst |author-link=Ernst Mayr |year=1982  |title=The Growth of Biological Thought: Diversity, Evolution, and Inheritance |publisher=Belknap Press of Harvard University Press  |isbn=9780674364462 |chapter-url=https://books.google.com/books?id=pHThtE2R0UQC |chapter=Chapter 6: Microtaxonomy, the science of species}}</ref>
-One common, but sometimes difficult, question is how best to decide which species an [[organism]] belongs to, because reproductively isolated groups may not be readily recognizable, and [[Cryptic species complex|cryptic species]] may be present. There is a continuum from ''[[reproductive isolation]]'' with no interbreeding, to ''[[panmixis]]'', unlimited interbreeding. Populations can move forward or backwards along this continuum, at any point meeting the criteria for one or another species concept, and failing others.
-Many of the debates on species touch on philosophical issues, such as [[nominalism]] and [[Philosophical realism|realism]], and on issues of [[language]] and [[cognition]].
-The current meaning of the phrase "species problem" is quite different from what [[Charles Darwin]] and others meant by it during the 19th and early 20th centuries.<ref>{{cite book |last=Robson |first=G. C. |year=1928 |title=The Species Problem: an Introduction to the Study of Evolutionary Divergence in Natural Populations |publisher=Oliver and Boyd |location=Edinburgh}}</ref> For Darwin, the species problem was the question of [[Speciation|how new species arose]]. Darwin was however one of the first people to question how well-defined species are, given that they constantly change.
-{{Rquote|right|[...] I was much struck how entirely vague and arbitrary is the distinction between species and varieties|[[Charles Darwin]]|''[[On the Origin of Species]]''<ref name="darwin1859">{{cite book |last=Darwin |first=C. |author-link=Charles Darwin |year=1859 |title=On the origin of species by means of natural selection |url=https://archive.org/details/onoriginofspec00darw |publisher=Murray |location=London |isbn=978-84-206-5607-6 |page=[https://archive.org/details/onoriginofspec00darw/page/48 48]}}</ref>}}
-== History ==
-{{main article|Species}}
-=== Before Darwin ===
-The idea that an organism reproduces by giving birth to a similar organism, or producing seeds that grow to a similar organism, goes back to the earliest days of farming. While people tended to think of this as a relatively stable process, many thought that change was possible. The term ''species'' was just used as a term for a sort or kind of organism, until in 1686 [[John Ray]] introduced the biological concept that species were distinguished by always producing the same species, and this was fixed and permanent, though considerable variation was possible within a species.<ref name=SpeciesKindsEvolution>{{cite web |url=http://ncse.com/rncse/26/4/species-kinds-evolution |title=Species, Kinds, and Evolution |author= Wilkins, John S. |year=2006 |publisher=Reports of the [[National Center for Science Education]] |access-date=2009-09-24}}</ref><ref>{{cite web |url=http://scienceblogs.com/evolvingthoughts/2009/05/the_first_biological_species_c.php |title=The first biological species concept : Evolving Thoughts |author=Wilkins, John S. |date=May 10, 2009 |access-date=2009-09-24 |url-status=dead |archive-url=https://web.archive.org/web/20090515041359/http://scienceblogs.com/evolvingthoughts/2009/05/the_first_biological_species_c.php |archive-date=May 15, 2009 }}</ref> [[Carl Linnaeus|Carolus Linnaeus]] (1707–1778) formalized the [[taxon]]omic rank of species, and devised the two part naming system of [[binomial nomenclature]] that we use today. However, this did not prevent disagreements on the best way to identify species.
-The history of definitions of the term ''species''<ref>{{cite journal |last=Britton |first=N.L. |title=The taxonomic aspect of the species question |journal=[[The American Naturalist]] |volume=42 |issue=496 |pages=225–242 |date=April 1908 |doi=10.1086/278927|url=https://zenodo.org/record/1431349 |doi-access=free }}</ref><ref name="mayr1982"/> reveal that the seeds of the modern species debate were alive and growing long before Darwin.
