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Evolution is an idea that was studied and researched by Charles Darwin and Alfred Wallace is 1858. They studied the idea that certain inherited traits change over time. Many of these genes and traits change due to mutations, genetic recombination, and gene flow. The idea of evolution has furthered biology and has become an essential field of study when studying biology. Darwin has spent many years researching and collecting facts for his theory and it hass affected many scientists past and present.
Many people are skeptical of evolution because people have said that it is "just a theory". Many of those people do not understand what a theory actually is. A theory, as stated by Webster dictionary, is "the analysis of a set of facts in their relation to one another." Evolution is a theory, but it is backed up and supported by many different facts. A theory is always supported by different facts coming together and they are made to interpret facts and different data that scientists collect. In order to creat a strong scientific theory, one has to support, his or her theory, with man facts and observations. These facts and observasions help other scientist research the theory and eventually prove it is true.
When Darwin wrote The Origin of Species, he used four main lines of evidence in order to support his claims. His first line of evidence was biogeography, the study of what the geographical distribution of different creatures was. He looked at where each specie lived and what they were there. Darwin believed that as species moved and colonized, boundaries were created between different species, however they all managed to stay in the same region. Animals with roughly the same body plan tended to be found on the same continent or in the same general area. That is why scientists tend to find beavers and muskrats living in the wetlands; they are two similar species that are living in the same region. Darwin also found many different species of zebras living in Africa, all similar enough to be related in some way. South America was in habited by viscachas and agoutis, which were two small, closely related rodent-like animals that live within the same geographic area. Darwin believed that similar species are found in nearby areas due to common ancestry. The parent species near the offspring, this shows that the similarities in traits was due to decent with modification. The idea of biogeography is that many closely related species would live in the same region, and this was one of Darwin's major lines of evidence.
Another line of evidence Darwin used was paleontology. Through paleontology, Darwin examined the fossil records of extinct species. What he found was very similarly related fossils of closely related species. He understood that the closer to the earth's surface a fossil was, the later that organisim had died. He used this as a guide to figure out at about which time all of these species had lived. What Darwin also found was that closely related species' fossils tended to lie closer to one another . As one species would die out, another one would be founder closer to the earth's surface. Scientists have figured out that a horse like creature called a Hyracotherium was succeeded by an Orohippus. The Orohippus was eventually succeeded by Epihippus and then the Mesohippus, which was eventually succeeded by many other horse like creatures. These not only stayed in North America, but also moved to China and made their way through Asia and Europe. After five million years they had almost all died away, leaving behind the Dinohippus, which then led to the Equus, the modern day horse. Darwin's study of paleontology led him to understand the different periods of time that each animal had lived in and helped uncover which species were connected through ancestry.
Darwin's third line of evidence was embryology. Here Darwin looked at and studied the similarities between the different embryos of certain animals. He observed that certain species of animal's embryos pass through the same stages of life as other distinct species' embryos. For instance the embryo of a mammal passed through stages similar to the embryo of a reptile. Darwin believed that "the embryo is the animal in a less modified state." This meant that by looking at an animal's embryo, one could see more similarities between apparently different adult animals. He also suppourted this line of evidence by reporting, that the larvae of flies, moths, and beetles are very similar to one another, even though their adult forms like drasticly diffrent. The study of an animal's embryo has led to the discovery of many previously unknown connections between animals.
Darwin's fourth and final line of evidence was morphology. In the study of morphology, Darwin studied the shape and design of certain creatures. Darwin grouped the different species and was able to study how each creature was classified by putting them into larger categories. He studied all the birds together, all the fish together, and sorted the lions and tigers with all cats. By doing this, he was not only able to study what made each of these creatures so unique, but firgure out why all of them belonged in a particular seperate category.To illustrate the grouping system, he observed that all vertebrate had backbones and all mammals had fur and mammary glands. He also examined that some mammals, like kangaroos, which had pouches in which they nursed their young. Once modern science came into play, molecular evidence could also be used to support evolution. Today we are able to examine the DNA and the RNA of many different animals and plants, allowing us to make many different conclusions of why different animals are related.
