In those organisms dying out. Therefore, only the good

In 1859, Charles Darwin, an English scientist,
published his book entitled, “Origin of Species”. He was 50 years old at the
time when he proposed the theory of evolution by Natural Selection. The theory
he projected simply stated that the species best adapted to reproduce and
survive were, in a sense, nature-selected. As a result, this led to
evolutionary changes, since different genotypes and phenotypes of species had
consistent differences in their survival and reproduction rates or fitness.                                                                                

Darwin’s Theory was centered on four principles: Variation in traits, Overproduction,
Selection and Reproduction by adaptation. Variation allowed for the adaptation
of species with a particular phenotype to their environment. The more genetic
variation the more the variation of the phenotype, since phenotypic variation
is due to heritable genetic variation. New alleles can either be advantageous
or disadvantageous, by either increasing an organism’ ability to have high
fitness and therefore ensuring the survival of the allele in the population or
decreasing the organism’s fitness by being detrimental and therefore resulting
in those organisms dying out. Therefore, only the good mutations are
incorporated into the evolutionary process and the bad mutations are removed. Simply put, Genetic variation allows for evolution by natural
selection by either decreasing the frequency of the alleles or increasing it.
Variation can occur in many different ways, one such is mutation, which is
being explained thus far. Mutations are permanent alteration to a nucleotide
sequence of a DNA molecule, which is random and unpredictable. Most mutations
may have no effect on the organism, while some mutations may either be beneficial
or harmful. An example of harmful mutation is a fly mutated with the Hox gene,
this gene transforms one body part into another. A beneficial mutation in
humans is our ability to have trichromatic vision, which means we are able to
see three colours, while many animals may be monochromatic or dichromatic.

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Another of Darwin’s principle which was
incorporated in his theory of evolution was Overproduction. Each species’ generation
usually would have more offspring to resources ratio, and as a result all will
not survive. To continue life depends on their ability to adapt and those


organisms in the species with the advantageous
trait will help them to survive and hence, reproduce. The organisms which will
survive as a result of their advantageous will produce more offspring which are
likely to inherit their traits, as well. Therefore, once a trait allows for the
increase of the likelihood of reproduction it is a key for natural selection.

Another principle necessary for evolutionary
changes by Natural Selection is the modes of selection. The modes of Selection
are: – Directional Selection, Stabilizing Selection, Sexual Selection and
Disruptive Selection, etc.  In
Directional Selection, there is a shift to the extreme phenotype since may have
been favoured over other phenotypes, this change is quite noticeable since it
is dramatic e.g. short neck turtles would have evolved to long neck turtles to
better reach their food. In Stabilizing Selection, there are variations in the
phenotypes to which the average phenotype is favoured e.g. a medium sized baby
is said to be better adapted than a small or larger baby. In Sexual Selection
the organism’s ability to copulate with a mate allows for the likelihood for
the increase in the trait. In this the trait is in competition with another of
the same species, e.g. peacocks with the big and beautiful feathers have a
higher probability  to be picked by a
respective mate, than the probability of a peacock with small and little
amounts of feathers has.

The last factor necessary for Natural Selection
is Reproduction by adaptation. Adaptation is simply the process whereby an
organism is better suited in its environment conditions. In the end,
individuals that possess the more favourable traits will be able to reproduce
and hence passing those traits down to its offspring, making them too able to
reproduce. Those organisms which possess the unfavourable traits, to which they
are unable to adapt to the environmental conditions will not survive and,
therefore will be unable to reproduce. Overtime, the less desirable or
unfavourable traits will lessen and the species entirely will become stronger
and better adapted.

 In the
end, those organisms with particular features that adapt them to their
environment will have a high fitness. Evolutionary changes by natural selection
will be a product once you have Variation in traits, Overproduction, Selection
and Reproduction by Adaptation