"Natural selection" Summary

Reference: Wikipedia, Natural selection

Natural selection is a natural law by which genetically heritable traits become more or less common in a population over successive generations. This selection in interaction with the production of variation, the possible genetic fixation process and possibly, in several cases, whith little epigenetic process determine the evolution of the species.

The natural genetic variation within a population of organisms means that some individuals will survive and reproduce more successfully than others in their current environment. For example, the peppered moth exists in both light and dark colors in the United Kingdom, but during the industrial revolution many of the trees on which the moths rested became blackened by soot, giving the dark-colored moths an advantage in hiding from predators. This gave dark-colored moths a better chance of surviving to produce dark-colored offspring, and in just a few generations the majority of the moths were dark. Factors which affect reproductive success are also important, an issue which Charles Darwin developed in his ideas on sexual selection.

Natural selection acts on the phenotype, or the observable characteristics of an organism, but the genetic (heritable) basis of any phenotype which gives a reproductive advantage will become more common in a population (see allele frequency). Over time, this process can result in adaptations that specialize populations for particular ecological niches and may eventually result in the emergence of new species. In other words, natural selection is an important process (though not the only process) by which evolution takes place within a population of organisms. As opposed to artificial selection, in which humans favor specific traits, in natural selection the environment acts as a sieve through which only certain variations can pass.

Natural selection is one of the cornerstones of modern biology. The term was introduced by Darwin in his influential 1859 book On the Origin of Species,[1] in which natural selection was described as analogous to artificial selection, a process by which animals and plants with traits considered desirable by human breeders are systematically favored for reproduction. The concept of natural selection was originally developed in the absence of a valid theory of heredity; at the time of Darwin's writing, nothing was known of modern genetics. The union of traditional Darwinian evolution with subsequent discoveries in classical and molecular genetics is termed the modern evolutionary synthesis. Natural selection remains the primary explanation for adaptive evolution.

Contents
1 General principles
1.1 Nomenclature and usage
1.2 Fitness
1.3 Types of selection
1.4 Sexual selection
2 Examples of natural selection
3 Evolution by means of natural selection
3.1 Speciation
4 Historical development
4.1 Pre-Darwinian theories
4.2 Darwin's theory
4.3 Modern evolutionary synthesis
5 Impact of the idea
5.1 Cell and molecular biology
5.2 Social and psychological theory
5.3 Information and systems theory
6 Genetic basis of natural selection
6.1 Genotype and phenotype
6.2 Directionality of selection
6.3 Selection and genetic variation
6.3.1 Mutation selection balance
6.3.2 Genetic linkage
7 See also
8 References
9 Further reading
10 External links
To be continued.
20:13 　2010/08/21