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Other Mechanisms of Evolution KEY CONCEPT Natural selection is not the only mechanism through which populations evolve. Other Mechanisms of Evolution Gene flow • Definition: Movement of alleles from one population to another • How it works: When animals move from one population to another & breed in the new population; when spores or seeds of plants or fungi are spread to new areas bald eagle migration Other Mechanisms of Evolution Gene flow: • Lots of gene flow between populations Results in • Lots of gene flow Results in between populations Similar populations (genetically) Different populations (genetically) that could evolve into different species Other Mechanisms of Evolution Genetic drift • Definition: Changes in allele frequencies due to chance alone • How it works: Small populations are more likely to be affected by chance; Due to chance some alleles may increase in frequency while others may decrease & even become eliminated from the population Other Mechanisms of Evolution Genetic drift • Key Terms – Bottleneck effect: Genetic drift that occurs after an event drastically reduces the size of a population – Founder effect: Genetic drift that occurs after a small number of individuals colonize a new area • Negative effects: Population loses genetic variation, so population is less likely to have some individuals that will be able to adapt to a changing environment; harmful alleles may become more common due to chance alone Other Mechanisms of Evolution Sexual selection • Definition: Process in which certain traits increase mating success & therefore become more common in the population. • How it works: Females preferentially mate with males that display certain traits, so those traits get passed onto offspring & can become more exaggerated each generation Other Mechanisms of Evolution Sexual selection • Types – Intrasexual: Competition/fighting among males for females – Intersexual: Males display certain traits to attract females