A Background on evolution
Evolution is defined as, "the process by which different kinds of living organisms are thought to have developed and diversified from earlier forms during the history of the earth." The idea of evolution was originally proposed by ancient Greek scholars, but was quickly rejected in Europe because it conflicted with the teachings of the Bible. Much later, Jean- Baptise Lamarck, a French naturalist, proposed the idea that organisms became transformed by their efforts to adapt to the demand of their environment, but he was unable to put a name for this process. Charles Lyell proved that geological deposits were the product of slow processes over a long period of time, essentially showing that the Earth was old. [1] Both mens ideas helped Charles Darwin form very important theories that led to a general acceptance of the idea known as "evolution," but especially his theories on natural selection. Darwin's theory of evolution, with some modifications, has become the unifying concept of modern biology.
allele frequency changes:
mutation, migration, genetic drift, And natural selection
Evolution occurs as a result of a change in allele frequency. Allele frequency is the proportion of a particular allele to all other alleles being considered, so when there is an increase of an allele, the proportion changes, changing the allele frequency. Allele frequency can change in four different ways:
mutation:
Sometimes, things don't always go according to plan- or in this case, according to sequence. A mutation is a change in the DNA sequence- meaning one of the ATCG bases in the unique sequence of DNA is changed into another base. While this may seem like an unimportant, minuscule change, a change in the DNA sequence will mean a change in the RNA message, codons, the amino acids and finally the proteins that are made up of these amino acids. This alters the allele completely, and in fact, mutation is the only way in which new alleles are created.
There are two causes of mutation. The first and most common is that DNA fails to copy accurately, as shown to the right. These mutations are known as "naturally occurring." The second cause is that an external influence can cause a mutation. Specific chemicals or radiation waves will cause DNA to break down, and when the cell repairs the DNA, it might make a mistake. So the cell would end up with slightly different DNA and therefore a mutation. |
Migration
In Migration (also known as gene flow), a group of individuals move from one population to another. Similar to genetic drift, migration will often occur randomly. If individuals from the migrant population breed with those of the new population, the alleles between the two will be exchanged. Gene flow increases the diversity of the gene pool (which is all of the alleles in an interbreeding population)
|
genetic drift
Genetic Drift is in essence a random change in allele frequency. Genetic Drift is important for small populations, where random events can have an impact on the allele frequencies. Evolution by genetic drift is not adaptive, but aimless, because it is by chance alone that the alleles change. Genetic drift is common in two main population events: the founder effect and population bottlenecks.
In a founder event, a few individuals leave the original population and create a new population (i.e. colonizing an island). Founder effect is often mistaken for migration, but the two are very different: In the founder effect, the few individuals that start the new population will likely have a different allele frequency than the source population. When this new population breeds, it will produce more organisms of the same allele frequency, effectively creating an entirely different population. For a population bottleneck, a population is drastically reduced in number (i.e. an earthquake kills most of the individuals in a population). The disaster is completely random. The surviving members of this disaster will eventually form a new population, but this time it will be dominated by the genetic features present in the surviving members. |
|
natural selection
The most well known form of evolution, Natural Selection is Darwin's most famous theory. In principle, it states that evolutionary change is the process in which organisms that are better adapted to their environment will survive and reproduce. The organisms that do not have the characteristics to help them survive in their environment have a higher chance of not surviving, therefore not producing and not passing on their traits. The phrase "Survival of the Fittest" derives from Darwin's theory.
There are three conditions needed for Natural Selection to occur. The first is a variation is a trait (i.e. some frogs are green and others are brown). The second is that is trait must be heritable, meaning it must be able to be passed down during reproduction. Examples of heritable traits include eye color, bone structure, etc. Learned behaviors cannot be passed down. The third condition is that there must be differential reproductive success. This is the part that was previously described: the idea that organisms more adapted to a given environment will have a greater likelihood of surviving until reproductive eggs and have offspring of their own.
