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Evolution is a progressive change observed in subsequent generations of a given species. It is through evaluation that historians have found answers to account the differences witnessed in populations that share ample characteristics, yet they cannot interbreed. There are several factors that have been hypothesized to potentiate evolution. Evolutionary, life is believed to have emerged from a single origin, which has undergone speciation to yield different organism in the world. However, it is worth noting that there are other theories, e.g. creation theory explaining the origin of life and differences in the population.
Species refers to a lineage of an organism that are potentially or actively capable of interbreeding in nature. Over thousands of years, these species undergo speciation forming new species. Therefore, speciation is the process where current species undergoes modification prompted by ecological separation, genetic modification or both leading to new species. A group organism of a species living in a given locality at the same time constitutes a population. Isolation of in a population may occur before mating due to ecological, mechanical, behavioral, or temporal factors; or post mating due to gamete incompatibility, zygote mortality, hybrid sterility, or hybrid breakdown (Carey, 2009). Variation result to individuals in a given population possessing different characteristics from those of member species. This may be caused by a number of factors including mutation, genetic drift, natural selection, and introduction of new genes through sex.
Forces of evolution
Changes that can be traced beyond the species level constitute macroevolution while those constricted to a population are regarded as microevolution. For instance, microevolution would involve tracing differences and similarities of a population (e.g. Homo sapiens) while macroevolution would tend to cover evolution tree beyond species level (e.g. from Homo sapiens to mammals). These evolutions would be caused by factors such as natural selection, genetic drift, mutation and migration (gene flow) (Quencez & Bastien, 2011).
Organism ability to survive in their environment will be determined by a number of factors such as differential reproduction, ability of a population to pass heritable traits to the subsequent generation and adaptability. The group within species that will be in a position to compete effectively in the three aspects of selection will dominate the population. Consequently, the population will be defined by the majority leading to evolution. Natural selection takes threes forms; directional where fitness increase with trait value; stabilizing selection, where fitness is concentrated around the mean value; and disruptive selection where fitness is more to the extreme ends of a give trait than at the average level (Carey, 2009). Disruptive selection is believed to result to new species in a community.
Genetic drift, defined as domination of a given allele in a population due to chances, has remarkable contribution to the evolution. In a population with different phenotypes, one allele may be favor by chance, thus result to transmitting its characteristic to the subsequent generation more often the less “lucky” allele. Consequently, a given allele may be faced out, or fixation of the gene occurred leading to evolution.
During reproduction, the gametes undergo a series of divisions (meiosis and mitosis). The cell differentiates to form the various sets of functions of cells in an organism. In the process of division and differentiation, the cell may encounter mutation - a blunder in replication of DNA. This may either be at somatic or germinal levels. Environmental factors such as radiations and chemicals can also lead to mutation (Quencez & Bastien, 2011). The subsequent genes will be transmitted to the subsequent generation triggering speciation and or variation in a population.
Genes flow within and without a population results to variation in a population. New genes introduced in a population by immigrants will result in new characteristic (allele) evolving, in the population (Carey, 2009). Where different populations intermingle, there will be sharing and exchange of allele among them, resulting to marriage of characteristics. Geographical isolation will facilitate the development of characteristic that conform to that environment thus leading to variation between populations.
In conclusion, speciation will lead to variation in a population. Speciation, which depicts evolution, result from interplay or single effect of either mutation, natural selection, gene flow, or genetic drift of a given species.