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parallelismparallelisme (fr.); Parallelismus (ger.)

  • 1) Originally: between the morphology or developmental stages of related organisms, esp. as explained in terms of recapitulation theory (obs.). (OED 2012)

    parallelism in the forms of life

    Darwin, C. (1859). On the Origin of Species: 325.

  • 2) In later use: the development of similar characteristics by two related groups of organisms, in response to similar environmental pressures; parallel evolution. (OED 2012)

    The relation of genera, which are simply steps in one and the same line of development, may be called exact parallelism, while that of those where one or more characters intervene in the maturity of either the lower or higher genus to destroy identity, may be called incomplete parallelism.

    Cope, E.D. (1868). On the origin of genera. Proceedings of the Academy of Natural Sciences of Philadelphia 20, 242-300: 295.


    Among the higher groups [of Lacertilia Leptoglossa] the parallelisms lie in the arrangement […] of the head shields.

    Cope, E.D. (1887). Origin of the Fittest: 98; 102.


    if the various species of the ancestral genus may acquire the new character independently of each other (parallelism), or if the species of widely different genera may gradually assume a common likeness (convergence), then it is plain that such a genus is an artificial assemblage of forms of polyphyletic origin.

    Scott, W.B. (1891). On the osteology of Mesohippus and Leptomeryx, with observations on the modes and factors of evolution in the Mammalia. Journal of Morphology 5, 301-402: 362.

    similar characters arising independently in similar or related animals or organs, causing a similar evolution, and resulting in parallelisms
    Osborn, H.F. (1905). The ideas and terms of modern philosophical anatomy. Science 21, 959-961: 960.

    a high degree of taxonomic distance between the initial members of the converging lineages is, in our opinion, not essential for convergence, we have decided to support strictly geometric definitions, viz. of parallelism as homoplastic modifications in two or more lines producing similarities which do not increase with evolution, and of convergence as such modifications producing similarities which do increase with evolution.

    Haas, O. & Simpson, G.G. (1946). Analysis of some phylogenetic terms, with attempts at redefinition. Proceedings of the American Philosophical Society 90, 319-349: 338.


    parallelism would be similarity in structure due to common genetic basis (and so far resembling homology) but not reaching morphological expression until after the separation of the two or more lines involved (and in this differing from homology)

    Haas, O. & Simpson, G.G. (1946). Analysis of some phylogenetic terms, with attempts at redefinition. Proc. Amer. Philos. Soc. 90, 319-349: 336.


    Parallelism [...] differs from convergence in that the development of the similar features is the result of and is channelled by a common ancestry

    Blackwelder, R.E. (1967). Taxonomy: 139.


    parallelism Parallel evolution q.v.

    Lincoln, R.J., Boxshall, G.A. & Clark, P.F. (1982). A Dictionary of Ecology, Evolution and Systematics: 181.