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📝 Charles Darwin and theory of natural selection (10 MCQs)

📖 From Campbell Biology • 1. Evolution and the theme of Biology and Scientific Inquiry • 10 questions available

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What is Charles Darwin and theory of natural selection?

Definition:
Charles Darwin was the 19th-century naturalist who, along with Alfred Russel Wallace, proposed the theory of natural selection as the mechanism for evolution, based on observations of variation, inheritance, and competition in nature, where individuals with advantageous traits are more likely to survive, reproduce, and pass those traits to offspring, leading to gradual change in populations over generations.

Working:
Natural selection works through three key principles: variation exists within populations, heritable traits are passed from parents to offspring, and differential reproductive success means that individuals with traits better suited to their environment produce more offspring, thereby increasing the frequency of those traits in the gene pool, and this process is often summarized by the equation $\text{Fitness} = \frac{\text{Number of Offspring Produced}}{\text{Average Offspring in Population}}$ , with higher fitness individuals contributing more to the next generation.

Example:
A simple example is the finches of the Galápagos Islands, where during dry seasons, finches with larger, stronger beaks were better able to crack tough seeds and survive, passing the large-beak trait to offspring, and over time, the average beak size in the population increased, illustrating natural selection in action.

Reason:
Darwin's theory of natural selection is the central organizing principle of biology, explaining the diversity and adaptation of life, and it underpins modern fields like genetics, ecology, and medicine, providing the framework for understanding antibiotic resistance, vaccine development, and conservation biology.

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📝 All Charles Darwin and theory of natural selection MCQs

Q1. Which observation most directly supports Darwin's explanation that natural selection can change populations over generations?

A.Individual organisms intentionally develop useful traits when conditions change

B.Individuals with heritable traits that improve survival and reproduction tend to leave more offspring ✅

C.All organisms gradually become more complex because evolution always favors complexity

D.Environmental conditions directly transform an organism's genes in the same way during its lifetime

💡 Difficulty: easy | ✅ Correct: B

📖 Explanation: Natural selection acts on differences among individuals, but evolutionary change occurs across generations when advantageous heritable traits become more common. Individuals do not intentionally develop useful traits, and environmental effects during one lifetime do not automatically create inherited adaptations.

Q2. A population of beetles contains green and brown individuals. Birds more easily detect green beetles on dark soil, while color differences are heritable. After many generations, which prediction is most consistent with natural selection?

A.Brown beetles should become more common because they are harder for birds to detect ✅

B.Green beetles should disappear immediately because predators always remove unfavorable traits

C.Both colors should remain equally common because predators do not affect evolution

D.Brown beetles should intentionally produce more brown offspring after experiencing predation

💡 Difficulty: easy | ✅ Correct: A

📖 Explanation: If brown coloration provides better camouflage and the difference is heritable, brown beetles are more likely to survive and reproduce. Over generations, the frequency of brown coloration should therefore increase, assuming other evolutionary forces do not dominate.

Q3. Two populations of the same insect species experience different environments. In Environment X, individuals with thicker shells survive predators more often; in Environment Y, shell thickness has little effect, but faster movement improves survival. Which conclusion is strongest?

A.Natural selection must favor thicker shells in both environments

B.The same trait must always be advantageous within a species

C.Different environments can favor different heritable traits, causing populations to diverge over time ✅

D.Natural selection causes organisms in each environment to develop the needed trait intentionally

💡 Difficulty: medium | ✅ Correct: C

📖 Explanation: Natural selection depends on how traits affect reproductive success under particular environmental conditions. A trait advantageous in one environment may provide little benefit elsewhere, so different selective pressures can cause populations of the same species to change in different directions.

Q4. A student argues: 'Giraffes stretched their necks to reach higher leaves, so their offspring inherited the longer necks acquired by their parents.' Which criticism best identifies the problem with this reasoning from a natural-selection perspective?

A.It assumes all giraffes have identical genes

B.It treats an acquired change during an individual's lifetime as automatically becoming a heritable population change ✅

C.It assumes food availability can never affect survival

D.It correctly describes natural selection because effort directly changes inherited traits

💡 Difficulty: medium | ✅ Correct: B

📖 Explanation: Natural selection requires heritable variation that already exists or arises through genetic processes. An individual's increased effort or acquired characteristic does not automatically become inherited by offspring. Evolution instead reflects differences in reproductive success associated with heritable traits.

