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Microevolution refers to small-scale changes in gene frequencies in a population over a few generations. These changes may be due to several processes: mutation, gene flow[?], genetic drift, as well as natural selection. Population genetics is the branch of biology that provides the mathematical structure for the study of the process of microevolution. Biologists distinguish between microevolution and macroevolution, which refers to large-scale changes in gene frequencies in a population over a long period of time (and may culminate in the evolution of new species).

Typically, observable instances of evolution are examples of microevolution, for example, bacterial strains that have become resistant to antibiotics. Because microevolution can be observed directly, both pro-evolution and anti-evolution groups agree that it is a fact of life.

Most biologists consider the difference between microevolution and macroevolution to be relative. Creationists who reject Darwin's theory of evolution through natural selection argue that the difference is absolute. They have proposed that microevolution always takes the form of destructive genetic mutations, which happen to confer an advantage to individuals in a specific environment. Because macroevolution requires many constructive genetic changes, they argue that microevolution cannot lead to macroevolution. One example of a destructive mutation that conferred a competitive advantage under a specific situation occurred in Streptococcus pneumoniae, some strains of which are resistant to penicillin. But this resistance requires the bacterium to expend extra resources that the nonresistant bacteria do not, and so it does not compete well with them in the absence of penicillin.

More specifically, the contention of creationists is that the observed and verified process of microevolution does not lead to increasingly complex species. When the processes of natural selection and survival of the fittest take place, they lead to the elimination of certain unuseful genetic traits, decreasing the genetic complexity and diversity of the affected species, creationists say. If this claim is valid, proponents of macroevolution must accept that increases in genetic complexity are brought about solely through mutation, which would require this type of mutation to be relatively common. Although helpful mutations have been observed, mutations that increase genetic complexity have not.

See also

Speciation, Molecular evolution, Population genetics

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