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Microevolution is the change in allele frequencies that occurs over time within a population. [1] This change is due to four different processes: mutation , selection ( natural and artificial ), gene flow and genetic drift .
Evolution causes organisms to adapt to their local environment; when the environment changes, the direction of the trend may change. The question of whether there is evolutionary progress is better formulated as the question of whether there are any largest-scale trends in evolution (McShea, 1998).
Macroevolution refers to evolution that occurs at or above the level of species, in particular speciation and extinction, whereas microevolution refers to smaller evolutionary changes within a species or population, in particular shifts in allele frequency and adaptation. [135] Macroevolution is the outcome of long periods of microevolution. [136]
[24] [5] [25] [26] [16] [10] [27] Within microevolution, the evolutionary process of changing heritable characteristics (e.g. changes in allele frequencies) is described by population genetics, with mechanisms such as mutation, natural selection, and genetic drift. However, the scope of evolution can be expanded to higher scales where different ...
Natural selection will only cause evolution if there is enough genetic variation in a population. Before the discovery of Mendelian genetics, one common hypothesis was blending inheritance. But with blending inheritance, genetic variance would be rapidly lost, making evolution by natural or sexual selection implausible.
The word phyletic derives from the Greek φυλετικός phūletikos, which conveys the meaning of a line of descent. [2] Phyletic gradualism contrasts with the theory of punctuated equilibrium, which proposes that most evolution occurs isolated in rare episodes of rapid evolution, when a single species splits into two distinct species, followed by a long period of stasis or non-change.
HIV drug resistance occurs when microevolution causes virions to become tolerant to antiretroviral treatments (ART). ART can be used to successfully manage HIV infection, but a number of factors can contribute to the virus mutating and becoming resistant.
Clostridioides difficile, gram-positive bacteria species that inhabits the gut of mammals, exemplifies one type of bacteria that is a major cause of death by nosocomial infections. [ 3 ] When symbiotic gut flora populations are disrupted (e.g., by antibiotics ), one becomes more vulnerable to pathogens.