-{{Quote|text=The traditional view, which was developed by [[Arthur Cain|Cain]], [[Ernst Mayr|Mayr]] and [[David Hull|Hull]] in the mid-twentieth century, claims that until the ‘Origin of species’ by Charles Darwin both philosophy and biology considered species as invariable natural kinds with essential features. This ‘[[essentialism]] story’ was adopted by many authors, but questioned from the beginning by a minority … when [[Aristotle]] and the early naturalists wrote about the essences of species, they meant essential ‘functions’, not essential ‘properties’. Richards pointed out [Richard A. Richards, ''The Species Problem: A Philosophical Analysis'', Cambridge University Press, 2010] that Linnaeus saw species as eternally fixed in his very first publication from 1735, but only a few years later he discovered hybridization as a modus for speciation.<ref>{{cite journal |author=Haveman, R. |year=2013 |title=Freakish patterns – species and species concepts in apomicts |journal=Nordic Journal of Botany |volume=31 |issue=3 |pages=257–269 |doi=10.1111/j.1756-1051.2013.00158.x}}</ref>}}
-=== From Darwin to Mayr ===
-[[Charles Darwin]]'s famous book ''[[On the Origin of Species]]'' (1859) offered an explanation as to how species [[evolution|evolve]], given enough time. Although Darwin did not provide details on how species can split into two, he viewed [[speciation]] as a [[gradualism|gradual process]]. If Darwin was correct, then, when new ''incipient species'' are forming, there must be a period of time when they are not yet distinct enough to be recognized as species. Darwin's theory suggested that there was often not going to be an objective fact of the matter, on whether there were one or two species.
-Darwin's book triggered a crisis of uncertainty for some biologists over the objectivity of species, and some came to wonder whether individual species could be objectively real — i.e. have an existence that is independent of the human observer.<ref>{{cite journal |last=Johnson |first=D.S. |date=April 1908 |title=Aspects of the Species Question|journal=[[The American Naturalist]] |volume=42 |issue=496 |page=217 |doi=10.1086/278925|url=https://zenodo.org/record/1431347|doi-access=free }}</ref><ref>{{cite journal |last=Bailey |first=L.H. |date=December 1896 |title=The philosophy of species-making |journal=Botanical Gazette |volume=22 |issue=6 |pages=454–462 |doi=10.1086/327442|s2cid=84976432 |url=https://www.biodiversitylibrary.org/part/222692 }}</ref>
-In the 1920s and 1930s, [[Gregor Mendel|Mendel's]] theory of inheritance and Darwin's theory of evolution by [[natural selection]] were joined in what was called the [[modern synthesis (20th century)|modern synthesis]]. This conjunction of theories also had a large impact on how biologists think about species. [[Edward Bagnall Poulton|Edward Poulton]] anticipated many ideas on species that today are well accepted, and that were later more fully developed by [[Theodosius Dobzhansky]] and [[Ernst Mayr]], two of the architects of the modern synthesis.<ref>{{cite journal |last=Mallet |first=James |author-link=James Mallet |date=December 2003 |title=Perspectives Poulton, Wallace and Jordan: how discoveries in Papilio butterflies led to a new species concept 100 years ago |journal=Systematics and Biodiversity |volume=1 |issue=4 |pages=441–452 |doi=10.1017/S1477200003001300|s2cid=86041887 }}</ref> Dobzhansky's 1937 book<ref name="dobzhansky1937"/> articulated the genetic processes that occur when incipient species are beginning to diverge. In particular, Dobzhansky described the critical role, for the formation of new species, of the evolution of [[reproductive isolation]].
-=== Mayr's ''Biological Species Concept'' ===
-[[Ernst Mayr]]'s 1942 book was a turning point for the species problem.<ref name="mayr1942">{{cite book |last=Mayr |first=Ernst |author-link=Ernst Mayr |year=1942 |title=Systematics and the origin of species from the viewpoint of a zoologist |url=https://archive.org/details/systematicsorigi0000mayr_p8z7 |url-access=registration |publisher=Columbia University Press |location=New York |isbn=978-0-674-86250-0}}</ref> In it, he wrote about how different investigators approach species identification, and he characterized their approaches as species concepts. He argued for what came to be called the ''Biological Species Concept'' (BSC), that a species consists of populations of organisms that can reproduce with one another and that are reproductively isolated from other populations, though he was not the first to define "species" on the basis of reproductive compatibility.<ref name="mayr1982">{{cite book |last=Mayr |first=E. |author-link=Ernst Mayr |year=1982 |title=The Growth of Biological Thought |publisher=Harvard University Press |location=Cambridge, MA |isbn=978-0-674-36445-5|title-link=The Growth of Biological Thought }}</ref> For example, Mayr discusses how [[Georges-Louis Leclerc, Comte de Buffon|Buffon]] proposed this kind of definition of "species" in 1753.
