This small essay about Evolution may be of some use to you. I still had it lying around and thought it's better of sharing than only having my professor read it. Might start up a conversation as I probably missed a lot; and maybe made some 'wrong' statements.
EvolutionIn 1820 Charles Robert Darwin (1809-1882) was studying biology. Back then the common view on how species had come to be, was that God had created them in 24 hours. Special Creation, this theory was called. This theory was based on three statements and the first one was that people believed that all creatures had been formed independent of each other. This 'creation' happen about 6000 years ago and organisms hadn't changed since.
Darwin at first, but after that his colleagues, have managed to define a new theory, called Evolution. All three statements for the theory of 'Special Creation' can now be easily explained as being wrong. In this essay I'll try to explain why Evolution is a good explanation for how organism became this way and why there are different species.
Organisms have been around for about 3.8 billion years, this has been discovered by geologists. They noticed that a lot of rocks on the surface had recognizable structures. They could find wave-like shapes on hard rocks just like they could see them on a beach, and they could find rocks with 'mud-cracks' just like they saw them in dried up river beds. This led them to think that processes we can see today also shaped the earth in the past. They realized that this could give them an estimate of how old Earth could be, because they could calculate how much sediment a beach collected in a year. By mapping rocks from all over the world and calculating how much time it would take to form those rocks, it became reasonable that the Earth had been here longer than 6,000 years.
Through time fossils were found, in very old rock layers, that made scientists believe that animals and plants had been living on earth for more than 3 billion years. Later through the discovery of radiometric (where through the half-lives of certain elements age of fossils can be calculated) this number was set on 3.8 billion years ago.
It is also through fossils that scientists came with the idea that species haven't been the same through time. Biologists discovered organisms in fossils that looked nothing like species living today. Some of these animals would have been so big that it would be impossible to not have discovered them. This led to the theory that some organisms had become extinct. And that they had looked different in the past. Species must have changed and some had gone extinct.
Also certain vestigial structures were discovered. Organs or bones that seemed to have no purpose, but were actually left-over after evolving from other species.
For example whales seem to have certain bones that can clearly be recognized as a hind-leg bone structure, which is still there from when land mammals evolved into see mammals (like whales are). Also in humans the tailbone doesn't have any purpose anymore but could be recognized as left-overs from the tailbones of primates. By tracking these vestigial traits a long way back
But even in living species this 'change' could be discovered. Through experiments with fast producing species (like insects) scientist discovered that when the environment changed the species lived in, the species itself would change as well. The adaptations always seemed to give the organisms and advantage. This led to the theory of 'natural selection'.
Natural selection works in a way that the 'fittest' in a species produces more offspring and thus causes genes from this individual to spread relatively more in the population. This all depends on mutations in the DNA of an individual, causing the genotype of a population to vary. Certain mutation cause an individual to have an advantage in finding food, reproduction, strength, etc, and thus getting more offspring with the same genes. The process of adaptation doesn’t really effect individuals but causes the entire population to adapt over several generations.
Through the analysis of bone-structures, scientist have discovered that all species have evolved from one common ancestor. This became clear when biologists recognized certain homologies in organisms. Homologies are organs/bones that have the same structure as other organisms have but a different purpose. These organs have been left over from the species' ancestors while evolution occurred. For example; a mole, human, horse and dolphin all seem to have the same sequence and arrangement of bones, but in different proportions. From this we can conclude that these mammals all share the same ancestor, but all have evolved and specialized in different ways.
Another way of detecting similarities between totally different species is studying embryo's of that species. In the first stages of development, most mammal embryo's seem to have almost the same shape. Later on in the development difference become clear and species can be recognized.
Off course with the arrival awareness and understanding of DNA, more evidence for the 'common-ancestor' theory came to light. As in homologies, molecular homologies also work by the principle that traits from the ancestor stays imbedded in the genes off the offspring. Only now this can be discover on a molecular level. Certain pseudogens have the ability to be moved through the DNA sequence and placed in a new location. These processed psuedogens are transcribed into RNA and later reverse transcripted back into the DNA in a new location. Because these psuedogens don't have a introns, the don't show in the genotype of the organism, and thus are left in the DNA sequence for many generations and through many evolutional stages. Tracking these processed psuedotypes gives us an idea of what species evolved from which ancestors.
The only question left now is; how did this first organism look like and how did it evolve from non living minerals. Scientist still don't have a perfect answer, but reliable experiments have pointed out that simple RNA sequences would have been able to evolve and reproduce them selves. And as the ability to evolve is the most important definition of life, this seems to be a good answer. But where did these first RNA life forms come from? Some say that a comet struck Earth and carried simple organic compounds. This has been proven to be possible as a couple of comets carrying significant concentrations of glycine, alanine, glutamine acid, voline and proline struck Australia in 1969. Another theory is based on research done by a graduate student of the University of Chicago, Stanley Miller. He discovered that when exposing the right components to a simple electrical spark (like lightning) certain organic molecules can be formed. Later scientist stated that the components used for this experiment were unlikely to be found in Earths atmosphere more than 3 billion years ago. The final questions in Evolution has not been answered yet, but theories for the creation of life on earth are developing rapidly.
