Abstract
A natural starting place for developing a phylogenetic species concept is to examine monophyletic groups of organisms. Proponents of “the” Phylogenetic Species Concept fall into one of two camps. The first camp denies that species even could be monophyletic and groups organisms using character traits. The second groups organisms using common ancestry and requires that species must be monophyletic. I argue that neither view is entirely correct. While monophyletic groups of organisms exist, they should not be equated with species. Instead, species must meet the more restrictive criterion of being genealogically exclusive groups where the members are more closely related to each other than to anything outside the group. I carefully spell out different versions of what this might mean and arrive at a working definition of exclusivity that forms groups that can function within phylogenetic theory. I conclude by arguing that while a phylogenetic species concept must use exclusivity as a grouping criterion, a variety of ranking criteria are consistent with the requirement that species can be placed on phylogenetic trees.
Similar content being viewed by others
Notes
By a ‘diverging’ phylogeny I mean that branches split but never join. Equivalently, each node (other than the root) has precisely one parent. It is tempting to think that a diverging phylogeny means that the horizontal distance between tips represents phenotypic divergence as well but this is not correct. For example, instances of convergent evolution take place on a diverging tree.
Baum and Shaw (1995) anticipate much of the above discussion and conclude that taxa should be exclusive groups, but deny that exclusivity can be understood in MRCA terms. They do this because they wish to define species as basal taxa and some exclusive groups would be too small to be species. However, here, I do not assume that species are the smallest exclusive groups; rather, I am searching for a general phylogenetic grouping criterion and a general understanding of exclusive groups of organisms.
References
Baum DA (1992) Phylogenetic species concepts. Trends Ecol Evol 7(1):1–2. doi:10.1016/0169-5347(92)90187-G
Baum DA (1998) Individuality and the existence of species through time. Syst Biol 47(4):641–653. doi:10.1080/106351598260644
Baum DA (2009) Species as ranked exclusive groups. Syst Biol (forthcoming)
Baum DA, Donoghue MJ (1995) Choosing among alternative “phylogenetic” species concepts. Syst Bot 20(4):560–573. doi:10.2307/2419810
Baum DA, Shaw KL (1995) Genealogical perspectives on the species problem. In: Hoch PC, Stephenson AG (eds) Experimental and molecular approaches to plant biosystematics. Missouri Botanical Garden, St. Louis, pp 289–303
Chang JT (1999) Recent common ancestors of all present-day individuals. Adv Appl Probab 31:1002–1026. doi:10.1239/aap/1029955256
Cracraft J (1983) Species concepts and speciation analysis. Curr Ornithol 1:159–187
Dawkins R (2004) The Ancestor’s tale. Houghton Mifflin Company, New York
de Queiroz K, Donoghue M (1988) Phylogenetic systematics and the species problem. Cladistics 4:317–338. doi:10.1111/j.1096-0031.1988.tb00518.x
de Queiroz K, Donoghue M (1990) Phylogenetic systematics or Nelson’s version of cladistics? Cladistics 6:61–75. doi:10.1111/j.1096-0031.1990.tb00525.x
Donoghue MJ (1985) A critique of the biological species concept and recommendations for a phylogenetic alternative. Bryologist 88(3):172–181. doi:10.2307/3243026
Dupré J (1993) The disorder of things: metaphysical foundations of the disunity of science. Harvard University Press, Cambridge
Eldredge N, Cracraft J (1980) Phylogenetic patterns and the evolutionary process: method and theory in comparative biology. Columbia University Press, New York
Ereshefsky M (1992) Eliminative pluralism. Philos Sci 59:671–690. doi:10.1086/289701
Hennig W (1966) Phylogenetic systematics. University of Chicago Press, Chicago
Kitcher P (1984) Species. Philos Sci 51:308–333. doi:10.1086/289182
LaPorte J (2005) Is there a single objective, evolutionary tree of life? J Philos 102(7):357–374
McNeill J, Barrie FR, Burdet HM, Demoulin V, Hawksworth DL, Marhold K, Nicolson DH, Prado J, Silva PC, Skog JE, Wiersema JH, Turland NJ (eds) (2006) International code of botanical nomenclature (Vienna Code) adopted by the seventeenth international botanical congress Vienna, Austria, July 2005. Gantner Verlag, Ruggell
Meier R, Willman R (2000) The Hennigian species concept. In: Wheeler QD, Platnick N (eds) Species concepts and phylogenetic theory. Columbia University Press, New York, pp 44–54
Mishler BD (1985) The morphological, developmental, and phylogenetic basis of species concepts in bryophytes. Bryologist 88(3):207–214. doi:10.2307/3243030
Mishler BD, Brandon RN (1987) Individuality, pluralism, and the phylogenetic species concept. Biol Philos 2:397–414. doi:10.1007/BF00127698
Mishler BD, Donoghue MJ (1982) Species concepts: a case for pluralism. Syst Zool 31(4):491–503. doi:10.2307/2413371
Mishler BD, Theriot EC (2000) The phylogenetic species concept (Sensu Mishler and Theriot). In: Wheeler QD, Platnick N (eds) Species concepts and phylogenetic theory. Columbia University Press, New York, pp 44–54
Nelson G (1979) Cladistic analysis and synthesis: principles and definitions, with a historical note on Adanson’s Familles des Plantes (1763–1764). Syst Zool 28:1–21. doi:10.2307/2412995
Nixon K, Wheeler Q (1990) An amplification of the phylogenetic species concept. Cladistics 6(3):211–223. doi:10.1111/j.1096-0031.1990.tb00541.x
Pleijel F, Rouse GW (2000) Least-inclusive taxonomic unit: a new taxonomic concept for biology. Proc R Soc Lond B Biol Sci 267:627–630. doi:10.1098/rspb.2000.1048
Rohde DLT (manuscript) On the common ancestors of all living humans. Available online at: http://tedlab.mit.edu/~dr/
Rohde DLT, Olson S, Chang JT (2004) Modelling the recent common ancestry of all living humans. Nature 431(7008):562–566. doi:10.1038/nature02842
Rosen DE (1978) Vicariant patterns and historical explanation in biogeography. Syst Zool 27(2):159–188. doi:10.2307/2412970
Sober E (2000) The philosophy of biology (2nd edition). Westview, Boulder, CO
Stanford K (1995) For pluralism and against realism about species. Philos Sci 62:70–91. doi:10.1086/289840
Velasco JD (2008) Species concepts should not conflict with evolutionary history, but often do. Stud Hist Philos Biol Biomed Sci 39:407–414. doi:10.1016/j.shpsc.2008.09.007
Wheeler QD, Platnick N (2000) The phylogenetic species concept (Sensu Wheeler and Platnick). In: Wheeler QD, Platnick N (eds) Species concepts and phylogenetic theory. Columbia University Press, New York, pp 55–69
Wiley E (1981) Phylogenetics: the theory and practice of phylogenetic systematics. Wiley-Interscience, New York
Acknowledgments
Thanks to Matt Barker, David Baum, Marc Ereshefsky, Casey Helgeson, Brent Mishler, Greg Novack, Elliott Sober, Kim Sterelny, and John Wilkins, all of whom provided helpful comments on earlier drafts of this paper.
Author information
Authors and Affiliations
Corresponding author
Rights and permissions
About this article
Cite this article
Velasco, J.D. When monophyly is not enough: exclusivity as the key to defining a phylogenetic species concept. Biol Philos 24, 473–486 (2009). https://doi.org/10.1007/s10539-009-9151-4
Received:
Accepted:
Published:
Issue Date:
DOI: https://doi.org/10.1007/s10539-009-9151-4