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Functional Constraint and Molecular Evolution

  1. Donald R Forsdyke

Published Online: 16 JUL 2012

DOI: 10.1002/9780470015902.a0001804.pub3



How to Cite

Forsdyke, D. R. 2012. Functional Constraint and Molecular Evolution. eLS. .

Author Information

  1. Queen's University, Ontario, Canada

Publication History

  1. Published Online: 16 JUL 2012


While having one or more specific functions, macromolecules have collective functions (e.g. Donnan equilibrium and aggregation pressure), and general functions (e.g. contribution to organism weight). Successful molecular evolution requires an appropriate balance between the constraints on these functions, which arise from selective pressures acting at the levels of conventional phenotypes (natural selection) and genome phenotypes (reprotypic selection). Genome-wide constraints include fold pressure (nucleic acid stem-loop extrusion pressure) and GC-pressure (the pressure for a certain base composition). When these bring about within-genome reprotypic selection (hybrid sterility), there is the potential for new species to emerge (speciation). Local constraints include protein pressure (the pressure to encode a protein) and purine-loading pressure (purine-rich messenger ribonucleic acid (mRNA) synonymous strands). As more pressures are identified, arguments for neutral evolution weaken.

Key Concepts:

  • Molecules have specific, collective and general functions.

  • Most macromolecules function by virtue of their higher ordered structure.

  • Nucleic acids have both structural and templating functions.

  • Each species achieves its own balance between the competing demands (constraints) of external and internal environments.

  • The organismal phenotype comprises the classical phenotype and the genome phenotype.

  • Natural selection operates on the classical phenotype.

  • Reprotypic selection operates on the genome phenotype.

  • By balancing natural and reprotypic selection mechanisms, the ‘hand of nature’ resolves conflicts between functions.


  • conflict resolution;
  • degenerate code;
  • GC rule;
  • neutralism;
  • purine-loading;
  • speciation