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17. Types of Selection — Practice Questions 2
This chapter explores how natural, artificial, and sexual selection influence evolutionary change in populations through differential reproductive success.
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(Multiple Choice — Click to Reveal Answer)
1. What is the primary outcome of natural selection acting on heritable traits?
(A) Individuals adapt during their lifetime
(B) Populations become genetically identical
(C) Favorable alleles increase in frequency
(D) The environment evolves
Answer
(C) — Natural selection favors traits that improve survival and reproduction, increasing their frequency in the population.
2. Which selection type results in reduced genetic diversity around the average phenotype?
(A) Artificial selection
(B) Directional selection
(C) Stabilizing selection
(D) Disruptive selection
Answer
(C) — Stabilizing selection favors the mean phenotype and eliminates extremes, thus reducing genetic variation.
3. What is a likely evolutionary result when both extreme phenotypes confer an advantage in different microenvironments?
(A) Directional selection
(B) Genetic drift
(C) Stabilizing selection
(D) Disruptive selection
Answer
(D) — Disruptive selection favors individuals at both ends of the phenotypic spectrum in varied environments.
4. Which of the following is a valid example of intersexual selection?
(A) A lioness choosing a mate with the darkest mane
(B) Male deer locking antlers in combat
(C) Bacteria surviving antibiotics
(D) Male frogs inflating vocal sacs to intimidate other males
Answer
(A) — Intersexual selection involves mate choice, such as females choosing males with specific traits like mane darkness.
5. Why might vestigial structures be considered evidence for evolution?
(A) They improve an organism’s fitness
(B) They demonstrate new adaptations
(C) They are identical in all species
(D) They are remnants of traits functional in ancestors
Answer
(D) — Vestigial structures like the human tailbone suggest descent from ancestors where the structure had a function.
6. Which condition is necessary for evolution by natural selection to occur?
(A) Equal survival of all individuals
(B) High mutation rates only
(C) Heritable variation among individuals
(D) Unlimited resources
Answer
(C) — Heritable variation is required so that certain traits can be favored and passed on.
7. Which selection type typically occurs in a stable environment where the average trait provides the highest fitness?
(A) Disruptive selection
(B) Stabilizing selection
(C) Artificial selection
(D) Directional selection
Answer
(B) — Stabilizing selection favors the mean trait, often in stable environments.
8. How does artificial selection differ from natural selection in terms of selective pressure?
(A) There is no difference
(B) Artificial selection is random
(C) Humans determine the favored traits
(D) Artificial selection leads to extinction
Answer
(C) — In artificial selection, humans decide which traits to propagate, unlike natural environmental selection.
9. In directional selection, which of the following best describes the population’s response over time?
(A) The trait distribution becomes more variable
(B) The average phenotype shifts toward one extreme
(C) The population becomes less fit
(D) Genetic drift replaces selection
Answer
(B) — Directional selection causes a consistent shift in the average phenotype toward one extreme.
10. What would most likely occur in a population with no genetic variation?
(A) Rapid evolution
(B) Stabilizing selection
(C) No evolution by natural selection
(D) Increase in phenotype diversity
Answer
(C) — Without genetic variation, natural selection has nothing to act upon, preventing evolutionary change.
11. Which structure is an example of an analogous feature?
(A) Whale fin and bat wing
(B) Human hand and cat paw
(C) Butterfly wing and bat wing
(D) Dog tail and monkey tail
Answer
(C) — Analogous structures perform similar functions but evolved independently, like bat and butterfly wings.
12. What does differential reproductive success result in?
(A) All individuals producing the same number of offspring
(B) Decrease in population size
(C) Increase in favorable allele frequencies
(D) Equal survival among genotypes
Answer
(C) — Traits that lead to higher reproductive success become more common over generations.
13. Which of the following would be least likely to affect natural selection?
(A) Disease
(B) Genetic mutations
(C) Seasonal drought
(D) Identical genotypes
Answer
(D) — Identical genotypes offer no variation for natural selection to act upon.
14. In which scenario is sexual selection most clearly occurring?
(A) A bear hibernates in winter
(B) A fish changes scale color to attract a mate
(C) A rabbit escapes a fox
(D) A bird migrates seasonally
Answer
(B) — Changes to attract mates (like color display) are examples of sexual selection.
15. Why do populations evolve, but not individuals?
(A) Individuals can't inherit traits
(B) Evolution is a group behavior
(C) Genetic changes occur across generations, not within one organism
(D) Individuals don’t contain DNA
Answer
(C) — Evolution acts on populations over time through shifts in allele frequencies; individuals do not genetically change.
16. What is the function of molecular evidence in evolutionary studies?
(A) To analyze embryonic development
(B) To compare behavioral traits
(C) To determine evolutionary relationships by DNA similarity
(D) To evaluate fossil ages
Answer
(C) — DNA sequence comparisons are strong evidence for determining relatedness between species.
17. Which of the following supports the theory of common ancestry?
(A) Different metabolic pathways in all organisms
(B) Unique proteins in each species
(C) Universality of the genetic code
(D) Different DNA bases in each species
Answer
(C) — All organisms use the same basic genetic code, supporting the idea of a shared ancestor.
18. Which best describes how antibiotic resistance in bacteria evolves?
(A) Bacteria evolve new DNA from scratch
(B) Antibiotics create resistance in bacteria
(C) Mutations already present in some bacteria give them a survival advantage under antibiotic pressure
(D) Bacteria communicate resistance
Answer
(C) — Pre-existing mutations confer resistance; antibiotics select for those bacteria, increasing resistance frequency.
