of evolution are the mechanisms that change allele frequencies in populations.
The first mechanism is natural selection. This is
when one allele is favored over another depending on the particular
environment. Then the selected allele that causes the better adapted phenotype
is passed on to offspring and becomes more common in a population and the allele increases in frequency.
The second mechanism is
genetic drift. Genetic drift is when allele frequencies change due to chance or
random events, not due to natural selection! Populations are more likely to
evolve by genetic drift if they are small which is when a chance event may have
a large effect. A small population may arise & evolve by genetic drift when
a population bottleneck occurs which is when some random event destroys most of
a population, leaving a small random sample of individuals behind with a
different allele frequency from the original population. Endangered species
arise from population bottlenecks and become small populations that are then
susceptible to the effects of genetic drift. An example of this is the Florida
panther. (Kimura 1970)
The third mechanism for
evolution is mutation. Mutations are rare and occur about 1 in 100,000
nucleotides per cell division. Mutations can only affect evolution if they are
heritable or only if they exist in gametes. Mutations may increase survival, or
be lethal, or be deleterious so they may or may not appear or increase in the
population. Also, mutations may be “silent” or “neutral” and not affected by
natural selection so they do not affect survival one way or another.
Non-random mating is
another mechanism of evolution, allele frequencies in a population may change
by biased mate selection. One example of assortative or non-random mating is
inbreeding or mating between closely related individuals. There are two types
of assortative mating (A.M.): Positive A.M. which is when similar-looking
partners mate and Negative A.M. which when dissimilar-looking partners mate.
The bottom line is that both inbreeding and positive A.M. increase homozygosity
and cause a loss of genotypic diversity. (Li 1955)
All in all, there are
multiple mechanisms of evolution which suggest and confirm the theory of