Constraint (evolution)

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Constraints are genetic or epigenetic mechanisms that prevent undesired deviations from the blueprint during development ( ontogenesis ). In relation to evolution ( Evo-Devo ), constraints outline their course in certain bounds given by physics, morphology or phylogenesis.

Constraints are hurdles that are specified by the construction plan, such as the skeleton or lungs. They cannot be changed adaptively at will. So whales can no longer develop gills evolutionarily . Constraints limit the phenotypic evolution and at the same time determine the direction of its course. They can be physical, morphological or phylogenetic in nature. A distinction is made between external and internal constraints. The former include environmental conditions such as climate, geography, etc. In the latter context, on the one hand, genetic constraints are mentioned, such as the mechanisms of DNA repair or mechanisms of DNA unwinding during transcription ; on the other hand, the development constraints exist as internal constraints. Conrad Hal Waddington calls this phenomenon channeling .

The type and extent of how constraints can be broken and overcome play a decisive role in how evolutionary innovation can arise in development. If developmental pathways are strongly channeled, there is a buffering of genetic mutations that work towards maintaining the status quo in the phenotype. This can mean that the development is unable to respond with variation even when there is high selection pressure and that is precisely why it is forced to exceed constraints or threshold values, which then leads to increased opportunities for innovation.

On the one hand, constraints are necessary to maintain the status quo in development. On the other hand, their predefined paths or - less often - overcoming them open up opportunities for evolutionary change. Evolution thus proceeds in a dynamic equilibrium. In shaping this balancing act, constraints are themselves the subject of evolution.

literature

  • Detlef Weinich: Institutions and affect control as “constraints” of social change. Norbert Elias (1897–1990) and the theory of civilization in the light of biological-systems-theoretical evolutionary concepts. In: Würzburger medizinhistorische Mitteilungen, 24, 2005, pp. 434–473, in particular pp. 452 ff.

Individual evidence

  1. ↑ Lange, Axel (2012): Darwin's legacy under construction. Königshausen & Neumann, p. 383.
  2. ↑ West-Eberhard, Mary Jane (2003): Developmental Plastizity and Evolution, Oxford University Press, p. 25
  3. ^ Waddington, Conrad Hal (1942): Canalization of development and the inheritance of acquired characters. In: Nature. Volume 150, 1942, pp. 563-56
  4. ↑ Müller, Gerd B. & Newman, Stuart A. (2005): The Innovation Evo-Devo Agenda, Journal if Experimental Zoology, 304B, pp. 487-503
  5. ↑ Lange, A. (2012) Darwin's legacy under construction. Königshausen & Neumann. P. 54f.
  6. ^ Gould, Stephen J. & Lewontin, Richard (1979): The Spandrells of San Marco and the Panglossian paradigm: a critique of the adaptionist program. Proceedings of the Royal Societisty of London, 'B. 205, 581-598