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Table 1 A summary of the main mechanisms of evolutionary change. Mechanisms are listed in the order presented in the activity (Futuyma 1998; Morris et al. 2013)

From: Making evolution stick: using sticky notes to teach the mechanisms of evolutionary change

Mechanism Description
Founder effect An event that occurs when a fraction of the members of a population leave the main population to form a secondary population. Just as in bottlenecks, allele frequency in the colony may differ from the main population, but this is due to colonization and not catastrophe. Can be a specialized instance of genetic drift
Gene flow The transfer of alleles between populations, usually through migration of an individual or its gametes. Gene flow is one of the main mechanisms, in addition to mutation, and recombination, that can introduce new genetic variants to a population
Genetic drift Random fluctuations in allele frequency, due to chance or random sampling; its effects are more obvious in smaller populations.
Natural selection Occurs when individuals with a heritable trait have higher fitness (via increased survival and/or offspring number) than individuals without the trait. Individuals with the trait then pass their alleles to their offspring. This is a non-random process. Over generational time, selection can create populations that have adapted to succeed in specific environments
Population bottleneck An event in which a population’s size is severely reduced, e.g., by a natural disaster like volcanic eruption or disease like the Black Plague. Allele frequencies in the surviving population may differ from those in the original population, and some alleles might be missing altogether
Sexual selection (only covered in homework) A specific instance of natural selection. Evolution by sexual selection occurs when individuals with a heritable trait are more successful at getting mates and producing offspring than individuals without the trait
Mutation (not addressed in activity) Refers to changes in an individual’s genome. Provides the ultimate and original source of genetic variation for a species or population. Not all mutations have consequences for an individual (neutral mutations), but those that do can be harmful or beneficial. Must occur in the gametes of an organism to be a mechanism for evolution (i.e., the change must be heritable)