Download Natural Selection Paper

Natural Selection Paper
Natural selection is considered one of the most important processes for a variety of species and
the environment which allows the fittest organisms to produce offspring. To prevent a species
from extinction, it is necessary for them to adapt to the surrounding environment. The species
which have the ability to adapt to new surroundings will be able to pass their genes through
reproduction. Within the process of natural selection, it is possible for the original genetic
make-up of a species to become altered. The team will report on the different processes of
basic mechanisms of evolution, how natural selection results in biodiversity and why
biodiversity is important to continued evolution. The sources of genetic variation such as
mutations and sexual recombination will also be reviewed. Mechanisms of Evolution
It is said that biology “came of age” when Charles Darwin published “On the Origin of Species
by Means of Natural Selection”. In this book Darwin expressed his concept on the mechanism
of evolution: natural selection. He felt that a population could change over generations if
organisms that have certain heritable traits left more offspring than other organisms in that
population. The result of this is evolutionary adaptation is where populations increase in traits
that are suited to the environment. Evolution is when the genetic makeup of a population
changes over time to adapt to its environment. Darwin found evidence of natural selection
when he sailed from Great Britain along the South American coastline in 1831. He noticed
various adaptations in the organisms inhabiting South America. He realized that the plants and
animals were distinctly different from the organisms in Europe. Upon examination of different
fossils on the South American continent he observed that the fossils were different from the
modern species and yet there was still a resemblance between the fossils and the modern
organisms. In his book The Origin of Species Darwin stated that as descendants of the earliest
life forms spread into various habitats, over time, they accumulated different adaptations to
diverse ways of life. In his view, evolution is like a tree with the various branches representing
the evolution of different traits from a common trunk. (this needs to be cited) How Natural
Selection
results
in
Biodiversity
Natural selection is based upon a couple of important facts that result in unequal reproductive
success. First, overpopulation and competition will affect the population of any species and
individual variation will make some individuals more likely to survive and pass on these
variations to their offspring (Campbell, et al, 2007). Second, adaptation is a mechanism for
evolution due to generations of natural selection weeding out individuals that do not have the
trait that is dominant at survival. Biodiversity is short for biological diversity which consists of
three main concepts: Ecosystem variety, species variety, and genetic variation within the
species. These three biodiversity variables connect closely with the concepts of natural
selection.
Natural selection results in biodiversity in the following ways; overpopulation and competition
are the primary considerations in the operation and success of an ecosystem. If there is no
diversity in the species that exist in the ecosystems, there will be overpopulation and
competition for the same foods and habitat. By the adaptation of the variety of species to noncompeting food and habitat, an ecosystem can support itself. The species that successfully
adapt to the non-competition will be more successful at survival and natural selection occurs.
An example of adaptation and sharing an ecosystem is the savannah of Africa. Each of the
species interacts with its environment in a cycle of giving nutrients and taking nutrients. The
diverse species co-exist and actually contribute in some degree to the welfare of the other
species. When biodiversity and adaptation do not occur, the species compete with each other
until the populations are all at risk. Why Biodiversity is Important to Continued Evolution
The three levels of biodiversity are as follows: diversity of the ecosystems, diversity of species
within the communities and diversity within species. The loss of species within the ecosystems
and within the community can cause a catastrophic result, as species live and feed on other
species. Species close to extinction are endangered species, therefore protecting them from
predators and offering the chance to reproduce and repopulate. Unfortunately, with little
support within the environment, a species can become extinct due to population density.
Proper monitoring of an endangered species is required in order to keep species actively
reproducing and changing with the environment around them. There is another side to the
biodiversity of the evolutionary field, as the population weakens the species start the
inbreeding of smaller populations, thus playing a role in the extinction of a species. Inbreeding
is reproduction among members of a species that are genetically similar. The genetic
inbreeding is designed to bolster populations of species whose numbers are in decline.