-[[Dobzhansky|Theodosius Dobzhansky]] was a contemporary of Mayr and the author of a classic book about the evolutionary origins of reproductive barriers between species, published a few years before Mayr's.<ref name="dobzhansky1937"/> Many biologists credit Dobzhansky and Mayr jointly for emphasizing reproductive isolation.<ref>{{cite journal |last=Mallet |first=James |author-link=James Mallet |date=November 2001 |title=The speciation revolution |journal=[[Journal of Evolutionary Biology]] |volume=14 |issue=6 |pages=887–888 |url=http://www.ucl.ac.uk/taxome/jim/pap/malletjeb01.pdf |doi=10.1046/j.1420-9101.2001.00342.x|doi-access=free }}</ref><ref>{{cite journal |last=Coyne |first=Jerry |author-link=Jerry Coyne |year=1994 |title=Ernst Mayr and the origin of species |journal=[[Evolution (journal)|Evolution]] |volume=48 |pages=19–30 |doi=10.2307/2409999 |issue=1 |jstor=2409999|pmid=28567778 }}</ref>
-After Mayr's book, some two dozen species concepts were introduced. Some, such as the [[Species#Phylogenetic,_cladistic,_or_evolutionary_species|Phylogenetic Species Concept]] (PSC), were designed to be more useful than the BSC for describing species. Many authors have professed to "solve" or "dissolve" the species problem.<ref name="pigliucci2003"/><ref name="ghiselen1974">{{cite journal |last=Ghiselin |first=Michael |author-link=Michael Ghiselin |date=December 1974 |title=A radical solution to the species problem |journal=Systematic Zoology |volume=23 |issue=4 |pages=536–544 |doi=10.2307/2412471 |jstor=2412471|url=https://philpapers.org/rec/GHIARS }}</ref><ref>{{cite journal |last=de Queiroz |first=K. |date=December 2005 |title=Different species problems and their resolution |journal=[[BioEssays]] |volume=27 |issue=12 |pages=1263–1269 |doi=10.1002/bies.20325 |pmid=16299765}}</ref><ref>{{cite web |last=Hey |first=J. |year=1997 |url=http://lifesci.rutgers.edu/~heylab/sconcept/introduction.html |title=A reduction of "species" and a resolution of the species problem |publisher=[[Rutgers University]], Department of Genetics |access-date=2007-12-25}}</ref><ref>{{cite journal |last=Ridley |first=Mark |author-link=Mark Ridley (zoologist) |date=January 1989 |title=The cladistic solution to the species problem |journal=Biology and Philosophy |volume=4 |issue=1 |pages=1–16 |doi=10.1007/BF00144036|s2cid=84433745 }}</ref><ref>{{cite book |last=Stamos |first=D.N. |year=2003 |title=The species problem: Biological species, ontology, and the metaphysics of biology |publisher=Lexington Books |location=Lanham |isbn=978-0-7391-0503-0}}</ref><ref>{{cite journal |last1=Vrana |first1=P. |last2=Wheeler |first2=W. |year=1992 |title=Individual organisms as terminal entities: Laying the species problem to rest |journal=[[Cladistics (journal)|Cladistics]] |volume=8 |issue=1 |pages=67–72 |doi=10.1111/j.1096-0031.1992.tb00051.x|pmid=34929949 |s2cid=85226463 }}</ref> Some have argued that the species problem is too multidimensional to be "solved" by any one concept.<ref name="heyGCS2001"/><ref>{{cite book |last=Endler |first=J.A. |year=1989 |chapter=Conceptual and other problems in speciation |pages=[https://archive.org/details/speciationitscon0000unse/page/625 625–648] |editor1-last=Otte |editor1-first=D. |editor2-last=Endler |editor2-first=J.A. |title=Speciation and its consequences |publisher=Sinauer Associates |location=Sunderland, Mass. |isbn=978-0-87893-658-8 |chapter-url=https://archive.org/details/speciationitscon0000unse/page/625 }}</ref> Since the 1990s, others have argued that concepts intended to help describe species have not helped to resolve the species problem.<ref name="heyGCS2001">{{cite book |last=Hey |first=J. |year=2001 |title=Genes categories and species |publisher=Oxford University Press |location=New York, NY |isbn=978-0-19-514477-2 |url=https://archive.org/details/genescategoriess01heyj }}</ref><ref>{{cite book |last=de Queiroz |first=K. |year=1998 |chapter=The general lineage concept of species: Species criteria and the process of speciation |pages=[https://archive.org/details/endlessformsspec0000unse/page/57 57–75] |editor1-last=Howard |editor1-first=D.J. |editor2-last=Berlocher |editor2-first=S.H. |title=Endless forms: Species and speciation |publisher=Oxford University Press |location=New York |isbn=978-0-19-510901-6 |chapter-url=https://archive.org/details/endlessformsspec0000unse/page/57 }}</ref><ref>{{cite journal |last=Miller |first=W. |date=December 2001 |title=The structure of species, outcomes of speciation and the 'species problem': Ideas for paleobiology |journal=Palaeogeography, Palaeoclimatology, Palaeoecology |volume=176 |issue=1 |pages=1–10 |doi=10.1016/S0031-0182(01)00346-7|bibcode=2001PPP...176....1M }}</ref><ref>{{cite journal |last=Hey |first=J. |date=August 2006 |title=On the failure of modern species concepts |journal=[[Trends in Ecology & Evolution]] |volume=21 |issue=8 |pages=447–450 |pmid=16762447 |doi=10.1016/j.tree.2006.05.011}}</ref><ref name="Hull-Species">{{cite book |last=Hull |first=D.L. |year=1999 |chapter=On the plurality of species: Questioning the party line |pages=[https://archive.org/details/speciesnewinterd00wils/page/n34 23]–48 |editor-last=Wilson |editor-first=R.A. |title=Species: New Interdisciplinary Essays |url=https://archive.org/details/speciesnewinterd00wils |url-access=limited |publisher=MIT Press |location=Cambridge, MA |isbn=978-0-262-73123-2}}</ref> Although Mayr promoted the BSC for use in [[systematics]], some systematists have criticized it as not [[operational]].<ref name="wheeler2000">{{cite book |last1=Wheeler |first1=QD |last2=Meier |first2=R |year=2000 |title=Species concepts and phylogenetic theory: A debate |publisher=Columbia University Press |location=New York |isbn=978-0-231-10143-1}}</ref><ref>{{cite journal |last1=Zink |first1=R.M. |last2=McKitrick |first2=M.C. |year=1995 |title=The debate over species concepts and its implications for ornithology |journal=[[The Auk]] |volume=112 |issue=3 |pages=701–719}}</ref><ref>{{cite journal |last=Levin |first=D.A. |date=April 1979 |title=The nature of plant species |journal=[[Science (journal)|Science]] |volume=204 |issue=4391 |pages=381–384 |doi=10.1126/science.204.4391.381 |pmid=17757999|bibcode=1979Sci...204..381L |s2cid=85119383 }}</ref><ref>{{cite journal |last1=Sokal |first1=RR |last2=Crovello |first2=TJ |date=March–April 1970 |title=The biological species concept: A critical evaluation |journal=[[The American Naturalist]] |volume=104 |issue=936 |pages=127–153 |doi=10.1086/282646|s2cid=83528114 }}</ref> For others, the BSC is the preferred definition of species. Many geneticists who work on [[speciation]] prefer the BSC because it emphasizes the role of reproductive isolation.<ref>{{cite book |last1=Coyne |first1=Jerry |author-link=Jerry Coyne |last2=Orr |first2=HA |year=2004 |title=Speciation |publisher=Sinauer Associates |location=Sunderland, Mass. |isbn=978-0-87893-089-0}}</ref> It has been argued that the BSC is a natural consequence of the effect of sexual reproduction on the dynamics of natural selection.<ref>Hopf, F.A.; Hopf, F.W. (1985). The role of the Allee effect on species packing.  Theor. Pop. Biol. 27, 27-50.</ref><ref>{{cite journal |authors=Bernstein, H.; Byerly, H.C.; Hopf, F.A.; Michod, Richard E. |title=Sex and the emergence of species |journal=J. Theor. Biol. |volume=117 |issue=4 |pages=665–90 |date=December 1985 |pmid=4094459 |doi= 10.1016/S0022-5193(85)80246-0|bibcode=1985JThBi.117..665B }}</ref><ref>{{cite book |author1=Bernstein, Carol |author2=Bernstein, Harris |title=Aging, sex, and DNA repair |url=https://archive.org/details/agingsexdnarepai0000bern |url-access=registration |publisher=Academic Press |location=Boston |year=1991 |isbn=978-0-12-092860-6}}</ref><ref>{{cite book |author=Michod, Richard E. |title=Eros and evolution: a natural philosophy of sex |url=https://archive.org/details/erosevolutionnat0000mich |url-access=registration |publisher=Addison-Wesley |location=Reading, Mass |year=1995 |isbn=978-0-201-44232-8}}</ref>
-== Philosophical aspects ==
-=== Realism ===
-[[Philosophical realism|Realism]], in the context of the species problem, is the philosophical position that species are real mind-independent entities, [[natural kind]]s. Mayr, a proponent of realism, attempted to demonstrate species exist as natural, extra-mental categories. He showed for example that the New Guinean tribesman classify 136 species of birds, which Western ornithologists came to independently recognize:
