The Four forces of Evolution
Evolution is divided into two categories macroevolution and microevolution; macroevolution focuses on the formation of a new species, while microevolution focuses on the change in allele frequencies in a population (47). The process of evolution has four forces, mutation, gene flow, genetic drift, and natural selection. Evolution is caused by the isolation of populations which leads to variation and eventually speciation. A population is a group of individuals within which breeding takes place. A species is a group of populations that is capable of interbreeding and producing fertile offspring. Variation can occur at two levels; with in a population and within a species. Variation can also occur between populations. Variation is a change in the alleles or allele frequency of a population, caused by isolation mechanisms (47). When a population is separated and cannot interbreed it will lead to the appearance of a new species, this is an isolation mechanism. Isolation mechanisms prevent gene flow between populations causing random mutation to effect the only the original population. This leads to a speciation, or the formation of a new species. If two populations remained separated for a significant amount of time they will no longer recognize each other mate choices; this is when a new species is formed. There are two types of speciation that occur between populations or in the creation of a new species. The first is cladogenesis when two populations come to differ from each other; the second is anagenesis when one population has been separated from other populations of its species (47). Mutation is the ultimate source of evolutionary change. Mutation constantly introduces new genetic variation (42). The word mutation has a negative connotation, but when considered as an evolutionary force mutation is positive. Mutation is the beginning of variation, if mutation never occurred, nothing would ever evolve or change. When...
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