,Chapter 1 – Adaptation by Natural Selection
Theme: Introduces Darwin’s theory of natural selection. Explains adaptation,
fitness, and how traits spread in populations.
Test Bank (20 Questions)
1. Which concept best explains why certain traits increase in frequency
within a population over multiple generations?
A. Genetic drift
B. Mutation
C. Natural selection
D. Recombination
✅ Correct Answer: C
Rationale: Natural selection is the differential survival and reproduction of
individuals due to advantageous phenotypic traits. Mutations and
recombination generate variation, while genetic drift changes allele
frequencies randomly, but only natural selection consistently favors traits that
increase fitness.
2. A farmer notices that in his cornfield, plants with deeper roots survive a
summer drought better than those with shallow roots. What evolutionary
mechanism would most likely cause deeper root traits to become more
common in future generations?
A. Mutation
B. Natural selection
C. Gene flow
D. Genetic drift
✅ Correct Answer: B
Rationale: Deeper roots enhance drought survival, increasing the
,reproductive success of plants with this trait. Over time, natural selection
would increase the frequency of deeper root alleles in the population.
3. How does the concept of “fitness” in evolutionary biology differ from its
everyday usage?
A. Fitness means physical strength in both biology and common use
B. In biology, fitness is defined as reproductive success, not physical ability
C. Fitness refers only to survival, not reproduction, in evolutionary theory
D. Fitness means genetic similarity to ancestors in evolutionary biology
✅ Correct Answer: B
Rationale: Biological fitness is measured by the number of viable offspring
an individual contributes to the next generation, not by physical strength or
mere survival.
4. Which of the following best illustrates directional selection?
A. A population of birds in which individuals with intermediate-sized beaks
survive best
B. A population of moths shifting from mostly light-colored to mostly dark-
colored forms due to pollution
C. A population of fish maintaining two distinct coloration morphs due to
mate preference
D. A population of flowers displaying both very small and very large
blossoms
✅ Correct Answer: B
Rationale: Directional selection shifts the population toward one extreme
phenotype, as seen in moths becoming darker in polluted environments.
Stabilizing selection favors intermediates, while disruptive selection favors
extremes.
, 5. Why does natural selection act on phenotypes rather than directly on
genotypes?
A. Phenotypes are always heritable, while genotypes are not
B. Phenotypes are the observable traits subject to environmental pressures
C. Genotypes cannot change in frequency across generations
D. Natural selection operates only on random genetic mutations
✅ Correct Answer: B
Rationale: Selection pressures act on expressed traits (phenotypes). The
underlying genotypes shift in frequency only because phenotypic differences
affect survival and reproduction.
6. When malaria is common in a region, why is the sickle-cell allele
maintained in human populations despite its harmful effects in homozygotes?
A. It is a neutral mutation with no effect on survival
B. It is linked to beneficial mutations in other genes
C. Heterozygotes have increased resistance to malaria
D. Homozygotes with the allele have greater reproductive success
✅ Correct Answer: C
Rationale: This is a classic case of balancing selection, where heterozygotes
benefit from malaria resistance, maintaining the allele in the population
despite its negative effects in homozygotes.
7. What role does variation play in the process of natural selection?
A. Variation reduces the rate of evolution by increasing randomness
B. Variation provides the raw material on which natural selection can act
C. Variation guarantees that all individuals have equal survival chances
D. Variation only arises when populations face environmental stress
✅ Correct Answer: B
Rationale: Without heritable variation in traits, natural selection cannot favor
some individuals over others, and evolution by natural selection would not
occur.
Theme: Introduces Darwin’s theory of natural selection. Explains adaptation,
fitness, and how traits spread in populations.
Test Bank (20 Questions)
1. Which concept best explains why certain traits increase in frequency
within a population over multiple generations?
A. Genetic drift
B. Mutation
C. Natural selection
D. Recombination
✅ Correct Answer: C
Rationale: Natural selection is the differential survival and reproduction of
individuals due to advantageous phenotypic traits. Mutations and
recombination generate variation, while genetic drift changes allele
frequencies randomly, but only natural selection consistently favors traits that
increase fitness.
2. A farmer notices that in his cornfield, plants with deeper roots survive a
summer drought better than those with shallow roots. What evolutionary
mechanism would most likely cause deeper root traits to become more
common in future generations?
A. Mutation
B. Natural selection
C. Gene flow
D. Genetic drift
✅ Correct Answer: B
Rationale: Deeper roots enhance drought survival, increasing the
,reproductive success of plants with this trait. Over time, natural selection
would increase the frequency of deeper root alleles in the population.
3. How does the concept of “fitness” in evolutionary biology differ from its
everyday usage?
A. Fitness means physical strength in both biology and common use
B. In biology, fitness is defined as reproductive success, not physical ability
C. Fitness refers only to survival, not reproduction, in evolutionary theory
D. Fitness means genetic similarity to ancestors in evolutionary biology
✅ Correct Answer: B
Rationale: Biological fitness is measured by the number of viable offspring
an individual contributes to the next generation, not by physical strength or
mere survival.
4. Which of the following best illustrates directional selection?
A. A population of birds in which individuals with intermediate-sized beaks
survive best
B. A population of moths shifting from mostly light-colored to mostly dark-
colored forms due to pollution
C. A population of fish maintaining two distinct coloration morphs due to
mate preference
D. A population of flowers displaying both very small and very large
blossoms
✅ Correct Answer: B
Rationale: Directional selection shifts the population toward one extreme
phenotype, as seen in moths becoming darker in polluted environments.
Stabilizing selection favors intermediates, while disruptive selection favors
extremes.
, 5. Why does natural selection act on phenotypes rather than directly on
genotypes?
A. Phenotypes are always heritable, while genotypes are not
B. Phenotypes are the observable traits subject to environmental pressures
C. Genotypes cannot change in frequency across generations
D. Natural selection operates only on random genetic mutations
✅ Correct Answer: B
Rationale: Selection pressures act on expressed traits (phenotypes). The
underlying genotypes shift in frequency only because phenotypic differences
affect survival and reproduction.
6. When malaria is common in a region, why is the sickle-cell allele
maintained in human populations despite its harmful effects in homozygotes?
A. It is a neutral mutation with no effect on survival
B. It is linked to beneficial mutations in other genes
C. Heterozygotes have increased resistance to malaria
D. Homozygotes with the allele have greater reproductive success
✅ Correct Answer: C
Rationale: This is a classic case of balancing selection, where heterozygotes
benefit from malaria resistance, maintaining the allele in the population
despite its negative effects in homozygotes.
7. What role does variation play in the process of natural selection?
A. Variation reduces the rate of evolution by increasing randomness
B. Variation provides the raw material on which natural selection can act
C. Variation guarantees that all individuals have equal survival chances
D. Variation only arises when populations face environmental stress
✅ Correct Answer: B
Rationale: Without heritable variation in traits, natural selection cannot favor
some individuals over others, and evolution by natural selection would not
occur.
