The core mechanism of evolution is the change in allele frequencies in populations over generations due to the combined effects of several processes. The most central mechanism often highlighted is natural selection, but evolution also proceeds through mutation, genetic drift, gene flow (migration), and non-random mating. Together, these forces alter genetic variation and shape how populations adapt over time. Key mechanisms
- Natural selection
- Differential survival and reproduction among individuals based on heritable traits.
- Traits that confer a reproductive advantage increase in frequency in the next generation.
- Over many generations, populations become better adapted to their environment.
- Mutation
- Generates new genetic variation by altering DNA sequences.
- Most mutations are neutral or deleterious, but some can be beneficial.
- Mutations provide the raw material for evolution and are the ultimate source of new alleles.
- Genetic drift
- Random fluctuations in allele frequencies, especially in small populations.
- Can lead to the fixation or loss of alleles regardless of their impact on fitness.
- Includes founder effects and population bottlenecks.
- Gene flow (migration)
- Movement of individuals or gametes between populations.
- Introduces new alleles and can homogenize differences between populations.
- Can counteract divergence caused by local adaptation.
- Non-random mating
- Mating preferences or assortative mating influence which alleles are transmitted to offspring.
- Changes in genotype frequencies can occur without altering allele frequencies, but over time, can impact evolution when coupled with selection.
How these interact
- Mutations create variation; natural selection, drift, and migration change frequencies of that variation.
- In large populations, selection and gene flow often dominate long-term adaptation, while drift is more influential in small populations.
- The interplay among these forces explains patterns such as adaptation to environments, speciation, and genetic differentiation among populations.
If you’d like, this can be expanded into concrete examples (e.g., antibiotic resistance in bacteria, beak shape in Galápagos finches, or fruit fly eye- color mutations) or visual aids to illustrate how allele frequencies shift under each mechanism.
