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17. Types of Selection — Practice Questions
This chapter introduces natural, artificial, and sexual selection and how these processes drive evolutionary changes in populations.
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(Multiple Choice — Click to Reveal Answer)
1. What type of selection occurs when only one extreme phenotype provides a survival advantage?
(A) Stabilizing selection
(B) Disruptive selection
(C) Directional selection
(D) Artificial selection
Answer
(C) — Directional selection favors one extreme of the phenotypic range, shifting the population mean.
2. Which of the following is an example of artificial selection?
(A) Peppered moths in industrial England
(B) Beak size changes in Galápagos finches
(C) Breeding dogs for docile behavior
(D) Guppy color variation due to predators
Answer
(C) — Artificial selection is driven by humans, such as selectively breeding dogs for desired traits.
3. What type of selection favors individuals with average traits and selects against extremes?
(A) Directional
(B) Disruptive
(C) Sexual
(D) Stabilizing
Answer
(D) — Stabilizing selection reduces variation by selecting against extreme traits.
4. Which of the following best demonstrates intersexual selection?
(A) Males competing for mates
(B) Peahens choosing brighter peacocks
(C) Stronger males chasing off rivals
(D) Toads evolving toxin resistance
Answer
(B) — Intersexual selection involves mate choice, such as peahens preferring brighter males.
5. What kind of structure provides evidence of common ancestry but may serve different functions?
(A) Vestigial
(B) Analogous
(C) Homologous
(D) Convergent
Answer
(C) — Homologous structures share common ancestry but may have diverged in function.
6. Which of the following best describes disruptive selection?
(A) Selection that eliminates both extreme phenotypes
(B) Selection that favors both extreme phenotypes
(C) Selection that increases mutation rates
(D) Selection that stabilizes a population’s gene pool
Answer
(B) — Disruptive selection favors both extremes and selects against the intermediate phenotype.
7. What kind of evidence is considered strongest when determining evolutionary relationships?
(A) Fossil record
(B) Morphology
(C) DNA sequence comparison
(D) Geographic distribution
Answer
(C) — DNA sequences provide strong molecular evidence of common ancestry.
8. Which scenario is an example of directional selection?
(A) Birds with medium-length wings survive best
(B) Mice with either dark or light fur survive, but not gray
(C) Taller plants consistently produce more seeds
(D) All phenotypes survive equally
Answer
(C) — Directional selection favors one end of the phenotypic spectrum, like taller plants.
9. Which of the following best explains why bacteria can become resistant to antibiotics?
(A) All bacteria mutate when exposed to antibiotics
(B) Populations evolve through natural selection
(C) Antibiotics increase bacterial fitness
(D) Bacteria gain resistance by learning
Answer
(B) — Natural selection allows already-resistant bacteria to survive and reproduce.
10. Which term refers to anatomical structures that no longer serve a purpose?
(A) Homologous
(B) Analogous
(C) Convergent
(D) Vestigial
Answer
(D) — Vestigial structures are remnants of features that served functions in ancestors.
11. What does stabilizing selection typically reduce?
(A) Mean phenotype
(B) Variation in a trait
(C) Reproductive success
(D) Mutations
Answer
(B) — Stabilizing selection reduces variation by selecting against extreme phenotypes.
12. Which of the following is *not* a requirement for natural selection?
(A) Heritable variation
(B) Environmental pressure
(C) Equal survival of all individuals
(D) Differential reproductive success
Answer
(C) — Natural selection depends on unequal survival and reproduction.
13. Which of the following is most likely to occur during intrasexual selection?
(A) DNA mutation
(B) Mate choice by females
(C) Male competition for access to females
(D) Equal reproductive success
Answer
(C) — Intrasexual selection often involves competition among the same sex, usually males.
14. What would happen in a population if all individuals had identical genotypes?
(A) Natural selection would be stronger
(B) Evolution would proceed faster
(C) There would be no selection pressure
(D) No evolution by natural selection would occur
Answer
(D) — Without genetic variation, natural selection cannot act, so evolution cannot occur.
15. Which of the following best describes artificial selection?
(A) Natural survival advantage
(B) Mutation-driven evolution
(C) Human-directed breeding
(D) Environment-controlled mating
Answer
(C) — Artificial selection is controlled by humans to enhance desired traits.
