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On The Changing Definition of the Term "Species"
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Kenneth B. Cumming, Ph.D.
IMPACT
No. 211, January 1991
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Nelson [1] has written, "The 'species problem' is perennial (Howard, 1988),and speciation remains as much a black box as ever (Jackson, 1988). If weexamine these problems we find a spectrum of solutions: some writers claimthat everything, or everything important, is known; others claim thatnothing, or nothing important, is known (Hull, 1988). I claim that theproblems are insoluble, for they stem from a false assumption: that there isan empirical difference between species and the taxa such that speciesevolve through speciation of other species.... Evolution of taxa is not aphenomenon confined to the species level except in neo-Darwinian theory,which in this respect is simply false."
One would think that surely by now scientists would have agreed on thedefinition of this fundamental term in systematics—species. In truth, whilemost biologists would quickly offer their preferred definition when asked,each could also be unsettled by challenging their response with an alternateinterpretation. What is the underlying problem in this uncertainty? Ibelieve it lies in the presuppositions of the various writers. In this first of a series of Impact articles, the term "species" will beexamined to demonstrate the wide diversity of definitions. No attempt willbe made to give detailed explanations of the concepts involved in thefollowing definitions at this time. In forthcoming articles the terms of"speciation" and "specialization" will be reviewed. It is expected that acomparison of evolution and creation thinking on these terms will lead to asharp separation of perspective on the "species problem."
| Species Concepts
Let us start with Aristotle and work our way forward to a creationist, tospeculate on the rationale for the various definitions. Goerke [2] states,"The earliest scientific classification of objects in nature was made byAristotle in the fourth century B.C., and the principles he establishedretained their authority well into the sixteenth century and even into theseventeenth." He divided plants into trees, bushes, and herbs, and animalsinto those with and those without circulatory systems (very generallyvertebrates and invertebrates). Mayr [3] adds, " Typologicalthinking...according to this concept the vast observed variability of theworld has no more reality than the shadows of an object on a cave wall, asPlato puts it in his allegory. Fixed, unchangeable 'ideas' underlying theobserved variability are the only things that are permanent and real.... Theconcepts of unchanging essences and of complete discontinuities betweenevery eidos (type) and all others make genuine evolutionary thinkingwell-nigh impossible."
| "Linnaeus did a great service to taxonomy when he invented a definiteterminology for the systematic categories and showed that they could bearranged in a graded hierarchy: species, genus, family, order, and class...he adhered always to an essentially static and morphological speciesconcept." [4] Thus, Linnaeus, about 1735, believed that species was a termfor an objective and highly separate group of organisms; as a creationist hewanted to delineate the Genesis "kinds" in his systematics. Members of thegroup did vary, but by and large, the history of the group (lineage) showeda consistency of traits since the type was formed.
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Darwin's [5] interpretation of species in 1859 was simply practical: "I lookat the term species as one arbitrarily given for the sake of convenience toa set of individuals closely resembling each other...it does not essentiallydiffer from the term variety which is given to less distinct and morefluctuating forms." To him a species was any group of organisms thatcompetent naturalists said was a species. All organisms were seen as part ofa continuum from some single primeval entity.The next major different concept in the term species was introduced around1940 by Dobzhansky and Mayr: It was the biological species concept. For along time this thinking has saturated much of the evolutionary literature.Mayr [6] presents his definition: "A biological species definition, based onthe criteria of crossability or reproductive isolation, has theoreticallyfewer flaws than any other...Species are groups of actually or potentiallyinterbreeding natural populations, which are reproductively isolated fromother such groups." Obviously, this is a much more concrete interpretationof species for evolutionary considerations than Darwin's, and more dynamicthan that of Linnaeus. However, this concept does not lend itself tounderstanding the process of speciation. Thus, Templeton [7] reviewed the problems associated with various"biological species concepts" and introduced his cohesion concept, "thatdefines a species as the most inclusive group of organisms having thepotential for genetic and/or demographic exchangeability. This conceptborrows from all three biological species concepts. Unlike the isolation andrecognition concepts, it is applicable to the entire continuum ofreproductive systems observed in the organic world. Unlike the evolutionaryconcept, it identifies specific mechanisms that drive the evolutionaryprocess of speciation." There are other concepts [8], [9] that have been putforward that could be developed, but let's go on to a different line ofthought from the three phylogenetic examples used above. Hennig, [10] as a (cladist), views biological diversity with a different goalin mind than the phylogeneticist. "...in a hierarchical system, eachgroup formation relates to a 'beginner' which is linked in 'one-manyrelations' with all of the members of that group and only those. Inmorphological systems, the 'beginner' which belongs to each group is aformal idealistic standard (Archetype) whose connections with the othermembers of the group are likewise purely formal and idealistic. But, in thephylogenetic system, the 'beginner' to which each group formation relates isa real reproductive community which has at some time in the past reallyexisted as the ancestral species of the group in question, independently ofthe mind which conceives it, and which is linked by genealogical connectionswith the other members of the group and only with these." The cladistdefinition of species is similar to that of Mayr, above—the reproductivecommunities that occur in nature. However, due to the unique methodology ofmorphological resemblance systematics, different principles ofclassification are employed above and below the specific level. Cladism isessentially typological. As a final example, I would now like to review a creationist concept ofspecies. ReMine [11] has recently put forward an alternate systematicmethodology to the prevalent phylogenetic systems. He calls it"discontinuity systematics." In the scheme, he explains that "species" wasmerely the Latin word for "kind." For various reasons, he coins termsrelated to the synthetic Hebrew word "baramin" to apply to workingdefinitions of this innovative system. Frank Marsh [12] originally combinedthe Hebrew root words bara ("create") and min ("kind") into the term" baramin." Although there is no direct statement to this effect, the term "holobaramin," or its subset " monobaramin," might include or in someinstances be synonymous with species. Yet the emphasis is uponexperimentally circumscribing the continuities and locating the real gaps ordiscontinuities in nature. Empirical research on delineating holobaramins isjust starting.
| Summary
With tongue in cheek, I originally entitled this article, "On the Origin of'Species'," to play on the history of the term species as a concept. Most ofthe systematic literature would certainly deal with phylogenetic definitionsof the taxonomic class—species. Nevertheless, there are some uses, both oldand new, that refer to species typologically. Granted, most typologicalcladists would never associate with a creationist perspective, for they arethorough-going evolutionists, even if they do not agree with Darwinian oreven neo-Darwinian extrapolations. The following table might represent apartial summary of representative methods involving the species concert.
| | Concept's Author | Systematic Methodology | Species Taxon Synonym | | Aristotle | typology | essences | | Linnaeus | typology | kinds | | Darwin | phylogeny | variants | | Mayr | phylogeny | isolates | | Templeton | phylogeny | exchangeables | | Hennig | typology | clades | | ReMine | typology | holobaramins |
| Biosystematic uses of the term 'species' mentioned in this article, exceptpossibly in cladistics, appear to imply real reproductive communities oforganisms, when they deal with non-fossil species. It can be seen that thedefinition of species, which started out essentially as a morphologicalterm, has taken on a functional or operational meaning. Underlying thisdynamic component are presuppositions related to variance—limited orunlimited. In the next article of this particular series, the evidence forspeciation be discussed.
| References
[1] G. Nelson, Species and Taxa: Systematics and Evolution, in D. Otte and J.A. Endler, Speciation and its Consequences (Sunderland, Massachusetts, Sinauer, 1989) pp. 73,74. Return to Text
[2] H. Goerke, Linnaeus (New York, Charles Scribner's Sons, 1973), p. 90. Return to Text
[3] E. Mayr, Animal Species and Evolution (Cambridge, Massachusetts, The Belknap Press of Harvard University Press, 1979), p. 9. Return to Text
[4] E. Mayr, Systematics and the Origin of Species (New York, Columbia University Press, 1944), p. 102. Return to Text
[5] C. Darwin, The Origin of Species by Means of Natural Selection, or the Preservation of Favored Races in the Struggle for Life (New York, Avenel Books, 1970), p. 108. Return to Text
[6] E. Mayr, 1944, op cit., p. 120. Return to Text
[7] A.R. Templeton, The Meaning of Species and Speciation: A Genetic Perspective, in D. Otte and J.A. Endler, Speciation and its Consequences (Sunderland, Massachusetts, Sinauer, 1989), p. 25. Return to Text
[8] J. Cracraff, Speciation and its Ontology. The Empirical Consequences of Alternative Species Concepts for Understanding Patterns and Processes of Differentiation, in D. Otte and J.A. Endler, Speciation and its Consequences (Sunderland, Massachusetts, Sinauer, 1989), pp. 28-59. Return to Text
[9] A.G. Kluge, "Species as Historical Individuals," Biology and Philosophy 5 (1990): 417-431. Return to Text
[10] W. Hennig, Phylogenetic Systematics, in T. Duncan and T.F. Stuessy, Cladistic Theory and Methodology (New York, Van Nostrand Reinhold Company, 1985), p. 14. Return to Text
[11] W.J. ReMine, "Discontinuity Systematics: A New Methodology of Biosystematics Relevant to the Creation Model," Ms. presented at The Second International Conference on Creationism, 1990, held at Pittsburgh, Pennsylvania on July 29-August 4, 1990. Return to Text
[12] F.L. March, Fundamental Biology (Lincoln, Nebraska, Marsh Publication, 1941), p. 100. Return to Text
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"Vital Articles on Science/Creation"
January 1991
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