Обессмысливание понятийной системы. Эти понятия теперь мертвые, можно делать следующие.
What is parallelism?
Robert W. Scotland 2011
Although parallel and convergent evolution are discussed extensively in technical articles and textbooks, their meaning can be overlapping, imprecise, and contradictory.
The meaning of parallel evolution in much of the evolutionary literature grapples with two separate hypotheses in relation to phenotype and genotype, but often these two hypotheses have been inferred from only one hypothesis, and a number of subsidiary but problematic criteria, in relation to the phenotype. However, examples of parallel evolution of genetic traits that underpin or are at least associated with convergent phenotypes are now emerging. Four criteria for distinguishing parallelism from convergence are reviewed. All are found to be incompatible with any single proposition of homoplasy. Therefore, all homoplasy is equivalent to a broad view of convergence. Based on this concept, all phenotypic homoplasy can be described as convergence and all genotypic homoplasy as parallelism, which can be viewed as the equivalent concept of convergence for molecular data.
Parallel changes of molecular traits may or may not be associated with convergent phenotypes but if so describe homoplasyattwobiologicallevelsFgenotype andphenotype.
Parallelism is not an alternative to convergence, but rather it entails homoplastic genetics that can be associated with and potentially explain, at the molecular level, how convergent phenotypes evolve.
A recurring theme in the discussions cited above is that parallel evolution of the same phenotypic trait which often but not exclusively occurs in closely related monophyletic lineages, represents something distinct from convergence, as the genetics and phylogenetic context (community of inher-itance, homologous generators) that underpin parallel phe-notypic homoplasies are more extensive than for convergent phenotypic homoplasies. This view would implicitly consider, analogy, convergence, parallelism, and homology as stages along a continuous spectrum from less to more shared ge-netics determined in part by the closeness of phylogenetic relations. In other words, analogies and convergences have few, if any genes in common whereas parallelism, and par-ticularly homology, are both largely underpinned by the same genetic mechanisms. However, the view that homologous structures can be underpinned by nonhomologous genotypes and vice versa (de Beer 1971) coupled with recent discoveries that homologous genes can underpin widely disparate anal-ogous morphologies (Panganiban et al. 1997; Shubin et al. 1997, 2009; Panganiban and Rubenstein 2002) calls this over-simplif i ed view into question. In short, the concept of deep homology (Shubin et al. 1997, 2009) for examples in which ‘‘the sharing of the genetic regulatory apparatus that is used to build morphologically and phylogenetically disparate animal features,’’ has developed because analogous and homo-plastic phenotypes can be regulated and determined by varying degrees of similar or different underlying genetics.
The concepts of deep homology and parallelism are therefore closely related but both require precision in their use if they are to be more than a simple loose description of associated genotypic and phenotypic change.
The view presented in this article provides a simplified framework for what evolutionary and developmental biologists have to explain in terms of comparative anatomy: the unique evolution of correspondent traits F novelty/synapomorphy F and the evolution of independent traits F convergence or its molecular equivalent parallelism F (Fig. 3). This clarif i cation of the use of the terms convergence and parallelism involves restricting convergence to describing the inde-pendent evolution of correspondent phenotypes and view parallelism as describing the homoplasy of genotypes (Figs. 3 and 5). These two levels of homoplasy from the phenotype and genotype can then be combined to describe parallel evo-lution that is parallel genetic traits that underpin or are at least associated with phenotypic convergence. Convergence is about phenotypes, whereas parallelism, just like deep homology, is a conditional phrase that attempts to describe the relationship between genotype and phenotype. Convergent evolution involves one hypothesis whereas parallel evolution of genetic traits that underpin convergence of the phenotype, comprises two. When the term parallelism is restricted to all instances of genotypic homoplasy (5the genotypic equiva-lent of phenotypic convergence), the meaning of parallel evo-lution becomes clear and unambiguous. One possible objection to this framework is that the use of the term par-allelism to describe all genotypic homoplasy is too broad and that parallel genetic traits should be distinguished from genetic traits due to convergence and reversal. Rokas and Carroll (2008) distinguish molecular substitutions due to reversal to the pleseiomorphic state, convergence from different ancestral states and identical parallel changes to the same state, whereas Bull et al. (1997) adopted a broad view of convergence to describe all genotypic homoplasy. Despite terminological dif f erences, these studies (Bull et al. 1997; Rokas and Carroll 2008) are clear in their use of these terms.
If parallelism is a term used to describe all instances of ge-notypic homolpasy, there is no reason why the shared pres-ence of the same or dif f erent ancestral character states cannot be explicitly part of that framework where appropriate. The widely dif f erent use of these termsFconvergence, reversal, and parallelismFto describe dif f erent facets of molecular ho-moplasy at the DNA and amino acid sequence level conveys the impression that most authors don’t distinguish fundamentally different underlying processes.