Evolution there are two different levels, micro and macroevolution. Microevolution usually happens at a much smaller scale then macroevolution,within a single population of creatures. Macroevolution goes beyond the boundary of single species and is used to observe changes from ancestral species to a new species. Microevolution views the changes that occur within the gene pool of a certain population over time. Microevolution tends to create small changes in certain populations over time while macroevolution tends to deal with much large changes to a population. Macroevolution can create large changes, such as animals being able to fly, but it tends to take a much longer time then microevolution.
In the microevolution process, many of the changes that occur on that level are usually as a result of genes. These change between reproduction cycles, allowing certain organisms to have varying characteristics due to a mixture of genes. These genes are then tested by natural selection. Natural selection is the idea that animals with a certain gene can die out because they are not able to fit into their environment. If certain animals have an unfavorable trait, there is a smaller chance that they will be able to survive and reproduce fertile offspring. For example An animal that blends into its surroundings will be able to escape predators better in a forest than one that stands out. An animal that stands out would die over time. Natural selection can cause unfavorable genes in a certain environment to die out. Natural selection can impact a population in three different ways. First natural selection can stabilize a population. Stabilizing selection normally would act on an environment with a very high biological diversity. When stabilizing selection occurs, the enviorment does not favor the extremes of the population and favors the heterozygous. The extreme values are selected against while the mean values are left alone. This would cause the extremes to decrease and the medium to remain unchanged, keeping the phenotype bell curve consistent. Another mode of selection is directional selection. This form of selection occurs when the environment favors one extreme trait over another. This means that the distribution of one gene in an environment become, less adaptive as the environmental change takes place. That gene would not be favored in the enviorment causing its frequency to decrease. The population would move towards the mean and the extreme that has a better chance of serving in the environment. Directional selection is able to cause small evolutionary changes in species over time. When directional selection takes place, it results in a decrease in bio-diversity. The final mode of slection is disruptive selection. This occurs when the median of a certain population is targeted and the extremes have a higher chance of surviving in a certain population. If gene flow in the population becomes restricted, then the population can evolve into two different species. Natural selection has a large impact on the adaptive microevolution of a population.
The genes of certain organisms can also change due to a mutation that that organism will bring into an environment. If a creature with a mutation enters the environment, it will pass on its gene to the population as long as reproduction occurs. Once that gene is in the population, it will be able to mix in the gene pool, creating new variation in a certain population.
Genetic drift is the change in frequency of a gene, the number of that genes in a population compared to the number of genes in the entire gene population, in a population due to random sampling and chance. The alleles of offspring are determined by the allelsof the parents. Chance has always had a role in determining the different genes of a species' gene pool due to the diffren combinations in offspring.
Gene flow is the exchange of alleles from one population to another one. The genes are usually transferred between the same species. Transfers between two organisms could result in the form of a hybrid. When organisms migrate in-between different populations they can increase the gene frequency and can even introduce genetic variation into the population. Many different factors affect the rate of gene flow in a population. One factor is mobility; the more mobile a population is the higher chance that different organisms will migrate into their population. This would allow for an increase in the gene frequency. The higher the mobility the more likely an organism is to migrate. In genetic drift there are two diffrent effects that can happen on the population. The first one is the bottleneck effect, this is when population is significantly decreased do to a random event caused by the enviorment. In a bottleneck effect no allel has an advantage in survival over another allel. This would cause a very large drop in genetic frequency. Due to the lack of allel frequency in many of the recesive allels this can lead to a loss in genetic variation. Another effect that can happen is the founder effect. This happens when a small part of a population moves away and forms a new one. The allels that are in the new population usually do not share the same frequency as in the orginal population. This will lead the founders of the new population to have a very large effect on the new population. This may cause the two populations to diverge. Gene flow is important, because it helps scientists understand the transfer of allels between populations.
