Other Forces of Evolution
Evolution Is Not Only Selection
Genetic drift
Genetic drift is random change in allele frequencies. It is especially important in small populations, where chance events can have large effects.
Gene flow
Gene flow occurs when individuals move between populations and bring alleles with them. It tends to make populations more similar.
Non-random mating and selection
Mate choice and mating patterns can also change which alleles are passed on. Natural selection is not the only force shaping evolution.
Major evolutionary forces
Natural selection
- Non-random
- Depends on trait differences in reproduction
- Can produce adaptation
Genetic drift
- Random
- Stronger in small populations
- Can fix or lose alleles by chance
Small populations matter
In small populations, chance can outweigh selection more easily, so drift can strongly affect evolution.
Which evolutionary force is random?
Genetic drift changes allele frequencies by chance.
Correct answer: Genetic drift
What is gene flow?
Gene flow brings genetic variation into or out of populations.
Correct answer: The movement of alleles between populations through migration and reproduction.
Why is drift especially important in small populations?
Random sampling effects are stronger when fewer individuals are involved.
Correct answer: Chance has larger effects