-{{Quote|I have always thought that there is no more devastating refutation of the nominalistic claims than the above mentioned fact that primitive natives in New Guinea, with a Stone Age culture, recognize as species exactly the same entities of nature as western taxonomists. If species were something purely arbitrary, it would be totally improbable for representatives of two drastically different cultures to arrive at the identical species delimitations.<ref>{{cite book|title = Toward a New Philosophy of Biology|page = 317|first = Ernst|last = Mayr|publisher = Harvard University Press |date = 1988|isbn = 9780674896666|title-link = Toward a New Philosophy of Biology}}</ref>}}
-Mayr's argument however has been criticized:
-{{Quote|The fact that independently observing humans see much the same species in nature does not show that species are real rather than nominal categories. The most it shows is that all human brains are wired up with a similar perceptual cluster statistic (Ridley, 1993). On this view we [humans] might have been "wired" differently and different species might now be wired differently from us, so that no one wiring can be said to be "true" or "veridical."<ref>Stamos, D. N. (2003). ''The Species Problem''. Lexington Books. p. 95.</ref>}}
-Another position of realism is that natural kinds are demarcated by the world itself by having a unique property that is shared by all the members of a species, and none outside the group. In other words, a natural kind possesses an essential or intrinsic feature (“essence”) that is self-individuating and non-arbitrary. This notion has been heavily criticized as [[essentialism|essentialist]], but modern realists have argued that while biological natural kinds have essences, these need not be fixed and are prone to change through [[speciation]].<ref>Okasha, S. 2002. Darwinian metaphysics: Species and the question of essentialism. ''Synthese''. 131: 191–213.</ref> According to Mayr (1957){{nonspecific|date=July 2021}} reproductive isolation or interbreeding "supplies an objective yardstick, a completely non-arbitrary criterion” and "describing a presence or absence relationship makes this species concept non-arbitrary". The BSC defines species as "groups of actually or potentially interbreeding natural populations, which are reproductively isolated from other such groups".{{cite quote|date=July 2021}} From this perspective, each species is based on a property (reproductive isolation) that is shared by all the organisms in the species that objectively distinguishes them.
-===Nominalism===
-Some philosophical variants of [[nominalism]] propose that species are just names that people have assigned to groups of creatures but where the lines between species get drawn does not reflect any fundamental underlying biological cut-off point. In this view, the kinds of things that people have given names to, do not reflect any underlying reality. It then follows that species do not exist outside the mind, because species are just named abstractions. If species are not real, then it would not be sensible to talk about "the origin of a species" or the "evolution of a species". As recently at least as the 1950s, some authors adopted this view and wrote of species as not being real.<ref>{{cite journal |last=Gregg |first=J.R. |date=November–December 1950 |title=Taxonomy, language and reality |journal=[[The American Naturalist]] |volume=84 |issue=819 |pages=419–435 |doi=10.1086/281639|s2cid=84167383 }}</ref><ref>{{cite book |last=Burma |first=B.H. |year=1954 |chapter=Reality, existence, and classification: A discussion of the species problem |pages=193–209 |editor-last=Slobodchikoff |editor-first=C.N. |title=Concepts of species |publisher=Dowden, Hutchinson & Ross |location=Stroudsburg, PA}}</ref>
-A counterpoint to the nominalist views in regard to species, was raised by [[Michael Ghiselin]] who argued that an individual species is not a type, but rather an actual individual, an actual [[wikt:entity|entity]].<ref name="ghiselen1974"/><ref>{{cite book |last=Ghiselin |first=M.T. |year=1997 |title=Metaphysics and the origin of species |publisher=State University of New York Press |location=Albany, NY |isbn=978-0-7914-3468-0}}</ref> This idea comes from thinking of a species as an evolving dynamic population. If viewed as an entity, a species would exist regardless of whether or not people have observed it and whether or not it has been given a name.