16. What happens to alleles that confer a survival advantage over many generations?
(A) They decrease in frequency
(B) They are lost randomly
(C) They become fixed in the population
(D) They mutate more frequently
Answer
(C) — Advantageous alleles tend to increase in frequency and may become fixed.
17. Which observation supports evolution in current species?
(A) Identical fossils in distant continents
(B) The presence of tailbones in humans
(C) Bacterial resistance to antibiotics
(D) Similar embryos in mammals
Answer
(C) — Modern observations like antibiotic resistance provide real-time evidence of evolution.
18. Which term best describes structures that perform similar functions but evolved independently?
(A) Analogous
(B) Homologous
(C) Vestigial
(D) Genetic
Answer
(A) — Analogous structures serve similar functions but do not share common ancestry.
19. What is most directly measured by fitness in an evolutionary context?
(A) Mutation rate
(B) Physical strength
(C) Number of surviving offspring
(D) Speed of movement
Answer
(C) — Evolutionary fitness is defined by an individual's reproductive success.
20. What concept does the peppered moth example illustrate?
(A) Stabilizing selection
(B) Convergent evolution
(C) Directional selection
(D) Artificial selection
Answer
(C) — Environmental changes led to increased frequency of dark moths: classic directional selection.
21. In which type of selection does the average phenotype decrease in frequency over time?
(A) Disruptive
(B) Stabilizing
(C) Directional
(D) Random
Answer
(A) — Disruptive selection reduces the average phenotype in favor of both extremes.
22. The bright plumage of male peacocks is an example of:
(A) Stabilizing selection
(B) Artificial selection
(C) Intrasexual selection
(D) Intersexual selection
Answer
(D) — Intersexual selection involves mate choice based on traits like plumage brightness.
23. A farmer selects only the largest pumpkins for seed. This is:
(A) Natural selection
(B) Artificial selection
(C) Disruptive selection
(D) Stabilizing selection
Answer
(B) — The farmer is performing artificial selection by choosing specific traits to pass on.
24. Which situation would most likely lead to directional selection?
(A) No environmental change
(B) Introduction of a new predator
(C) No variation in the population
(D) Equal survival of all phenotypes
Answer
(B) — A new predator may create pressure favoring one extreme phenotype.
25. Which evidence supports that humans and chimpanzees share a recent common ancestor?
(A) Similar social behavior
(B) DNA sequence similarity
(C) Fossilized footprints
(D) Shared habitat preference
Answer
(B) — DNA sequence similarity is strong evidence of recent common ancestry.
26. A drought causes plants with soft seeds to die, favoring finches with large beaks. What type of selection is this?
(A) Stabilizing selection
(B) Sexual selection
(C) Directional selection
(D) Disruptive selection
Answer
(C) — Directional selection favors finches with larger beaks, shifting the average phenotype.
27. A population of birds has some individuals with dull feathers and others with bright feathers. Bright males attract mates but are more visible to predators. What type of evolutionary force is acting here?
(A) Disruptive selection
(B) Intersexual selection
(C) Genetic drift
(D) Artificial selection
Answer
(B) — This is intersexual selection, as mate preference (not survival) drives reproductive success.
28. If a gene gives bacteria resistance to an antibiotic, what best explains the gene’s increased frequency over time?
(A) Mutation due to the antibiotic
(B) Horizontal gene transfer
(C) Increased reproductive success
(D) Genetic bottleneck
Answer
(C) — Resistant bacteria reproduce more successfully in antibiotic environments, increasing gene frequency.
29. Which type of selection reduces variation by selecting against both extreme phenotypes?
(A) Directional
(B) Disruptive
(C) Stabilizing
(D) Sexual
Answer
(C) — Stabilizing selection increases frequency of the intermediate phenotype and reduces extremes.
30. In a species of fish, small and large males both have mating advantages, but medium-sized males do not. What type of selection is acting on this population?
(A) Stabilizing
(B) Artificial
(C) Directional
(D) Disruptive
Answer
(D) — Disruptive selection favors both extremes and selects against the average.
