Mosaic evolution

Mosaic evolution

Mosaic evolution (or modular evolution) is the concept that evolutionary change takes place in some body parts or systems without simultaneous changes in other parts.[1] Another definition is the "evolution of characters at various rates both within and between species".[2]408 Its place in evolutionary theory comes under long-term trends or macroevolution.[2]

By its very nature, the evidence for this idea comes mainly from palaeontology. It is not claimed that this pattern is universal, but there are now a wide range of examples from many different taxa. Some examples:

  • Hominid evolution: the early evolution of bipedalism in Australopithecines, and its modification of the pelvic girdle took place well before there was any significant change in the skull, or brain size.[3][4]
  • Mammalian evolution, especially during the Mesozoic is undoubtedly one of the best examples.[10][11][12]


In the neodarwinist theory of evolution, as postulated by Stephen Jay Gould, there is room for differing development, when a life form matures earlier or later, in shape and size. This is due to allomorphism. Organs develop at differing rhythms, as a creature grows and matures. Thus a "heterochronic clock" has three variants: 1) time, as a straight line; 2) general size, as a curved line; 3) shape, as another curved line.[13]

When a creature is advanced in size, it may develop at a smaller size; alternatively, it may maintain its original size or, if delayed, it may result in a larger sized creature. That is insufficient to understand heterochronic mechanism. Size must be combined with shape, so a creature may retain paedomorphic features if advanced in shape or present recapitulatory appearance when retarded in shape. These names are not very indicative, as past theories of development were very confusing. [13]

A creature in its ontogeny may combine heterochronic features in six vectors, although Gould considers that there is some binding with growth and sexual maturation. A creature may, for example, present some neotenic features and retarded development, resulting in new features derived from an original creature only by regulatory genes. Most novel human features (compared to closely related apes) were of this nature, not implying major change in structural genes, as was classically considered.[13]

See also


  1. ^ King R.C. Stansfield W.D. & Mulligan P.K. 2006. A dictionary of genetics. 7th ed, Oxford University Press. p286 ISBN 0195307615
  2. ^ a b Carroll R.L. 1997. Patterns and processes of vertebrate evolution. Cambridge University Press. ISBN 052147809X
  3. ^ Stanley S.M. 1979. Macroevolution: pattern and process. Freeman, San Francisco. p154 ISBN 0716710927
  4. ^ Jurmain, Robert. et al. 2008. Introduction to Physical Anthropology. Thompson Wadsworth. p479
  5. ^ Foster, Michael and Lankester, E. Ray (eds )1898–1903. The scientific memoirs of Thomas Henry Huxley. 4 vols and supplement, Macmillan, London ISBN 1432640119
  6. ^ Barnovsky A.D. 1993. Mosaic evolution at population level in Microtus pennsylvanicus. In Morphological changes in Quarternary mammals of North America. ed R.A. Martin & A.D. Barnovsky. Cambridge University Press. pp24–59
  7. ^ Lü J., Unwin D.M., Jin X., Liu Y. and Ji Q. 2010. Evidence for modular evolution in a long-tailed pterosaur with a pterodactyloid skull. Proceedings of the Royal Society B, 277(1680): 383-389. doi:10.1098/rspb.2009.1603 PMID 19828548
  8. ^ MacFadden, Bruce J (2003 digitization of 1999 reprint). Fossil horses: systematics, paleobiology, and evolution of the Family Equidae. Cambridge: Cambridge University Press. ISBN 0-521-47708-5. Retrieved 6 June 2010 
  9. ^ Maynard Smith, John 1993. The theory of evolution. Cambridge University Press. 3rd ed + new Introduction. pp285–290 ISBN 0521451280
  10. ^ Kermack, D.M.; Kermack, K.A. (1984). The evolution of mammalian characters. Croom Helm. ISBN 079915349. 
  11. ^ Kemp T.S. 2005. The origin and evolution of mammals. Oxford University Press, Oxford. ISBN 0-19-850761-5
  12. ^ Kielan-Jaworowska, Zofia; Richard L. Cifelli and Zhe-Xi Luo 2004. Mammals from the Age of Dinosaurs: origins, evolution, and structure, Columbia University Press, New York. ISBN 0-231-11918-6
  13. ^ a b c Jay Gould, S. 1977. Ontogeny and phylogeny. Belknap Press of Harvard University Press.

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