CHAPTERSIXSpecies Are Not Uniquely RealBiological EntitiesBrent D. MishlerAre species uniquely real biological entities? This question is one of the most controver-sial topics today in such areas of biology as ecology, systematics, conservation, populationgenetics, and evolution. “Species” currently play a central role in both theory and practicein these areas, and have a large place in the public’s perception of biological diversityas well. This question can be decomposed into two parts: (1) Are species real, and inwhat sense? (2) If real, is their reality the same as entities smaller or larger than them—i.e., are they real in a sense that genera or subspecies are not? This paper will brieflyreview historical and current opinions on these questions, but will primarily advocateone particular position that appears to fit biological reality as now understood: that speciesproperly defined are real entities, but not uniquely real. The longstanding “species problem”can be solved by realizing that there is no such thing as species after all! The so-called“species problem” is really just a special case of the taxon problem. Once a decision ismade about what taxa in general are to represent, then those groups currently knownas species are simply the least inclusive taxa of that type. As I favor a phylogeneticbasis for taxonomy, I want to look at how to include terminal taxa in the PhyloCode,currently a controversial topic even among PhyloCode supporters. In brief, my argumentis: (1) life is organized in a hierarchy of nested monophyletic groups—some of themquite fine-scale, well below the level we currently call species; (2) not all known mono-phyletic groups need be named, just the ones that are important to process or conser-vation studies and that have good support; (3) those that are named taxonomically shouldbe given unranked (but hierarchically nested) uninomials; and (4) formal ranks, includ-ing species, should be abandoned. I will conclude with a brief discussion of the impli-cation of my position on species for academic studies in ecology and evolution as wellas for practical applications in biodiversity inventories and conservation biology.But be warned, you who thirst for knowledge, be warned about the thicket of opinions andthe fight over words.Hermann Hesse, SiddharthaCDI_C06.qxd 8/24/09 2:16 PM Page 110Contemporary Debates in Philosophy of Biology Edited by Francisco J. Ayala and Robert Arp© 2010 Blackwell Publishing Ltd. ISBN: 978-1-405-15998-21 Historical and Current Views of SpeciesOver the history of science, people have taken a number of different positions onthese issues involving the reality of species. The fundamental view throughout theclassical period (basically from the ancient Greeks until Darwin) was that species areindeed the basic, real units of life. The basis for their reality was initially conceivedof in a typological or idealistic framework; species were viewed as the basic kindsor types of living things. Later, under the influence of Christian theology, the basisfor the fundamental reality of species changed somewhat. They were still viewed asbasic kinds, but now as specially created “ideas” in the mind of the creator.Taxonomic groups at more inclusive levels were also manifestations of the creator’sideas, but species were the fundamental kinds, the building blocks of life. This ideacontinues to the present in the attitudes of the majority of the general public in theUnited States, under the influence of creationism.The course of science took a somewhat different path than the public view. TheDarwinian revolution did not question the reality of species in scientists’ thinking(although see below for Darwin’s contribution to a shift in thinking about their unique-ness), but changed the perception of their nature greatly. Instead of representing anatural kind defined by certain necessary and sufficient characteristics, species cameto be seen as a natural genealogical unit composed of organisms historically relatedto each other, with a beginning and an end, not defined by any characteristics (i.e.,“individuals” in the philosophical sense; Ghiselin, 1974; Hull, 1978; Mishler &Brandon, 1987). They were viewed as a cross-section of a lineage (de Quieroz, 1999).In the Modern Synthesis (called such at the time, but looking rather dated these days!),a view solidified of species being the largest group of interbreeding organisms (thegene pool) and as such the most fundamental unit in which evolutionary changetakes place (the biological species concept; BSC; Mayr, 1942, 1982). Species came tobe regarded as a fundamental level in the hierarchy of biological organization (e.g.,molecule, cell, tissue, organism, population, species, community, ecosystem).This view was nearly unanimous until the 1960s, when, under the influence ofhighly empirical operationalist philosophies of science then in style, and the seemingly “objective” application of computer algorithms to science, an approachemerged called “numerical taxonomy” or “phenetics.” In this view, taxa at all levels, including species, were viewed in a nominalistic manner. A species was justa cluster of similar organisms grouped at some arbitrary numerical level of similarity(the phenetic species concept; Levin, 1979; Sokal & Crovello, 1970). It was consideredto be unnecessary and wrong-headed to require anything about a deeper basis forreality, whether relatedness or interbreeding ability, to describe species. If named specieslater turned out to be something useful for inferences about evolutionary or ecologicalprocesses, then fine, but their recognition as species was best kept separate from pro-cess considerations.One trend apparent in the history of thinking about species has to do with organ-ismal specialty; to a large extent, there has been a sociological difference amongcommunities of systematists studying different kinds of organisms. Zoologists tendedto favor the biological species concept (Coyne, Orr, & Futuyma, 1988), whilebotanists and bacteriologists tended to favor the phenetic species concept (e.g., Levin,1979; Sokal & Crovello, 1970). There have been some exceptions: for example, GrantSpecies Are Not Uniquely Real Biological Entities 111CDI_C06.qxd 8/24/09 2:16 PM Page 111(1981), Rieseberg and Burke (2001), and Stebbins (1950) represent a minority BSCtradition viewpoint among botanists, while Wheeler (1999) represents a minority non-BSC
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