Mechanismsof evolution are the mechanisms that change allele frequencies in populations. The first mechanism is natural selection. This iswhen one allele is favored over another depending on the particularenvironment. Then the selected allele that causes the better adapted phenotypeis passed on to offspring and becomes more common in a population and the allele increases in frequency.
The second mechanism isgenetic drift. Genetic drift is when allele frequencies change due to chance orrandom events, not due to natural selection! Populations are more likely toevolve by genetic drift if they are small which is when a chance event may havea large effect. A small population may arise & evolve by genetic drift whena population bottleneck occurs which is when some random event destroys most ofa population, leaving a small random sample of individuals behind with adifferent allele frequency from the original population. Endangered speciesarise from population bottlenecks and become small populations that are thensusceptible to the effects of genetic drift.
An example of this is the Floridapanther. (Kimura 1970)The third mechanism forevolution is mutation. Mutations are rare and occur about 1 in 100,000nucleotides per cell division. Mutations can only affect evolution if they areheritable or only if they exist in gametes. Mutations may increase survival, orbe lethal, or be deleterious so they may or may not appear or increase in thepopulation. Also, mutations may be “silent” or “neutral” and not affected bynatural selection so they do not affect survival one way or another. Non-random mating isanother mechanism of evolution, allele frequencies in a population may changeby biased mate selection. One example of assortative or non-random mating isinbreeding or mating between closely related individuals.
There are two typesof assortative mating (A.M.): Positive A.M. which is when similar-lookingpartners mate and Negative A.M. which when dissimilar-looking partners mate.
The bottom line is that both inbreeding and positive A.M. increase homozygosityand cause a loss of genotypic diversity.
(Li 1955)All in all, there aremultiple mechanisms of evolution which suggest and confirm the theory ofevolution.