AP Biology: Natural Selection Practice Questions
Test yourself on AP Biology: Natural Selection with 13 original AP Exams practice questions. Pick an answer to see instant feedback and a full explanation.
Free original practice questions for study purposes. Open Exam Prep is an independent study resource and is not affiliated with, endorsed by, or sponsored by the makers of AP Exams.
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1. A population of beetles includes green and brown individuals. Birds more easily spot green beetles on dark tree bark, and over several generations the brown beetle frequency increases. Which process best explains this change?
Explanation. Brown coloration gives a survival advantage in this environment, and if color is heritable, brown beetles leave more offspring. Natural selection changes allele and trait frequencies across generations; individuals do not adapt by changing inherited traits during their lifetime.
2. Which condition is required for natural selection to cause evolutionary change in a population?
Explanation. Natural selection requires variation, heritability, and differential survival or reproduction. If a trait is not heritable, selection on that trait will not reliably change the next generation.
3. A population of finches experiences a drought that leaves mostly large, hard seeds. Birds with deeper beaks survive and reproduce more than birds with shallow beaks. What type of selection is most likely occurring?
Explanation. Directional selection favors one end of a trait distribution, shifting the population mean. Here, deeper beaks are favored when large, hard seeds dominate.
4. Human birth weight is often used as an example of stabilizing selection because very low and very high birth weights tend to have lower survival than intermediate weights. What happens to the trait distribution under stabilizing selection?
Explanation. Stabilizing selection favors intermediate phenotypes and selects against extremes. This tends to keep the mean similar while reducing variation around that mean.
5. In a habitat with both very light and very dark rocks, medium-colored mice are more visible to predators than either light or dark mice. If coat color is heritable, which pattern is most likely over time?
Explanation. Disruptive selection favors phenotypes at both extremes and selects against intermediate phenotypes. In this scenario, light and dark mice each match part of the environment better than medium-colored mice.
6. A pesticide is applied to a field. A few insects already carry an allele that gives resistance, and these insects survive and reproduce. Which statement best describes the role of the pesticide?
Explanation. Selection acts on existing heritable variation. The pesticide does not create the useful allele in response to need; it increases the reproductive success of insects that already carry resistance.
7. In a large population, genotype AA has an average of 10 surviving offspring, Aa has 8, and aa has 2. Which genotype has the highest fitness in this environment?
Explanation. Fitness is measured by relative reproductive success in a specific environment. AA produces the most surviving offspring on average, so it has the highest fitness among the listed genotypes.
8. A population has two alleles, A and a. Allele A increases survival in cold years but decreases survival in warm years. Which conclusion is best supported?
Explanation. A trait's fitness effect depends on the environment. An allele can be advantageous under one condition and disadvantageous under another, so changing environments can maintain variation.
9. Which observation would provide the strongest evidence that a trait is an adaptation produced by natural selection?
Explanation. An adaptation is a heritable trait that increases fitness in a particular environment. Evidence should connect heritability and increased survival or reproduction, not just the presence of the trait.
10. Why can natural selection act on phenotypes but cause changes in allele frequencies?
Explanation. Selection acts on observable traits that affect fitness. When those traits are partly genetic, individuals with certain alleles leave more offspring, causing allele frequencies to change across generations.
11. A small group of birds colonizes an island. By chance, this founding group has a much higher frequency of a rare allele than the mainland population. Which mechanism best explains the initial difference?
Explanation. The founder effect occurs when a new population is started by a small sample of a larger population. Random sampling can make allele frequencies differ strongly from the source population, even before selection acts.
12. Two populations of the same species live in different environments. Over many generations, different traits become common in each population because different environmental factors affect survival. This is best described as:
Explanation. Divergent selection occurs when different environments favor different phenotypes in separate populations. This can cause populations to become genetically and phenotypically different over time.
13. A student claims, "Natural selection always produces perfect organisms." Which response is most accurate?
Explanation. Natural selection is constrained by existing variation, genetic history, trade-offs, and changing environments. It can increase fitness, but it does not design perfect organisms or plan for future conditions.
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FAQ
What is the key idea behind natural selection on the AP Biology exam?
Focus on variation, heritability, and differential reproductive success. If a heritable trait helps individuals leave more surviving offspring in a specific environment, that trait can become more common over generations.
How is natural selection different from genetic drift?
Natural selection is nonrandom with respect to fitness: traits that improve survival or reproduction tend to increase. Genetic drift is random change in allele frequencies, strongest in small populations, such as founder effects or bottlenecks.
What mistakes are common in AP Biology natural selection questions?
Common mistakes include saying organisms evolve because they need to, treating individuals as if they evolve during their lifetime, and forgetting that selection depends on the environment.