Skip to main content
Log in

Is convergence more than an analogy? Homoplasy and its implications for macroevolutionary predictability

  • Original Paper
  • Published:
Biology & Philosophy Aims and scope Submit manuscript


A number of authors have pointed to “convergent evolution” as evidence for the central role of natural selection in shaping predictable trajectories of macroevolution. However, there are numerous conceptual and empirical difficulties that arise in broadly appealing to the frequency of homoplasy as evidence for a non-contingently constrained adaptational design space. Most important is the need to distinguish between convergent (externally constrained) and parallel (internally constrained) evolution, and to consider how the respective frequencies of these significantly different sources of homoplasy affect a strong adaptationist view of life. In this paper, I critically evaluate Simon Conway Morris’s use of the homoplasy literature to support his argument for a non-contingent, counterfactually stable account of macroevolutionary pattern. In so doing, I offer a conception of parallelism which avoids the charge that it differs from convergence merely in degree and not in kind. I argue that although organisms sharing a homoplastic trait will also share varying degrees of homology, it is the underlying developmental homology with respect to the generators directly causally responsible for the homoplastic event that defines parallel evolution and non-arbitrarily distinguishes it from convergence. The notion of “screening-off” is used to distinguish the proximal generators of a homoplastic trait from its more distal genetic causes (such as a master control gene).

This is a preview of subscription content, log in via an institution to check access.

Access this article

Subscribe and save

Springer+ Basic
EUR 32.99 /Month
  • Get 10 units per month
  • Download Article/Chapter or Ebook
  • 1 Unit = 1 Article or 1 Chapter
  • Cancel anytime
Subscribe now

Buy Now

Price excludes VAT (USA)
Tax calculation will be finalised during checkout.

Instant access to the full article PDF.

Fig. 1

Similar content being viewed by others


  1. See, e.g., Conway Morris (2003); Foley (1999); Dennett (1995).

  2. Gene regulatory networks are hierarchical, with earlier linkages having more pleiotropic effects than the more distal fine-grained terminal processes. The former upstream sub-circuits, which Davidson and Erwin (2006) have termed “kernels,” specify the more general domain of the developing organism. Because kernels are “recursively” wired, interference with any single kernel gene will destroy its function altogether, resulting in phenotypic catastrophe.

  3. Haas preferred to distinguish convergence and parallelism geometrically (rather than causally)—with the former entailing that two lineages resemble one another more than their ancestors did, and the latter referring to cases in which two lineages evolve in the same direction without resembling one another any more than their ancestors did. For example, a trend of increasing body size in grasshopper and walrus clades would represent a parallelism for Haas, although Simpson would presumably demur since the parallel increases are probably not linked to shared developmental homology.

  4. The misexpression of the Pax-6 transcription factor has been shown to lead to the formation of differentiated ectopic eyes in both vertebrates and invertebrates. This data may seem to represent a counterexample to the claim that Pax-6 is casually insufficient for the formation of the macroscopic eye. However, this objection is neutralized by the contingent fact that the abnormal expression of Pax-6 simply triggers a cascade of downstream developmental events which are directly responsible for the substance and structure of the ectopic eye.

  5. SCM does draw upon some examples of genuine convergence that could be the subject of robust macrobiological generalizations, such as those pertaining to sensory modalities (2003, Ch. 7); unfortunately, he offers no principled method for comparing the philosophical or inductive significance of different types of homoplasy. Additionally, he fails to show that any of the evolutionary endpoints that he infers from the distribution of homoplasy are associated with either diversification or persistence (or some other measure of evolutionary success), which (in my view) undercuts the notion that such outcomes represent stable islands of form amidst a roiling sea of stochasticity.

  6. I would like to thank Robert Brandon, Dan McShea, Alex Rosenberg, members of the Duke Philosophy of Biology Reading Group, and (especially) an anonymous referee for helpful comments on an earlier draft of this paper. Thanks also to Victoria Campbell for kindly sketching the illustrations in Fig. 1. Finally, I am indebted to the late Stephen Jay Gould, whose popular works encouraged me to explore philosophical issues in the history of life.


