Natural selection is a process that demonstrates that
evolution is not just based on chance but other factors and that not all
individuals will survive. The survival of individuals is determined by their
surroundings and the compatibility of their characteristics with those
surroundings. In a population, there will be overproduction of offspring and in
those offspring, there will be variations from one individual to another due to
genetic differences. Using the snails as
an example, each individual has shell that varies in color (pink, brown,
yellow) and number of bands. These
variations may be useful if they allow an individual to have a better chance of
survival or may be harmful if they make it difficult to survive. The different colored
shells have different thermal properties. Darker shells (brown and pink) are
more efficient in absorbing solar radiation than do the yellow shells. As a
result, darker snails are better suited to cooler climate as they use the heat
to keep themselves warm, while snails with yellow shells are better suited to
warmer climates because they can tolerate the heat. Snails with yellow shell
also tend to live in open grassland and pink and brown unbanded shells in
woodland. This is because yellow snails are more heavily predated in woodland
due to their bright colors against the dark background of the woodland floor.
As opposed to brown and pink snails that are better camouflaged and able to
avoid predation. Since their genetic characteristics are poorly adapted for
their environment, there will be a decrease in snails with yellow shells in woodlands
and decrease in snails with brown/pink shells in grassland because they will
have less of a chance of surviving to maturity. The better-adapted individuals
(yellow shell snails in grasslands and brown/pink shell snails in woodlands)
will survive to adulthood since they have a better chance to reproduce and to
pass on their successful genetic characteristics to the next generation.
Another case of natural selection is the deer mouse in the
Sand Hills of Nebraska and is one of the quickest-evolving examples of natural
selection in animals. Their adaptation in variations of fur color is similar to
the variations in the shell color of the snails in avoiding predation in their
habitat. The deer mouse is normally dark-brown which is suitable for mice
living in the woods where it is dark and they can blend in with the
surroundings thus hiding from predators. However, when these dark-colored mice
are in the Sand Hills, it would be easily spotted by the predators against the
area’s light terrain. As a result, over time the deer mouse with the darker
colors will die and the deer mouse with the lighter colors will survive and
pass on these preferable characteristics to its offspring. Over many
generations, the accumulation of changes in the heritable characteristics of a
population results in evolution and the gene pool has changed. The mice living
in Sand Hills quickly evolved lighter coloration. Light coloration arises from
increased activity in a single gene which is called Agouti and is being
inherited through several generations. This increased expression is associated
with the deletion of a single amino acid, a process that appears to be under
natural selection. This Agouti mutation generates wider pale bands on dorsal
hairs, making the entire animal appears golden rather than brown. Scientists predicted that predation would
drive virtually all individuals in the area toward pale coloration within 8,000
years.
Ecology is the study of the relationships that organisms
have with other organisms and their environment. As we can see from the
examples of the snails and mouse, organisms interact with other organisms and
the environment in ways that will alter the characteristics of their
variations. Some characteristics will be preferable over the other to maintain
the survival of the organism. As a result, over a period of time and
generations, the characteristics that were influenced will be altered which
results in evolution. Evolution is defined as the process of cumulative change
in the heritable characteristics of a population. Evolution is possible since
these preferable characteristics are passed on to successive generations
through genetics thus impose changes in the gene pool of the population.
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