The Processes of Evolution

free essayThe theory of evolution plays an important role in the study of the history of life. It has become a unifying theory that serves as a foundation for the whole study of biology. Evolution implies general, well-ordered, consistent and gradual development. This paper discusses the main elementary evolutionary processes: variation, mutation, gene flow, genetic drift, isolating mechanisms, and finally speciation.

Before proceeding with the analysis of fundamental factors that determine changes in the gene pool of species, it is necessary to describe the basic structural units of the evolutionary process, namely, a species and its population. Each biological species is a collection of individuals, similar in basic morphological and functional features, karyotype and behavior. Species interbreed in nature only among themselves, and at the same time producing fertile offspring (Haviland, Prins, Walrath, & McBride, 2013, p. 47). Moreover, representatives of the same species settle unevenly. As a result, they create separate groups called populations. According to Haviland et al. (2013), the latter are members of the same species interbreeding freely and living in a particular area (p. 42-43). Each population is to some extent isolated from others within the same species. In nature, there are no ideal conditions and there are no ideal populations. From the evolutionary and genetic point of view, they can be considered as the basic unit of the evolutionary process. Furthermore, sustained changes in their features, especially in a gene or a set of genes, are an elementary evolutionary phenomenon called variation. Therefore, by selecting one needed trait, there is a possibility of occurrence of other, sometimes undesirable traits in the offspring, correlatively associated with it (Haviland, 2013, p. 42-44). Variability directly affects four forces of evolution: mutation, gene flow, genetic drift, and natural selection.

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According to Haviland et al. (2013), mutation is a stable and non-directional change in the genome. It can be present during an infinitely long time in a number of generations. The value of mutations in evolution is great since thanks to them, there are new versions of genes. They can either lead to a change in characteristics of organisms or not. The earlier a particular mutation happens in the body, the greater impact it can have on the development of the organism (Haviland et al., 2013, p. 42).

In addition, an important source of variability is a gene flow being an exchange of genes among populations of the same species because of interbreeding of their representatives. According to Haviland et al. (2013), some migrant individuals of one population get to another, and new genes appear in the gene pool of the latter. During such breeding, progeny genotypes will be different from the ones of both parents, and, thus, the gene pool of the population is changed (Haviland et al., 2013, p. 44).

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Since the renewal of the population size occurs due to a small number of its representatives that have not the whole set of alleles, the new and the original populations will have an unequal genetic structure. A variation in the gene frequency under the influence of random factors is called a genetic drift. It also takes place during the settlement of the population in new areas, because an extremely limited number of members of the given species, which can give rise to a new population, can get to them. Often new homozygous forms segregate as a result of a genetic drift, which can be adaptively valuable and will be further taken up by natural selection (Haviland et al., 2013, p.44-46).

Natural selection is a major factor influencing the evolution of organisms. According to Haviland et al. (2013), its principle function is to eliminate representatives of the population with unfortunate genetic combinations and to preserve genotypes that do not hinder adaptive processes. The process of natural selection is determined by the fact that only those organisms survive and leave offspring that are better adapted to environmental changes than others are. It ensures the adaptation of living organisms to constantly changing environmental conditions (Haviland et al., 2013, p. 44-49). From generation to generation, all living organisms pass a severe test checking the smallest details of their structure and functioning of all their systems in a variety of conditions. This check is a struggle for existence. Only those that have survived are selected and give rise to the next generation.

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Any changes in the genetic structure of the population should be fixed, and this occurs due to isolation. According to Haviland et al. (2013), the latter is any barriers (geographical, ecological, behavioral, reproductive and others) that complicate and make impossible the crossbreeding of individuals from different populations. Although isolation itself does not create new forms, it nevertheless retains genetic differences among populations that are exposed to natural selection. Its importance in the evolution process is that it strengthens and consolidates the initial stages of genotypic differentiation. Isolation increases the effects of factors that determine evolutionary changes; its impact on the population is not directed (Haviland et al., 2013, p. 47). A change in the genotypic composition of the population is a leading starting mechanism of the evolutionary process.

According to modern views, all major processes of evolution occur within species, or on the micro evolutionary level. Microevolution culminates in speciation or the occurrence of species that are reproductively isolated from the source and other related species. Therefore, there are no fundamental differences between microevolution and macroevolution. They have a gradual, divergent and long-term nature with the last stage of speciation. Species consists of many sub-species and populations, being a genetically integrated and closed system (Haviland et al., 2013, p. 47-48).

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Thus, evolution requires factors that lead to evolutionary changes in the population. This role is fulfilled by the mutation process, variability, gene flow, and genetic drift. Having different nature, they act randomly and non-directionally, creating different genotypes. Factors that ensure the emergence of barriers to breeding are of great importance for evolution. These are various forms of isolation, which fix any differences in genotypes of different populations. Finally, natural selection, a factor guiding the evolutionary process, is necessary for the existence of strong and healthy representatives of a species. All these forces affect the population and give rise to the elementary evolutionary phenomenon.