Biology & Philosophy

, Volume 24, Issue 4, pp 473–486 | Cite as

When monophyly is not enough: exclusivity as the key to defining a phylogenetic species concept

  • Joel D. Velasco


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.


Genealogical exclusivity Monophyly Phylogenetic species concept Phylogenetic systematics Species 



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.


  1. Baum DA (1992) Phylogenetic species concepts. Trends Ecol Evol 7(1):1–2. doi: 10.1016/0169-5347(92)90187-G CrossRefGoogle Scholar
  2. Baum DA (1998) Individuality and the existence of species through time. Syst Biol 47(4):641–653. doi: 10.1080/106351598260644 CrossRefGoogle Scholar
  3. Baum DA (2009) Species as ranked exclusive groups. Syst Biol (forthcoming)Google Scholar
  4. Baum DA, Donoghue MJ (1995) Choosing among alternative “phylogenetic” species concepts. Syst Bot 20(4):560–573. doi: 10.2307/2419810 CrossRefGoogle Scholar
  5. 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 289–303Google Scholar
  6. Chang JT (1999) Recent common ancestors of all present-day individuals. Adv Appl Probab 31:1002–1026. doi: 10.1239/aap/1029955256 CrossRefGoogle Scholar
  7. Cracraft J (1983) Species concepts and speciation analysis. Curr Ornithol 1:159–187Google Scholar
  8. Dawkins R (2004) The Ancestor’s tale. Houghton Mifflin Company, New YorkGoogle Scholar
  9. 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 CrossRefGoogle Scholar
  10. 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 CrossRefGoogle Scholar
  11. 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 CrossRefGoogle Scholar
  12. Dupré J (1993) The disorder of things: metaphysical foundations of the disunity of science. Harvard University Press, CambridgeGoogle Scholar
  13. Eldredge N, Cracraft J (1980) Phylogenetic patterns and the evolutionary process: method and theory in comparative biology. Columbia University Press, New YorkGoogle Scholar
  14. Ereshefsky M (1992) Eliminative pluralism. Philos Sci 59:671–690. doi: 10.1086/289701 CrossRefGoogle Scholar
  15. Hennig W (1966) Phylogenetic systematics. University of Chicago Press, ChicagoGoogle Scholar
  16. Kitcher P (1984) Species. Philos Sci 51:308–333. doi: 10.1086/289182 CrossRefGoogle Scholar
  17. LaPorte J (2005) Is there a single objective, evolutionary tree of life? J Philos 102(7):357–374Google Scholar
  18. 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, RuggellGoogle Scholar
  19. 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 44–54Google Scholar
  20. Mishler BD (1985) The morphological, developmental, and phylogenetic basis of species concepts in bryophytes. Bryologist 88(3):207–214. doi: 10.2307/3243030 CrossRefGoogle Scholar
  21. Mishler BD, Brandon RN (1987) Individuality, pluralism, and the phylogenetic species concept. Biol Philos 2:397–414. doi: 10.1007/BF00127698 CrossRefGoogle Scholar
  22. Mishler BD, Donoghue MJ (1982) Species concepts: a case for pluralism. Syst Zool 31(4):491–503. doi: 10.2307/2413371 CrossRefGoogle Scholar
  23. 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 44–54Google Scholar
  24. 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 CrossRefGoogle Scholar
  25. 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 CrossRefGoogle Scholar
  26. 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 CrossRefGoogle Scholar
  27. Rohde DLT (manuscript) On the common ancestors of all living humans. Available online at:
  28. 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 CrossRefGoogle Scholar
  29. Rosen DE (1978) Vicariant patterns and historical explanation in biogeography. Syst Zool 27(2):159–188. doi: 10.2307/2412970 CrossRefGoogle Scholar
  30. Sober E (2000) The philosophy of biology (2nd edition). Westview, Boulder, COGoogle Scholar
  31. Stanford K (1995) For pluralism and against realism about species. Philos Sci 62:70–91. doi: 10.1086/289840 CrossRefGoogle Scholar
  32. 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 CrossRefGoogle Scholar
  33. 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 55–69Google Scholar
  34. Wiley E (1981) Phylogenetics: the theory and practice of phylogenetic systematics. Wiley-Interscience, New YorkGoogle Scholar

Copyright information

© Springer Science+Business Media B.V. 2009

Authors and Affiliations

  1. 1.Stanford UniversityStanfordUSA

Personalised recommendations