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Evolution- Enjoy reading :)

May 18, 2011

Evolution

Do you believe in evolution? Many people are extremely sensitive about answering that question. Some people are completely against this subject being taught in schools, while others want it to be taught. The truth of the matter is that people don’t realize that evolution isn’t against religion. In fact, evolution is completely compatible with major religions and is accepted throughout the scientific community as being true. In this essay I will discuss evolution’s creation, its microevolutionary mechanisms, its evidence, and my opinion on the subject.

Charles Darwin is believed to be the first person to explain evolution, but it was actually his grandfather Erasmus Darwin who was first to discuss certain aspects of it. Erasmus Darwin realized that competition and sexual selection played a vital role in bringing about changes in species. Erasmus Darwin’s ideas about the change of species were extremely close to those of Jean-Baptiste Lamarch. Like Darwin, Lamarch also formulated a theory about why species were so different.

Jean-Baptiste Lamarch went into much further detail in his analysis of evolution. His theory, which is referred to as “Lamarckism” explained how acquired traits could be inherited. He believed that environments in which organisms lived caused their changes. You could use giraffes as an example. Say we want to find out how the giraffe acquired its long necks. Well, if you were to ask Lamarch, he would say it all had to do with fluida. So here is the situation, the ancestry of the giraffe has a short neck and can only get leaves from short trees. But slowly the short trees are disappearing, so the giraffe is forced to stretch its neck to get leaves from taller trees.  The “fluida” goes to the giraffe’s neck to make it longer. The next generation inherits the little longer neck and the process continues until modern giraffes exist. However, Lamarch was wrong with this theory. Although the environment does have a role in evolution it does not in fact cause for genetic changes within the species. So, the giraffe’s neck didn’t get longer by stretching out to get the leaves on taller trees.

Charles Darwin’s theory of Natural Selection is somewhat similar to Lamarck’s in the way that they both have to do with the environment. However, unlike Lamarck, Darwin theorized that animals respond differently. Darwin said that as environments change, different animals with different traits will either survive or die and that this is what will lead to variation in species over time. As Darwin traveled around the world as the naturalist aboard the H.M.S. Beagle, he observed many animals and fossils that would help support his theory. Both the ideas of Thomas Malthus and Charles Lyell aided and supported Darwin’s theory. Lyell’s theory that the earth was millions of years old gave Darwin’s theory of Natural Selection plenty of time to occur. And Malthus’s theory was that populations reproduce too much, this then leads to lack of food, living space, ect., which then leads to death. Darwin was able to tie this in to his own observations. Lyell’s and Malthus’s ideas along with Darwin’s travels all contributed to his theory on natural selection.

Microevolution refers to small-scale change within populations brought out by mutation, migration, natural selection, and genetic drift. Microevolution is the easiest type of evolution for scientist to study because it can occur in fast reproducing populations. Due to the fast reproducing populations scientists are generally able to study the results within their lifetime. Mutations are heritable changes in DNA that typically give rise to altered gene products. Genetic mutations are rare and often have little effect on the allele frequencies of a population. However, neutral mutations have been accumulating in populations for countless years and have been the source of great genetic diversity among organisms.

Migration is a mechanism of microevolution that leads to gene flow. Gene flow is the flow of alleles due to immigration or emigration. Through emigration alleles leave a population and through immigration alleles enter a population. This flow of alleles tends to counter genetic differences that arise through mutation, natural selection, and genetic drift. So, separated populations tend to stay genetically similar.

Natural selection is the result of the survival or death of members of a population with different traits. There are four types of selection, directional, stabilizing, disruptive, and sexual. Directional selection is when there are already variations within a population, but the number of individuals with a type of variation decrease or increase with the environment as it changes. Stabilizing selection leads to an increase of individuals with an intermediate trait. This is due to conditions that easily kill individuals with either extremes of that trait. Disruptive selection is the opposite of stabilizing selection and leads an increase in either of the extremes. This happens because conditions favor the individuals with the extreme traits over the ones with the individual traits. The last type of selection is sexual selection. This occurs when the males or females of a population tend to exhibit the traits of the organism that attract a mate.

Genetic drift is another mechanism of microevolution. Genetic drift is random changes in allele frequencies over generations. Genetic drift impacts smaller populations much more than larger ones. Genetic drift causes a given trait to become more or less prevalent in a given population. It becomes very prevalent after a severe reduction in population size or when a population is newly established from a few individuals of an old one. Inbreeding is an form of genetic drift because it also leads to a homozygous group.

In science, a theory is a highly probable explanation for something. The Theory of Evolution is a scientific theory and has tons of evidence to support it. This evidence includes biochemistry/DNA, embryology, the fossil record, and comparative morphology.

Biochemistry and DNA are undeniably huge blocks of evidence for evolution. They allow us to find out that humans share 100% of amino acids with chimpanzees. DNA allows us to find out how closely related different species are. DNA comparisons have supported what evolution says it should be every time it has been compared between species.

Like biochemistry and DNA, embryology also provides evidence for evolution. Embryology allows us to see that in the early stages of development birds, fish, and mammals all look exactly the same. This similarity suggests that they all shared a common ancestor and for a period of time develop in similar ways. An example of this is the similarity between infant human and chimpanzee skulls. In the infant stage the skulls are very closely related, which suggest that humans and chimpanzees are related.

Out of everything that supports evolution, fossils might be the most prominent. Fossils helped support Darwin’s theory. In Darwin’s time people generally thought that the earth was only 6,000 years old, but with fossils Darwin was able to prove that it was much older. Fossilization is an extremely slow process that takes ages and the findings of older fossils showed that the earth couldn’t have only been 6,000 years old. Fossils also show evidence of macroevolution. Fossil records show many animals that are in the in-between phase of becoming another species. They show dinosaurs that are in the transition between reptiles and birds. A great example of this is the Archaeopteryx.

The final supporting evidence of evolution comes from comparative morphology. Comparative morphology is the comparison of body forms and structures. Comparative morphology is strong evidence because it shows similarities among animals that have diverged a great amount. It also gives evidence that animals of the same class relate more than animals of different classes. For example, both humans and bears are in the Mammila class and we both have a five-toed/finger structure coming out of the forelimb. So we relate to each other but, if you were to compare the human and the chicken which are in two different classes we don’t share that same characteristic.

So, what is my opinion on evolution? I do believe in it and think that anybody who doesn’t should really research this topic. For me the world-wide acceptance by researchers and scientists of the Theory of Evolution is what convienced me. Also the fact that through biochemistry we are able to prove that humans share 100% of the amino acids with chimps really convinced me. But most of all when I ponder how things became what they are today nothing seems like a better explanation for it than evolution.

Bibliography

Mader, Sylvia S., and Murray Paton. Pendarvis. Biology. Ninth ed. Boston: McGraw-Hill            Higher Education, 2007. Print.

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