  • Amundson R (1994) Two concepts of constraint: adaptationism and the challenge from developmental biology. Philos Sci 61:556–578

    Google Scholar 

  • Beatty J (1995) The evolutionary contingency thesis. In: Wolters G, Lennox J (eds) Concepts, theories, and rationality in the biological sciences. University of Pittsburgh Press, Pennsylvania

    Google Scholar 

  • Brandon RN (1990) Adaptation and environment. Princeton University Press, Princeton

    Google Scholar 

  • Carroll SB (2005) Endless forms most beautiful: the new science of evo devo. W.W. Norton, New York

    Google Scholar 

  • Conway Morris S (1998) The crucible of creation: the burgess shale and the rise of animals. Oxford University Press, Oxford

    Google Scholar 

  • Conway Morris S (2003) Life’s solution: inevitable humans in a lonely universe. Cambridge University Press, Cambridge

    Google Scholar 

  • Davidson EH, Erwin DH (2006) Gene regulatory networks and the evolution of animal body plans. Science 311:796–800

    Article  Google Scholar 

  • Dennett DC (1995) Darwin’s dangerous idea. Simon & Schuster, New York

    Google Scholar 

  • Diogo R (2005) Evolutionary convergences and parallelisms: their theoretical differences and the difficulty of discriminating them in a practical context. Biol Philos 20:735–744

    Article  Google Scholar 

  • Foley R (1999) Pattern and process in hominid evolution. In: Bintliff J (ed) Structure and contingency: evolutionary processes in life and human society. Leicester University Press, London

    Google Scholar 

  • Gehring WJ, Ikeo K (1999) Pax 6: mastering eye morphogenesis and eye evolution. Trends Genet 15(9):371–377

    Article  Google Scholar 

  • Gould SJ (1989) Wonderful life: the burgess shale and the nature of history. W.W. Norton, New York

    Google Scholar 

  • Gould SJ (2002) The structure of evolutionary theory. Harvard University Press, Cambridge

    Google Scholar 

  • Haas O, Simpson GG (1946) Analysis of some phylogenetic terms with attempts at redefinition. Proc Am Philos Soc 90:319–349

    Google Scholar 

  • Harris MP, Hasso SM, Ferguson MWJ, Fallon JF (2006) The development of archosaurian first-generation teeth in a mutant chicken. Curr Biol 16:371–377

    Article  Google Scholar 

  • Hunter J, Jernvall JP (1995) The hypocone as a key innovation in mammalian evolution. Proc Natl Acad Sci USA 92:10718–10722

    Article  Google Scholar 

  • Land MF, Fernald RD (1992) The evolution of eyes. Annu Rev Neurosci 15:1–29

    Article  Google Scholar 

  • Patterson C (1988) Homology in classical and molecular biology. Mol Biol Evol 5:603–625

    Google Scholar 

  • Rosenberg A (2001) How is biological explanation possible? Br J Philos Sci 52(4):735–760

    Article  Google Scholar 

  • Salmon WC (1971) Statistical explanation and statistical relevance. University of Pittsburgh Press, Pittsburgh

    Google Scholar 

  • Shapiro MD, Marks ME, Peichel CL, Blackman BK, Nereng KS, Jónsson B, Schluter D, Kingsley DM (2004) Genetic and developmental basis of evolutionary pelvic reduction in three spine sticklebacks. Nature 428:717–723

    Article  Google Scholar 

  • Simpson GG (1961) Principles of animal taxonomy. Columbia University Press, New York

    Google Scholar 

  • Sterelny K (1996) Explanatory pluralism in evolutionary biology. Biol Philos 11:193–214

    Article  Google Scholar 

  • Sterelny K (2005) Another view of life. Stud Hist Philos Biol Biomed Sci 36:585–593

    Article  Google Scholar 

  • Van Valen L (1973) A new evolutionary law. Evol Theory 1:1–30

    Google Scholar 

  • Vermeij GJ (1994) Evolutionary interaction among species: selection, escalation, and coevolution. Annu Rev Ecol Syst 25:219–236

    Article  Google Scholar 

  • Vogel S (1996) Diversity and convergence in the study of organismal function. Isr J Zool 42:297–305

    Google Scholar 

  • Vogel S (1998) Convergence as an analytical tool in evaluating design. In: Weibel ER, Taylor CR, Bolis L (eds) The optimization and symmorphosis debate. Cambridge University Press, Cambridge

    Google Scholar 

  • Wake DB (1991) Homoplasy: the result of natural selection or evidence of design limitation? Am Nat 138:543–567

    Article  Google Scholar 

  • Zuker CS (1994) On the evolution of eyes: would you like it simple or compound ? Science 265:742–743

    Article  Google Scholar 

Download references

Author information

Authors and Affiliations


Corresponding author

Correspondence to Russell Powell.

Rights and permissions

Reprints and permissions

About this article

Cite this article

Powell, R. Is convergence more than an analogy? Homoplasy and its implications for macroevolutionary predictability. Biol Philos 22, 565–578 (2007).

Download citation

  • Received:

  • Accepted:

  • Published:

  • Issue Date:

  • DOI: