Natural selection and adaptation

A second key point is that the success of the comparative approach usually depends on the judicious selection of study organisms. Apples must be compared to apples, if clear conclusions are to be drawn. The effects of phylogeny per se must be distinguished from the results of natural selection and adaptation. Both of these themes, which have been discussed in chapter 1, will be woven through the analysis that follows. 

Chemostats Used for Studying Natural Selection and Adaptive Evolution... 

A genetic algorithm is an adaptation procedure based on natural selection and genetics. 

Dover underlined that there is no rigid one-to-one relationship between evolutionary mechanisms and environmental processes, but noticed nonetheless that a certain correspondence does exist. He concluded therefore that adaptation is the normal result of natural selection just as exaptation is characteristic of neutral drift, and adoptation is typical of molecular drive. To our purposes, what matters is that we can indeed speak of three mechanisms of evolution the first two are natural selection and neutral drift, while the third mechanism can be called either genomic flux or molecular drive. 

Based on the information about the leaching behaviour of the material, the nature of the environment in which the material is or will be placed and an understanding of the nature and objective of the assessment, it is possible to select the most appropriate leaching test or battery of tests. It may be necessary to adapt existing tests in order to reflect more accurately the specific circumstances under consideration. The methodology behind the selection and adaptation of any tests used must be reported together with the results of testing. 

Because not all individuals in a population survive and reproduce equally well in a particular environment, some individuals contribute more offspring to subsequent generations than do other individuals. Such differential contribution of offspring resulting from variations in heritable traits was called natural selection by Charles Darwin. Natural selection is especially important because it is the only evolutionary agent that adapts organisms to their environments. 

Although natural selection is the only evolutionary agent that adapts organisms to their environments, the course of evolution has been profoundly influenced by major environmental changes, some of which had catastrophic effects. Some of these events resulted from Earth s internal processes, such as the activity of volcanoes and the shifting and colliding of continents. Others were the result of external events, such as collision of meteorites with Earth. 

Consider the first alternative, that (R) is not complete, either because some disjuncts haven t occurred yet or perhaps that there is an indefinite number of possible macromolecular implementations for (PS). This, in fact, seems to me to be true, just by virtue of the fact that natural selection is continually searching the space of alternative adaptations and counteradaptations, and that threats to the integrity and effectiveness of meiosis might in the future result in new macromolecular implementations of (PS) being selected for. However, this is no concession to antireductionism. It is part of an argument that neither (PS) nor (G) report an explanatory generalization, that they are in fact temporarily true claims about local conditions on the Earth. 

Here, past events help to explain current events via implicit principles of natural selection. Such ultimate explanations have been famously criticized as just-so stories, too easy to frame and too difficult to test (Gould and Lewontin, 1979). There is certainly something to this charge. Just because available data or even experience shows that eyespots are widespread does not guarantee that they are adaptive now. Even if they are adaptive now, this is by itself insufficient grounds to claim they were selected because they were the best available adaptation for camouflage, as opposed to some other function, or for that matter that they were not selected at all but... 

A core assumption of ultra-Darwinism is that if not all, then most observed characters must be adaptive, so as to provide the phenotypic material upon which natural selection can act. However, what constitutes a character - and what constitutes an adaptation - is as much in the eye of the beholder as in the organism that is beheld, as Gould and Lewontin pointed out in their famous paper on spandrels (Gould and Lewontin, 1979). Natural selection s continual scrutiny does not give it an a la carte freedom to accept or reject genotypic or phenotypic variation. Structural constraints insist that evolutionary, genetic mechanisms are not infinitely flexible but must work within the limits of what is physically or chemically possible (for instance, the limits to the size of a single cell occasioned by the physics of diffusion processes, the size of a crustacean like a lobster or crab by the constraints... 

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