-===Pragmatism===
-A popular alternative view, [[pragmatism]], espoused by philosophers such as [[Philip Kitcher]] and [[John Dupré]] states while species do not exist in the sense of [[natural kind]]s, they are ''[[concept]]ually'' real and exist for convenience and for practical applications.<ref>Dupré, J. (2001). "In defence of classification". ''Studies in History and Philosophy of Biological and Biomedical Sciences''. 32: 203–219.</ref> For example, regardless of which definition of species one uses, one can still quantitatively compare [[species diversity]] across regions or decades, as long as the definition is held constant within a study. This has practical importance in advancing [[biodiversity]] science and [[environmental science]].
-===Language and the role of human investigators===
-The nominalist critique of the view that kinds of things exist, raises for consideration the role that humans play in the species problem. For example, Haldane suggested that species are just mental abstractions.<ref name="haldane1956"/>
-Several authors have noted the similarity between "species", as a word of ambiguous meaning, and points made by [[Wittgenstein]] on [[family resemblance]] concepts and the indeterminacy of language.<ref name="pigliucci2003"/><ref>{{cite journal |last=Hull |first=D.L. |date=September 1978 |title=A matter of individuality |journal=[[Philosophy of Science (journal)|Philosophy of Science]] |volume=45 |issue=3 |pages=335–360 |doi=10.1086/288811 |s2cid=170157356 |url=http://www.phylosophy.org/Hull-Individuality-PoS1978.pdf }}</ref><ref>{{cite journal |last=Jardine |first=N. |date=March 1969 |title=A logical basis for biological classification |journal=Systematic Zoology |volume=18 |issue=1 |pages=37–52 |doi=10.2307/2412409 |jstor=2412409}}</ref>
-[[Jody Hey]] described the species problem as a result of two conflicting motivations by biologists:<ref name="heyGCS2001"/><ref name="hey2001"/>
-# to categorize and identify organisms;
-# to understand the evolutionary processes that give rise to species.
-Under the first view, species appear to us as typical natural kinds, but when biologists turn to understand species evolutionarily they are revealed as changeable and without sharp boundaries. [[Jody Hey|Hey]] argued that it is unrealistic to expect that one definition of "species" is going to serve the need for categorization and still reflect the changeable realities of evolving species.
-=== Pluralism and monism ===
-Many approaches to the species problem have attempted to develop one single common conception of what species are and of how they should be identified. It is thought that, if such a [[monism|monistic]] description of species could be developed and agreed upon, then the species problem would be solved. In contrast, some authors have argued for [[Scientific pluralism|pluralism]], claiming that biologists cannot have just one shared concept of species, and that they should accept multiple, seemingly incompatible ideas about species.<ref>{{cite book |last=Dupré |first=J. |year=1999 |chapter=On the impossibility of a monistic account of species |pages=[https://archive.org/details/speciesnewinterd00wils/page/n14 3]–22 |editor-last=Wilson |editor-first=R.A. |title=Species: New Interdisciplinary Essays |url=https://archive.org/details/speciesnewinterd00wils |url-access=limited |publisher=MIT Press |location=Cambridge, MA |isbn=978-0-262-73123-2}}</ref><ref>{{cite journal |last1=Mishler |first1=B.D. |last2=Donoghue |first2=M.J. |date=December 1982 |title=Species concepts: A case for pluralism |journal=Systematic Zoology |volume=31 |issue=4 |pages=491–503 |doi=10.2307/2413371 |jstor=2413371}}</ref><ref>{{cite journal |last=Ereshefsky |first=M. |date=December 1992 |title=Eliminative pluralism |journal=[[Philosophy of Science (journal)|Philosophy of Science]] |volume=59 |issue=4 |pages=671–690 |doi=10.1086/289701 |s2cid=224829314 }}</ref><ref>{{cite web |last1=Pigliucci |first1=Massimo |author1-link=Massimo Pigliucci |title=Wittgenstein Solves (Posthumously) the Species Problem|url=https://philosophynow.org/issues/50/Wittgenstein_Solves_Posthumously_the_Species_Problem |publisher=Philosophy Now |access-date=2 December 2016 |date=2005}}</ref> [[David Hull]] however argued that pluralist proposals were unlikely to actually solve the species problem.<ref name="Hull-Species" />
