NATURAL SELECTION

NATURAL SELECTION
The chief contribution of Darwin was the identification of natural selection as the force directing organic evolution. Natural selection is the differential reproduction of various genotypes of a natural population in response to the natural environment in which the population exists. Clearly this concept of natural selection differs from the original Darwinian concept, which assumed the natural selection to weed out unfit genotype from populations, most likely by causing their death. But the modern day concept of natural selection perceives it as reducing the rates of reproduction of unfit genotypes rather than causing their elimination by death. It may also be emphasized that selection does not act on genes or alleles themselves; it act on the phenotypes produced by them. Similarly, selection seldom operates on individuals genes; it does not soon gene combinations present in the different individuals of a population. In other words, selection generally acts on the total phenotype of individuals not on the phenotype produced by the individual genes. In addition, a gene may be detrimental in one genetic background, while it may be beneficial in another one. In other words, the selective values of gene changes with environment.