31. Why are homologous structures considered evidence of evolution?
(A) They have similar functions in unrelated species
(B) They arise due to convergent evolution
(C) They suggest common ancestry despite different functions
(D) They are vestigial features in living organisms
Answer
(C) — Homologous structures indicate shared ancestry due to similar structure despite different use.
32. A scientist wants to determine how closely two species are related. Which evidence is most conclusive?
(A) Mating rituals
(B) Shared behavior
(C) DNA sequence comparison
(D) Fossil location
Answer
(C) — DNA sequence comparisons provide the most precise evidence of evolutionary relationships.
33. A trait becomes more frequent in a population because females prefer it in mates. Which statement is correct?
(A) The trait provides a survival advantage
(B) The trait is a result of stabilizing selection
(C) The trait evolved through sexual selection
(D) The trait is always disadvantageous
Answer
(C) — Traits that increase mating success, even if costly for survival, evolve via sexual selection.
34. Which process would most likely cause a rapid change in the gene pool of a small population after a natural disaster?
(A) Sexual selection
(B) Gene flow
(C) Genetic drift
(D) Stabilizing selection
Answer
(C) — Genetic drift causes random changes in allele frequency, especially in small populations.
35. Over several generations, farmers breed cows that produce the most milk. What type of selection does this demonstrate?
(A) Natural selection
(B) Sexual selection
(C) Artificial selection
(D) Disruptive selection
Answer
(C) — Artificial selection is human-driven breeding for specific traits like milk production.
36. Explain why populations, rather than individuals, evolve over time.
Answer
Evolution occurs due to changes in allele frequencies across generations, which can only happen in populations. Individual traits don’t change genetically during a lifetime.
37. Why is variation in a population essential for natural selection to occur?
Answer
Without variation, all individuals would have the same traits, and there would be no differences for natural selection to act upon.
38. Describe how directional selection would affect the trait distribution in a population over time.
Answer
Directional selection shifts the trait distribution toward one extreme phenotype, increasing its frequency while reducing the other.
39. How does artificial selection differ from natural selection?
Answer
Artificial selection is driven by human choice for desired traits, while natural selection is driven by environmental pressures affecting survival and reproduction.
40. Why might a sexually selected trait decrease an individual's survival, yet still increase in frequency?
Answer
Traits that attract mates (like bright colors) can increase reproductive success despite reducing survival, leading to higher trait frequency.
41. A certain species of beetle is preyed upon by birds. Explain how disruptive selection could affect beetle coloration in a habitat with both dark and light patches.
Answer
Beetles with dark or light coloration would blend in and survive, while medium-colored beetles would be more visible and selected against, increasing both extremes.
42. Why are DNA sequences considered strong evidence for common ancestry?
Answer
DNA sequences change slowly and consistently over time, so closely related species share more sequence similarity, reflecting recent common ancestry.
43. A population of moths shifts from mostly dark-colored to mostly light-colored over generations. What does this indicate?
Answer
This suggests directional selection favoring light-colored moths, possibly due to environmental change like lighter backgrounds or reduced pollution.
44. Describe the role of differential reproductive success in natural selection.
Answer
Individuals with favorable traits are more likely to survive and reproduce, passing on those traits and increasing their frequency in the population.
45. What evidence supports the claim that species A and species B share a recent common ancestor?
Answer
If they share a high percentage of DNA sequence similarity or homologous structures, this supports a recent common ancestor.
46. In what situation might stabilizing selection be most beneficial to a population?
Answer
When the environment remains constant and intermediate traits provide the highest survival, stabilizing selection helps maintain the optimal phenotype.
47. A student claims that individuals evolve during their lifetime to survive. Why is this incorrect?
Answer
Evolution refers to changes in a population’s gene pool over generations; individuals cannot genetically change traits during their life.
48. Describe how natural selection can lead to antibiotic resistance in bacteria.
Answer
Resistant bacteria survive antibiotic treatment and reproduce, passing on resistance genes. Over time, the population becomes mostly resistant.
49. What is a vestigial structure, and how does it provide evidence for evolution?
Answer
Vestigial structures are remnants of functional features in ancestors. Their presence suggests that organisms have evolved from ancestors with different lifestyles or environments.
50. Why do some traits that reduce survival still persist in a population?
Answer
Traits that improve reproductive success (e.g., via sexual selection) may persist even if they reduce individual survival because they increase offspring production.