There are three conditions needed for Natural Selection to occur. The first is a variation is a trait (i.e. some frogs are green and others are brown). The second is that is trait must be heritable, meaning it must be able to be passed down during reproduction. Examples of heritable traits include eye color, bone structure, etc. Learned behaviors cannot be passed down. The third condition is that there must be differential reproductive success. This is the part that was previously described: the idea that organisms more adapted to a given environment will have a greater likelihood of surviving until reproductive eggs and have offspring of their own.
There are three types of Natural Selection: Stabilizing, Directional, and Disruptive.
Stabilizing Selection, the most common of the three, is when the population mean stabilizes on a particular trait. This process selects against the extreme phenotypes and as an alternative favors the majority of the population that is well adapted to the environment. An example of this is insect wing size. In many insects, wings are neither to small not to bulky because the environment favors insects of average wing size.
Stabilizing Selection, the most common of the three, is when the population mean stabilizes on a particular trait. This process selects against the extreme phenotypes and as an alternative favors the majority of the population that is well adapted to the environment. An example of this is insect wing size. In many insects, wings are neither to small not to bulky because the environment favors insects of average wing size.
In Directional Selection, one extreme of the trait distribution experiences selection against it, while the other extreme is favored. This results in a shift of the total population's trait distribution towards one extreme. A good example of this is a giraffe: the environment was not well suited for giraffes that had short necks, and as a result, the distribution of neck length began to favor giraffes with long necks.
The third and final type of Natural Selection is Disruptive. This time, the environment is most well suited to those who are the extremes in a population, meaning the organisms that lie in the middle of the trait distribution will be negatively affected.
evidence of evolution
Ever since Darwin's time, people have been looking for evidence that points towards the validity of the new, strange idea known as "evolution," Today, the modern world has quite a few pieces of evidence that prove Darwin's theory. Ancient organism remains, similarities among living organisms, and fossil layers are some of the main pieces of evidence. The work being done on finding evolutionary evidence continues to this day. Humans are still discovering fossils buried for thousand of years, scientists still analyzing similarities in DNA.
There are three major forms of proof that we have of evolution. The first is homologous structures: organisms that share a common ancestor have similar structure, most clearly seen through bone structures. The second is known as convergent evolution, which shows that unrelated species will evolve similar structures if the environments they live in have similar conditions. Finally, there is embryology: by comparing the embryos of different species, scientists can identify which shared a common ancestor.
There are three major forms of proof that we have of evolution. The first is homologous structures: organisms that share a common ancestor have similar structure, most clearly seen through bone structures. The second is known as convergent evolution, which shows that unrelated species will evolve similar structures if the environments they live in have similar conditions. Finally, there is embryology: by comparing the embryos of different species, scientists can identify which shared a common ancestor.
The evolution of the thorny oyster
The Thorny Oystern pertains to the phylum Mollusca, and so they evolution of the mollusks is also the evolution of the Spondylus Americanus. Mollusks occur in almost every habitat on Earth. The Mollusca include some of the oldest metazoans known. Ancient Precambrian rocks contain bilaterally symmetrical, benthic animals with a univalved shell that resembles those of mollusks. This means that the ancient mollusks must have evolved a bivalve shell over time. [2]
Being a sessile animal, the Atlantic Thorny Oyster had no way to defend itself. Its spikes on its shell were originally thought to deter predators, but in fact it attracts other organisms. Other sea creatures will settle on the shell. These organisms are known as epibionts, and use the spike on the oyster's shell as a shelf to rest on. This oyster uses the concealment affect of epifauna, which conceals it from other predators completely.
Being a sessile animal, the Atlantic Thorny Oyster had no way to defend itself. Its spikes on its shell were originally thought to deter predators, but in fact it attracts other organisms. Other sea creatures will settle on the shell. These organisms are known as epibionts, and use the spike on the oyster's shell as a shelf to rest on. This oyster uses the concealment affect of epifauna, which conceals it from other predators completely.