Q5. A researcher measures the proportion of a heritable advantageous trait in a population: Generation 1 = 10%, Generation 2 = 18%, Generation 3 = 31%, Generation 4 = 47%, Generation 5 = 64%. Which interpretation is best supported by these data?

A.The trait is becoming more common across generations, consistent with directional selection ✅

B.The trait is becoming less common because its percentage never reaches 100%

C.The data prove that every individual developed the trait because of environmental demand

D.The population is not evolving because some individuals still lack the trait

💡 Difficulty: medium | ✅ Correct: A

📖 Explanation: The increasing proportion of the advantageous heritable trait indicates that its frequency is rising through successive generations. This pattern is consistent with natural selection favoring the trait, although the data alone do not prove that selection is the only evolutionary mechanism involved.

Q6. A population initially contains 70% individuals with trait X and 30% with trait Y. Trait Y is heritable and provides greater resistance to a newly introduced predator. After several generations, trait Y reaches 75%. Which sequence best explains the change?

A.Predator exposure creates trait Y in every individual, followed by inheritance

B.Trait Y reduces reproduction, but its frequency rises because organisms evolve toward complexity

C.Heritable variation exists, predators differentially affect survival or reproduction, and individuals with trait Y contribute more offspring ✅

D.Predators directly choose which genes offspring receive, causing trait Y to spread

💡 Difficulty: hard | ✅ Correct: C

📖 Explanation: The scenario follows the logic of natural selection: heritable variation is present, the environment creates differential survival or reproduction, and individuals with the advantageous phenotype contribute disproportionately to later generations. Repeated differences in reproductive success alter trait frequencies.

Q7. A scientist compares two populations and records the frequency of a favored allele over time. Population A rises from 0.20 to 0.82 in 12 generations, while Population B remains near 0.20. Assuming similar starting conditions, what is the most reasonable interpretation?

A.Selection favoring the allele may be stronger or more consistently effective in Population A ✅

B.Population B must have stopped reproducing entirely

C.The allele cannot be heritable in Population A because its frequency changed

D.Natural selection always produces identical rates of change in all populations

💡 Difficulty: hard | ✅ Correct: A

📖 Explanation: A rapid increase in the frequency of a favored heritable allele is consistent with stronger or more persistent selection in Population A. The comparison does not establish that Population B stopped reproducing or that natural selection must operate at the same rate everywhere.

Q8. A population of moths contains light and dark forms. Before industrial pollution, light moths are more common; after tree surfaces become darker, dark moths become more common. A student concludes, 'The pollution changed each light moth into a dark moth.' What is the better interpretation?

A.Pollution directly converted every moth, and the new color was necessarily inherited

B.Dark moths likely had a preexisting heritable advantage in the changed environment and left more offspring ✅

C.Pollution caused all moths to choose darker colors during mating

D.The observation cannot involve natural selection because the environment changed

💡 Difficulty: hard | ✅ Correct: B

📖 Explanation: A change in environmental conditions can alter which existing heritable phenotypes have higher survival or reproductive success. If dark moths were already present and became better camouflaged, their greater contribution to subsequent generations could increase the frequency of dark coloration.

Q9. Suppose a population has three heritable phenotypes. Their relative reproductive successes are 1.0, 1.5, and 0.8 in the same environment. If these differences persist for many generations and other factors are negligible, which phenotype is expected to increase most strongly in frequency?

A.The phenotype with reproductive success 0.8

B.The phenotype with reproductive success 1.0

C.The phenotype with reproductive success 1.5 ✅

D.All three should increase equally because natural selection preserves variation

💡 Difficulty: easy | ✅ Correct: C

📖 Explanation: Relative reproductive success determines how strongly phenotypes contribute to future generations. The phenotype with a value of 1.5 leaves more descendants on average than the alternatives, so its associated heritable traits are expected to become more common over generations.

Q10. Darwin observed that related organisms can differ in traits and that environments impose different challenges. Which combination of ideas provides the strongest basis for explaining adaptation by natural selection?

A.Heritable variation, competition or differential survival, and unequal reproductive success ✅

B.Perfect organisms, intentional adaptation, and inheritance of every acquired characteristic

C.Environmental change alone, without variation among individuals

D.Random changes in traits followed by guaranteed survival of the most complex organisms

💡 Difficulty: easy | ✅ Correct: A

📖 Explanation: Natural selection requires variation among individuals, some component of that variation must be heritable, and individuals must differ in survival or reproductive success. Across generations, these differences can shift population characteristics, producing adaptation without requiring purposeful change.

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