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Modes of Speciation

Author(s): Tadzia GrandPre, PhD, Nancy Moreno, PhD, and Lisa Marie Meffert, PhD

Processes Driving Divergence

Genetic distinctiveness arises through processes that introduce new alleles and genes into a population (mutation and migration) and processes that alter the frequencies of genes that already exist within a population (natural selection, sexual selection, and genetic drift).

A mutation is a random change in an organism's genetic material. Heritable mutations (those that are carried by the gametes) can introduce new alleles and genes into a population and, therefore, provide raw material for the evolutionary process.

Migration, or the movement of organisms from one place to another, can also cause changes in the gene pools of different populations. Through migration, new alleles can be introduced or taken away from a population, or the frequencies of alleles and genotypes in a population can be altered.

Through natural selection, heritable traits (and the alleles that confer those traits) that are beneficial to reproductive success become more common in a population while those that are disadvantageous become increasingly rare.

Sexual selection is a special form of selection that leads to the development of sexual dimorphic traits (traits that differ between the sexes). Through sexual selection, alleles that confer an advantage in the ability to obtain mates become more common in a population.

Genetic drift refers to changes in a population's allele frequencies that occur due to chance. In general, the smaller the population, the greater the impact of genetic drift.  

These processes, which drive evolution and speciation, can be reviewed in the presentation entitled "Evolutionary Theory." In addition, information about different species concepts, as well as mechanisms of reproductive isolation, can be found in the presentation "Species Concepts and Reproductive Isolating Barriers."