Pseudaptations and the Emergence of Beneficial Traits
There is increasing evidence for the emergence of some beneficial traits in biological systems in the absence of direct selection. Many of these encompass mutational robustness, which increasingly appears to arise as a by-product of natural selection, as
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Pseudaptations and the Emergence of Beneficial Traits Steven E. Massey
Abstract There is increasing evidence for the emergence of some beneficial traits in biological systems in the absence of direct selection. Many of these encompass mutational robustness, which increasingly appears to arise as a byproduct of natural selection, as a consequence of the biased incremental change of complex biological systems. Understanding the emergence of robustness in disparate biological systems is facilitated by the use of graph theory and the concept of connectivity. A particular case that is explored here is that of the standard genetic code (SGC). The SGC is arranged so that mutations tend to result in conservative as opposed to radical amino acid changes, a property termed “error minimization”. A commonly cited explanation for this property is the “Adaptive Code” hypothesis, which proposes that error minimization has been directly selected for. However, it is shown that direct selection of the error minimization property is mechanistically difficult. In addition, it is apparent that error minimization may arise simply as a result of code expansion, this is termed the “emergence” hypothesis. The emergence of error minimization in the genetic code is likened to other biological examples, where mutational robustness arises from the innate dynamics of complex systems; these include neutral networks and a variety of subcellular networks. The concept of “biased incrementalism” is introduced to account for the emergence of robustness in these diverse systems, while the term “pseudaptation” is used for such traits that are beneficial to fitness, but are not directly selected for.
S.E. Massey Biology Department, University of Puerto Rico – Rio Piedras, P.O. Box 23360, San Juan, Puerto Rico 00931, USA e-mail: [email protected]
P. Pontarotti (ed.), Evolutionary Biology – Concepts, Molecular and Morphological Evolution, DOI 10.1007/978-3-642-12340-5_5, # Springer-Verlag Berlin Heidelberg 2010
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5.1
S.E. Massey
Adaptive Evolution and Natural Selection
The modern definition of an adaptation is tautological in relation to natural selection; from Mayr’s book “What Evolution Is” (Mayr 2001), adaptations are beneficial traits that arise by natural selection, of if they occur by chance are maintained by natural selection. From a panselectionist perspective, all beneficial phenotypes are to be regarded as adaptations, arising from natural selection. However, it may be argued that the definition of “adaptation” is not inviolate; indeed, it is worth remembering that until the modern synthesis natural selection was not widely accepted as the predominant force behind adaptive evolution; the so-called “eclipse of Darwinism” (Huxley 1942). The theme of this work is to clarify the definition of adaptation, in the context of natural selection, and to examine examples of beneficial traits that have arisen in the absence of direct selection, and how they should be defined.
5.2
Emergence as a By-Product of Natural Selection
Emergenc
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