The Hardy-Weinberg principle states that the allele and genotype frequencies in a certain gene pool will remain the same in each generation as long as five conditions are met. There are certain disturbing influences that cannot interfere or there will be changes in allele frequencies. The first condition is that no mutations should occur, so that no new alleles are brought into the population. The second is that gene flow is cut off. This does not allow migration of alleles into or out of the population. The third is random mating must occur. This means that individuals in the population must pair completely by chance and each male has an equal chance to mate with each female. This is a example of nonrandom mating. The fourth is that no genetic drift occurs. The population is large,because allele frequencies changes due to chance will become insignificant. the fith and final condition is that no natural selection may occur. There should be non selective agent preferences for a certain genotype over another. These conditions are rarely met. Allele frequencies in a population do change from generation to generation. With changes in allele frequency microevolution is occurring in every generation.
Macroevolution is like microevolution, but it is on a large scale. Macroevolution is the study of one species becoming another. A species is a basic unit in biological classification. Species are a group of organisms that naturally meet,breed, and produce fertile offspring. Reproduction isolation is the primary mechanism responsible for seperation of species. Without reproductive isolation, a population would not be able to diverge from another population and form a new species. Reproductive isolation can occur by two different types' of isolating mechanics. One of them is Prezygote mechanics, which acts before fertilization is able to occur within a member of a population. These factors prevent individuals from being able to mate. another factor is geographic isolation, which occurs due to diffrent habitat loacations. Another is temporal isolation, which means that certian members mating seasons do not match up, so they are not able to mate with one another. Mechanical isolation means that reproduction is not able to take place due to the size of the two species genitilia. The last mechanism is gametic incompatibility, which means that the egg is not able to be fertilized by the sperm of another species. The other types of isolation mechanisms are postzygotic mechanisms. Postzygotic mechanisims preven continuation of hybrid offspring lines. It occurs even if fertilization does occur. One type of postzygotic mechanism is zygotic mortality; this means that the zygote is not able to developed, because the egg is not viable. Another type is hybrid sterility; this would mean that the zygote would develop into an adult that is not able to reproduce. One of the many examples of this is a mule, which is the offspring of both a horse and a donkey. Sometimes hybrid offspring experience F2 fitness which would mean that they are able to reproduce but their offspring will not be able to.
One of the main modes of speciation is allopatric speciation. In allopatric speciation, a population will split into two separate geographically isolated populations. Many times this can occur because of a mountain range or a river. The two populations will then be isolated from one another, causing genotypic and phenotypic divergences. Each population will experience different mutations, and diffrent natural slection will occur. Diffrent enviorments will cause each population to evolve in a separate way. Diffrent enviorments will favor diffrent traits. When the populations come back in contact with one another, they will have evolved in such a way that they will not be capable of reproducing; therefore, they will be considered seprate species.
Another mode of speciation is sympatric speciation. This occurs when two separate species come into being while a population still occupies the same location. Two separate species will occur from the same population even though there are no geographical borders between the populations, like there are in allopatric speciation. These species can become so different that they aren't able to interbreed with one another anymore and become two separate species. One common method of sympatric speciation is sexual selection, which causes diffrent traits dispite lack of diffrent enviorments.
The study of evolution has had an impact on biomedical research. It has allowed scientist to examine the parasites of different diseases.By examing the parasites scientists can determine how old certain diseases are. They are also able to figure out how quickly the parasites diversify and bring in different forms of this disease. This helps scientists try to combat it. Malaria is an incredibly dangerous disease that has devastated developing countries around the world. It is estimated that malaria has killed more than one million people and has afflicted more than two hundred and forty-seven million. Using DNA analysis a group of scientists have estimated this disease to be 2.5 million years old. They also figured out that this disease did not affect humans until about 10,000 years ago. The researchers linked the parasites the evolutionary rate of its bird hosts in the West Indies. They were then able to understand the rate at which the parasites diversify in order to spread the disease to other host. This has not done very much in the way of curing malaria, but if we understand the parasites that cause the disease, we have a start to finding a cure.
Evolution has been studied by scientists for many years now. Many of these scientists have made their contributions and discoveries. Darwin has set the stage for many scientists. He has also helped us learn more about the world that we live in and understand more about our enviorment. Darwin has made a great contribution not only to science, but also to average people. He has helped us understand more about the world that we live in.
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