Selection: natural

The automatic consequence of these two facts is that in any population only some can survive, and we therefore have the problem of understanding what it is that decides their survival. Chance Destiny A priori we cannot exclude that surviving is a question of luck, and in isolated cases this can indeed happen. Statistically, however, the explanation does not seem likely, and if it were true it would leave us in the most complete darkness. 

It is at this point that Darwin resorts to the two undisputahle facts from the breeders  

In nature there is an automatic selection which is continuously going on simply because variations exist between individual organisms (the breeders fact), and because not all can survive in a limited environment (Malthus fact). Darwin described the principle of natural selection at the end of Chapter 4 of On the Origin of Species, and it may be useful to read it in his own words  

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There are many other examples of interrelationship. Symmetry, for example, is of fundamental importance in the sciences and arts alike. It plays a key role in our understanding of the atomic world as well as the cosmos. The handedness of molecules, with nature selecting one... 

Even if It could be shown that RNA preceded both DNA and proteins in the march toward living things that doesn t automatically make RNA the first self replicating molecule Another possibility is that a self replicating polynucleotide based on some carbo hydrate other than o ribose was a precursor to RNA Over many generations natural selection could have led to the replacement of the other carbohydrate by D ribose giving RNA Recent research on unnatural polynucleotides by Professor Albert Eschenmoser of the Swiss Federal Institute of Technology (Zurich) has shown for example that nucleic acids based on L threose possess many of the properties of RNA and DNA... 

The function of the essential oil in the plant is not fully understood. Microscopic examination of plant parts that contain the oil sacs readily shows their presence. The odors of flowers are said to act as attractants for insects involved in pollination and thus may aid in preservation and natural selection. Essential oils are almost always bacteriostats and often bacteriocides. Many components of essential oils are chemically active and thus could participate readily in metaboHc reactions. They are sources of plant metaboHc energy, although some chemists have referred to them as waste products of plant metaboHsm. Exudates, which contain essential oils, eg, balsams and resins, act as protective seals against disease or parasites, prevent loss of sap, and are formed readily when the tree tmnks are damaged. 

Natural selection works through the complementary processes of mutation and genetic reassortment by recombination. The oligonucleotide-directed mutagenesis methods used in the foregoing examples do not allow for recombination instead, mutations are combined manually to optimize a protein sequence. Willem Stemmer at Maxygen invented a method of directed evolution that uses both mutation and recombination. This method, called... 

Provide clues about how near-real-time tactical decision aids may eventually be developed using natural selection (via genetic algorithms). 

It should be noted that apart from a passing reference to natural selection of wild-types with enhanced specific properties, the genetics of organic acid producing micro-organisms is beyond the scope of this chapter. 

It is the aim of this chapter to describe the nature, selectivity, and efficiency of initiation. Section 3.2 summarizes the various reactions associated with initiation and defines the terminology used in describing the process. Section 3.3 details the types of initiators, indicating the radicals generated, the byproducts formed (initiator efficiency), and any side reactions (e.g. transfer to initiator). Emphasis is placed on those initiators that see widespread usage. Section 3.4 examines the properties and reactions of the radicals generated, paying particular attention to the specificity of their interaction with monomers and other components of a polymerization system. Section 3.5 describes some of the techniques used in the study of initiation. 

Tubulins arose very early during the course of evolution of unicellular eukaryotes and provide the machinery for the equipartitioning of chromosomes in mitosis, cell locomotion, and the maintenance of cell shape. The primordial genes that coded for tubulins likely were few in number. As metazoan evolution progressed, natural selection processes conserved multiple and mutant tubulin genes in response to the requirements for differentiated cell types (Sullivan, 1988). 

In addition, naturally growing plants resist plant pathogen and Insect attack because resistance develops over time via natural selection (35). Also, most natural and crop plants have, as a part of their basic physical and chemical makeup, a wide array of mechanisms that help them resist pest attack. These Include chemical toxicants, repellents, altered plant nutrients, hairiness, thorns, and diverse combinations of these (35). 

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. 

European Plastics News 28,No.5, May200I,p.37-8 NATURAL SELECTION... 

Keim, K.R., Miller, F.R. Rosenow, D.T. (1983). Natural selection under diverse environments for monogenic traits in a sorghum composite. Agronomy Abstracts, pp. 69. 

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