Darwinian selection

Dyson s model has been the subject of careful criticism as well as well-meaning agreement. Shneior Lifson (1997) found fault in particular with Dyson s assumption that metabolism (and other properties) could have developed without natural selection. In his third assumption, Dyson postulates that There is no Darwinian selection. Evolution of a molecule population occurs via genetic drift (Dyson, 1999). Lifson (1997) points out that, while Dyson stresses the role of primitive metabolism, its adaptability, error tolerance etc., he himself considers that such properties can only evolve via natural selection. 

In summary, we see that the study of nonequilibrium systems gives us some understanding of the process of evolution. The appearance of a certain type of organization or order is through fluctuations and kinematic considerations. In general we cannot associate a strict optimization principle to evolution there is no strict Darwinian selection of the fittest. 

A desired level of protein synthesis should be obtainable within a short time after induction. Rapid induction is desirable for two reasons First, a short induction period reduces the time for each round of screening. Second, and most important, when the cells are kept in an induced state for a shorter period, Darwinian selection of faster growing non-target clones is minimized. 

The experimental discipline that is now known as combinatorial chemistry—although it is also known by such evocative terms as test tube or in-vitro evolution—arose almost 30 years ago. At that time, RNA evolution experiments showed that it was possible to create selection-pressure conditions in an experimental setting that caused certain species of RNA, but not others, to survive from one generation to the next [2], This work was complemented by advances of theories on how biopolymers organize themselves and change over time under specific conditions [3]. About 13 years ago, the use of evolution and Darwinian selection was proposed for RNA [4] and for proteins [5] in an... 

Genetic programming [137] is an evolutionary technique which uses the concepts of Darwinian selection to generate and optimise a desired computational function or mathematical expression. It has been comprehensively studied theoretically over the past few years, but applications to real laboratory data as a practical modelling tool are still rather rare. Unlike many simpler modelling methods, GP model variations that require the interaction of several measured nonlinear variables, rather than requiring that these variables be orthogonal. 

This theory, in Kimura s own words, states that The great majority of evolutionary mutant substitutions are not caused by positive Darwinian selection but by random fixation of selectively neutral or nearly neutral mutants (it is important to underline that the adjective neutral does not mean without function it only means that a mutation is adaptively indifferent, i.e. it is neither better nor worse than the previous one in respect to the organism s adaptation to the environment). 

So far, we have constructed an unsatisfying picture of the earliest days of an RNA world although some prebiotic mechanisms may exist for the untemplated formation of oligonucleotides, these molecules would have been short, would have contained a variety of monomers besides ribotides, and could not have been faithfully copied by the template-directed polymerization of monomers. Given this model, it is difficult to imagine the accumulation of RNA sequences necessary for the Darwinian selection of a multitude of active ribozymes. Nevertheless, these precursors may have been adequate for the first critical step in the formation of life the formation of an RNA replicase. 

Spin more than one hypothesis. If there s something to be explained, think of all the different ways in which it could be explained. Then think of tests by which you might systematically disprove each of the alternatives. What survives, the hypothesis that resists disproof in this Darwinian selection among "multipleworking hypotheses," has a much better chance of being the right answer than if you had simply run with the first idea that caught your fancy. 

Whether life started with the formation of vesicular structures or became encapsulated at a later stage is still a matter of much debate. What seems likely is that some kind of protocells already existed by the time RNA appeared. This contention is based on the assumption, which looks reasonable, that the RNA molecules that launched the RNA world and developed protein synthesis must have emerged by Darwinian selection. A direct selection process, based on the stability and... 

Although much remains to be learned about protein stmcture and evolution, all the available evidence now supports the conclusion that the folds represent a finite natural ensemble of forms, determined by a hierarchic set of physical constmctional mles that arise out of the fundamental properties of linear polymers made up of the twenty proteinaceous amino acids, and assemble into their native forms like a set of crystals through a series of phase transitions (Scheraga, 1963 Florey, 1969). And, like any other set of natural forms, such as atoms or crystals, the folds are genuine universals that are antecedent to biology and thus to Darwinian selection. In short, the universe of protein forms can be accounted for by physical... 

How are we to account for this universality within the remarkable diversity both of environments and of relative reaction kinetics within organisms Two interpretations exist, one based on an extreme controlling role for gene-encoded catalysis and pure Darwinian selection, and the other based on a continuation from physical chemistry to core metabolism. 

Lee, Y.-H. and Vacquier, V.D. (1992). The divergence of species-specific abalone sperm lysins is promoted by positive Darwinian selection. Biol. Bull. 7S2 97-105. 

Smith, N.H., Maynard-Smith, J., and Spratt, B.G. (1995). Sequence evolution of the porB gene of Neisseria gonorrhoeae and N. memingitidis Evidence of positive Darwinian selection. Mol, Biol. Evol. 72 363-370. 

Swanson, W.J. and Vacquier, V.D. (1995b). Extraordinary divergence and positive Darwinian selection in a fusagenic protein coating the acrosomal process of abalone spermatozoa. Proc. Natl. Acad. Sci. USA. 92 4957-4962,... 

Vacquier, V.D., Swanson, W.J., and Lee, Y.-H. (1997). Positive Darwinian selection on two homologous fertilization proteins What is the selective pressure driving their divergence J. Mol. Evol. 44(Suppl. 1) S15-S22. 

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