Evolution: Mechanisms of Change
Evolution is the change in the heritable characteristics of biological populations over successive generations.
1. Natural Selection
Differential survival and reproduction of individuals due to differences in phenotype. It is a key mechanism of evolution.
2. Genetic Drift
Variation in the relative frequency of different genotypes in a small population, owing to the chance disappearance of particular genes as individuals die or do not reproduce.
| Mechanism | Effect on Genetic Variation | Population Size Dependence |
|---|---|---|
| Natural Selection | Decreases (usually) | Low |
| Genetic Drift | Decreases | High (Strongest in small pops) |
| Mutation | Increases | Low |
| Gene Flow | Increases (within population) | Low |
Common Mistakes
"Evolution is just a theory." In scientific terminology, a theory is a well-substantiated explanation of some aspect of the natural world, based on a body of facts that have been repeatedly confirmed through observation and experiment.