-== Quotations ==
-{{Copy section to Wikiquote}}
-"No term is more difficult to define than "species," and on no point are zoologists more divided than as to what should be understood by this word." Nicholson (1872).<ref name="nicholson1872">{{cite book |last=Nicholson |first=H.A. |year=1872 |title=A manual of zoology |publisher=Appleton and Company |location=New York |page=20}}</ref>
-"Of late, the futility of attempts to find a universally valid criterion for distinguishing species has come to be fairly generally, if reluctantly, recognized" Dobzhansky (1937).<ref name="dobzhansky1937">{{cite book |last=Dobzhansky |first=T. |author-link=Theodosius Dobzhansky |year=1937 |title=Genetics and the Origin of Species |publisher=Columbia University Press |location=New York |isbn=978-0-231-05475-1 |page=310|title-link=Genetics and the Origin of Species }}</ref>
-"The concept of a species is a concession to our linguistic habits and neurological mechanisms" Haldane (1956).<ref name="haldane1956">{{cite book |last=Haldane |first=J.B.S. |author-link=J. B. S. Haldane |year=1956 |chapter=Can a species concept be justified? |pages=95–96 |editor-last=Sylvester-Bradley |editor-first=P.C. |title=The species concept in paleontology |publisher=Systematics Association |location=London}}</ref>
-"An important aspect of any species definition whether in [[neontology]] or [[palaeontology]] is that any statement that particular individuals (or fragmentary specimens) belong to a certain species is an hypothesis (not a fact)" Bonde (1977).<ref>{{cite book |last=Bonde |first=N. |year=1977 |chapter=Cladistic classification as applied to vertebrates |title=Major Patterns in Vertebrate Evolution |editor1-last=Hecht |editor1-first=M.K. |editor2-last=Goody |editor2-first=P.C. |editor3-last=Hecht |editor3-first=B.M |pages=741–804 |publisher=Plenum Press |location=New York}}</ref>
-"The species problem is the long-standing failure of biologists to agree on how we should identify species and how we should define the word 'species'." Hey (2001).<ref name="hey2001">{{cite journal |last=Hey |first=J. |date=July 2001 |title=The mind of the species problem |journal=[[Trends in Ecology and Evolution]] |volume=16 |issue=7 |pages=326–329 |doi=10.1016/S0169-5347(01)02145-0 |pmid=11403864}}</ref>
-"First, the species problem is not primarily an empirical one, but it is rather fraught with philosophical questions that require — but cannot be settled by — empirical evidence." [[Pigliucci]] (2003).<ref name="pigliucci2003">{{cite journal |last=Pigliucci |first=Massimo |author-link=Massimo Pigliucci |date=June 2003 |title=Species as family resemblance concepts: The (dis-)solution of the species problem? |journal=[[BioEssays]] |volume=25 |issue=6 |pages=596–602 |doi=10.1002/bies.10284 |pmid=12766949|url=https://philpapers.org/rec/PIGSAF }}</ref>
-"We show that although discrete phenotypic clusters exist in most <nowiki>[plant]</nowiki> genera (> 80%), the correspondence of taxonomic species to these clusters is poor (< 60%) and no different between plants and animals. ... Contrary to conventional wisdom, plant species are more likely than animal species to represent reproductively independent lineages." Rieseberg et al. (2006).<ref>{{cite journal |author1=Rieseberg, L.H. |author2=Wood, T.E. |author3=Baack, E.J. |year=2006 |title=The nature of plant species |journal=Nature |volume=440 |issue=524–527 |pages=524–527 |doi=10.1038/nature04402|pmid=16554818 |bibcode=2006Natur.440..524R |pmc=2443815 }}</ref>
-== See also ==
-* [[Evolutionarily significant unit]] (ESU)
-* [[Ring species]]
-== References ==
-{{reflist|30em}}
-== External links ==
-{{Wikispecies|Species}}
-* [http://scienceblogs.com/evolvingthoughts/2006/10/01/a-list-of-26-species-concepts/ A catalogue of species conceptions]
-* [http://www.curioustaxonomy.net/ Curiosities of Biological Nomenclature]
-[[Category:Species]]
-[[Category:Unsolved problems in biology]]