However, when only a few species or varieties of a species are cultivated or survive, the genetic
diversity of the organism declines, and population is more vulnerable to being wiped out by
new diseases or climate changes because of the inbreeding (Alters, 2000).
Conservation biologists recognize that biodiversity can be sustained only if the evolutionary
mechanisms that have given rise to species and communities of organisms continue to operate.
The goal is to preserve individual species and sustain ecosystems where natural selection can
continue to function (Campbell, 2004). The goal of preserving individual species can only be
obtained when a successful habitat fragmentation and subdivided population is achieved. The
determination of a high-quality patch of land, free from predators and with abundant food
sources, allows the reproductive cycle to start and maintain a constant reproduction of
offspring, allowing the area to sustain the species. A habitat where a subpopulation’s
reproductive success exceeds its death rate will allow individuals to disperse to other areas,
often in search for food or places to reproduce. The migration of individuals allows the
biodiversity of a species to be maintained and allows for continued evolution, resulting in
ecosystem
balance.
Sources
of
Genetic
Variation
Genetic variation is the process by which basic mechanism of evolutionary change takes place.
Like the Mendellian patterns, there are recessive and dominant genes, but along side these
inheritance studies are contributing factors such as structure of DNA, transcription of DNA to
mRNA, translation of the mRNA to protein.Basically three areas are responsible for genetic
variation: mutation, gene flow, and sex.(cite Mendellain patterns) Mutation—This is a change in
DNA or the hereditary components of life. Mutations are random, (Lederberg, 1967), and can
be beneficial, neutral, or harmful to F1 as a result of germ line mutations or changes in
reproductive cells during meiosis. Some bacteria are antibiotic resistant, some are not, and
some viruses have genetic coding that allows science to produce immunizing agents for them,
where some like Human Immunodeficiency Virus, HIV, do not. In fact, recent research now
shows the Duffy Antigen Receptor for Chemokines, (DARC), which evolved to protect Africans
against malaria, actually makes them more susceptible to HIV. (Is this from Lederberg, 1967?)
Gene Flow— is also referred to as migration or movement of genes from one population to
another such as cross pollination with plants, or movement of genes from city to city with
people. Gene flow can either be low rates such as plant pollination with limited distance, or
high rate as in viruses carried by insects for several miles. Gene flow can introduce or
reintroduce genes increasing the variation. In addition genes can move across populations
reducing any likelihood of speciation. Sex—Another descriptive word for this is shuffling or the
congregating of genetic material which differentiates outcomes even within similar families. As
haploid cells change to diploid cells resulting in 23 pairs of chromosomes, the meiotic process
then configures the codons in three letter combinations. As this sequencing takes place the
variations of the sequences create numerous changes in the outcome or genetic variation. An
example of this would be trisomy 21 which is the addition of a chromosome causing Down
syndrome
in
humans.
Conclusion
Ignoring the concept of natural selection would be unwise. The planet is constantly
evolving and with biological diversity the descendants of survivors are able to adapt whether
through mutation or variation and filling the gaps left those who are now extinct. The history of
natural selection provides numerous examples that validate this process and there are those
being
discovered even now. The theory of natural selection is one of the most important biological
findings
and
should
receive
the
acceptance
it
deserves.
References
Alters, Sandra, 2004, Biology Understanding Life, 3e, Jones and Bartlett Publishers Sudbury,
Massachusetts
Campbell, N.A., Reece, J.B., Simon, E.J., 2007, Essential Biology with Physiology, 2e,
Pearson
Education,
Inc.
San
Francisco,
CA
Campbell, N.A., Reece, J.B., Simon, E.J., 2004, Essential Biology with Physiology, 1e,
Pearson
DARC,
Education,
2008,
Inc.
retrieved
San
August
8,
Francisco,
CA
2008
from;
http://www.sciencedaily.com/releases/2008/07/080716121355.htm
Lederberg, J. 1967. Lederberg Replies. Bulletin of the Atomic Scientists, June, Vol. 23 Issue 6,
pp. 60-61.