Evolution by Natural Selection
How Populations Change
Mechanisms of evolution
Evolution is a change in allele frequencies in populations over time. Natural selection is one mechanism, but mutation, gene flow, genetic drift, and nonrandom mating also contribute.
Selection requires variation
Natural selection can only act on heritable variation that affects survival or reproduction.
Fitness and adaptation
Fitness in biology means reproductive success, not physical strength. Adaptations are traits that increase fitness in a specific environment.
Which statement best describes natural selection?
Natural selection acts on heritable differences, changing allele frequencies across generations.
Correct answer: Populations change because heritable traits affecting reproduction become more common
Why is genetic drift stronger in small populations?
Sampling error is greater in small populations, so alleles can be lost or fixed by chance.
Correct answer: Random chance has a larger effect on allele frequencies when population size is small.
Selection and drift
Natural selection
- Nonrandom
- Driven by fitness differences
- Produces adaptation
Genetic drift
- Random
- Strongest in small populations
- Can reduce variation without adaptation
Fitness in evolutionary biology refers to:
Fitness is measured by contribution of genes to future generations.
Correct answer: Reproductive success