Natural Selection vs Genetic Drift
Both natural selection and genetic drift lead to evolution process by varying the gene frequency of a population over time. Both these processes are involved in evolution and are not mutually exclusive. However, natural selection is the only process, which selects the best adaptive organism to the environment, and genetic drift reduces the genetic variation.
These variations in genes or alleles are inheritable and genetic variation can be resulted by mutation, gene flow and sex.
Natural Selection
Natural selection is a hypothesis proposed by Darwin, where most adaptive organisms are selected by the environment gradually. Natural selection occurs when individuals are genetically varied, that variation makes some individuals better than others, and those superior traits are heritable.
This process occurs through mutations, which occurs in individuals randomly due to various reasons. Because of these mutations, individual may have the advantage beyond the environmental challenges. Individual with this mutation may have better adaptation to the environment than others. For an example, the superior trait will help to escape from predators running faster than other individuals. They can reproduce more than other individuals and trait will pass to the second generation and the evolving of new species happens. The frequency of the new trait will increase in the genome and this process is called natural selection or survival of the fittest organisms.
Genetic Drift
The variation in allele frequencies within a population due to random sampling is simply called genetic drift or Sewall Wright effect. Due to random sampling, subset of the population is not necessarily a representative of the population. It might be skewed to either direction. Smaller the population, the effect of random sampling causes genetic drift than a larger population. Some alleles become more common while they are being selected over and over again, and some may disappear from the small, isolated populations. This genetic drift or disappearance of the allele is unpredictable (Taylor et al, 1998).
The new generations may be diverge form of the parental population thus resulting either extinction of the population or making more adaptive species to the environment. However, in a large population, this effect can be considered as negligible. Genetic drift does not select the adaptive organism like natural selection.
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What is the difference between Natural Selection and Genetic Drift? • The major difference between natural selection and genetic drift is that the natural selection is a process where more adaptive species are selected in response to the environmental challenges, whereas genetic drift is a random selection. • Natural selection occurs due to environmental challenges, whereas genetic drift does not occur due to environmental challenges. • Natural selection ends up with selecting the more successive trait over the detrimental trait, whereas due to genetic drift important alleles may disappear completely. • Natural selection increases the frequency of the trait more adaptive to the environment, whereas genetic drift rarely results in more adaptive species to the environment. • Natural selection increases genetic variation, whereas genetic drift does not increase genetic variation compared to natural selection. Some times genetic drift causes some variants to be extinct completely.
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References:
http://evolution.berkeley.edu/evosite/evo101/IIICGeneticvariation.shtml
http://faculty.clintoncc.suny.edu/faculty/michael.gregory/files/