19. Which situation could cause stabilizing selection?
(A) Predators only target large and small individuals
(B) Humans breed animals for speed
(C) A changing climate favors long beaks
(D) Intermediate birth weights have highest survival rates
Answer
(D) — Stabilizing selection occurs when the average trait has the highest fitness, as in optimal birth weights.
20. Which is a likely result of disruptive selection on a trait like fur color in a varied habitat?
(A) Increase in intermediate fur color
(B) Shift to a single dominant color
(C) Elimination of all variation
(D) Rise in both dark and light fur colors, decrease in intermediate
Answer
(D) — Disruptive selection favors both extremes, leading to a drop in average/intermediate phenotypes.
21. What explains the widespread presence of TAS2R38 taster alleles in human populations?
(A) It enhances physical strength
(B) It increases mate attraction
(C) It provided a survival advantage by detecting toxic compounds
(D) It reduces nutrient absorption
Answer
(C) — The ability to detect bitterness helped early humans avoid toxins, improving survival.
22. Which of these is a real-time example of evolution occurring today?
(A) Extinction of dinosaurs
(B) Development of vestigial tails
(C) Industrial melanism in moths
(D) Increasing antibiotic resistance in bacteria
Answer
(D) — Bacterial resistance is a current, observable evolutionary process.
23. Why are fossil records limited in revealing all evolutionary history?
(A) All organisms fossilize easily
(B) Soft tissues don’t fossilize well
(C) Fossils provide DNA sequences
(D) Fossils show behaviors of ancient species
Answer
(B) — Soft tissues degrade quickly and are rarely preserved, limiting fossil evidence.
24. Which best describes convergent evolution?
(A) Organisms with shared ancestry develop different traits
(B) Unrelated species evolve similar traits due to similar environments
(C) Genetic drift causes identical traits
(D) All species merge into one
Answer
(B) — Convergent evolution occurs when unrelated species develop similar traits due to similar environmental pressures.
25. What type of trait is most likely to increase in frequency due to sexual selection?
(A) Trait improving camouflage
(B) Trait increasing metabolic rate
(C) Trait improving attraction to mates
(D) Trait lowering offspring number
Answer
(C) — Traits that increase mating success, like ornamentation or behavior, are favored by sexual selection.
26. A population of fish lives in a stream with both slow-moving and fast-moving water sections. Over time, large-bodied fish thrive in calm areas, and small-bodied fish dominate in rapid flows. What selection is this?
(A) Directional selection
(B) Stabilizing selection
(C) Disruptive selection
(D) Artificial selection
Answer
(C) — Disruptive selection favors both extremes depending on habitat zones, reducing survival of intermediate forms.
27. If a scientist observes that giraffes with medium-length necks are consistently outcompeted by both short- and long-necked individuals, which selection type is most likely occurring?
(A) Stabilizing
(B) Directional
(C) Disruptive
(D) Random
Answer
(C) — Disruptive selection favors both extremes while selecting against the intermediate trait.
28. Why is fitness best measured by reproductive success rather than survival alone?
(A) All surviving individuals pass on genes
(B) Only the strongest individuals survive
(C) Fitness reflects both survival and the ability to produce fertile offspring
(D) Fitness applies only to plants
Answer
(C) — In evolutionary terms, fitness means leaving viable offspring, not just surviving.
29. In a desert population of rodents, longer limbs allow individuals to outrun predators. After several generations, longer-limbed rodents dominate. What is this an example of?
(A) Stabilizing selection
(B) Genetic drift
(C) Directional selection
(D) Bottleneck effect
Answer
(C) — This is directional selection, where a beneficial extreme phenotype becomes more common over time.
30. Male elk grow large antlers that help them fight other males for mates. These antlers are energetically costly and attract predators. Why do they persist?
(A) They help elks escape predators
(B) They increase chances of mating, outweighing survival costs
(C) They are controlled by genetic drift
(D) They are vestigial structures
Answer
(B) — Despite survival disadvantages, the reproductive benefit sustains the trait through sexual selection.
31. A species of frogs exhibits variation in call pitch. In dense forests, low-pitch calls travel farther, and those males mate more often. What selection is at work?
(A) Stabilizing
(B) Directional
(C) Artificial
(D) Disruptive
Answer
(B) — Directional selection increases the frequency of low-pitched calls due to their mating advantage in a given environment.
32. If a population is subjected to strong stabilizing selection over many generations, which result is most likely?
(A) Emergence of extreme phenotypes
(B) Genetic diversity increases
(C) Average phenotype becomes more common
(D) All phenotypes disappear
Answer
(C) — Stabilizing selection increases the frequency of average traits and reduces extremes, narrowing variation.
33. A biologist finds two unrelated species of burrowing mammals with similar claws and digging behavior. What is the best explanation?
(A) Common ancestry
(B) Sexual selection
(C) Convergent evolution
(D) Artificial selection
Answer
(C) — Convergent evolution results in similar traits in unrelated species due to similar selective pressures.
34. Which best explains the rapid spread of pesticide resistance in a population of crop pests?
(A) Pesticides create new mutations
(B) Resistance genes were already present, and selection favored them
(C) All individuals developed resistance over time
(D) Resistance occurs only after population bottlenecks
Answer
(B) — Mutations conferring resistance preexist; selection increases their frequency in the presence of pesticides.
35. Which scenario would most clearly demonstrate sexual selection leading to extreme phenotypic traits?
(A) Camouflage helping prey avoid predators
(B) Mutation increasing limb length
(C) Females preferring males with elaborate feather displays
(D) Low-pitched frog calls spreading in noisy areas
Answer
(C) — Sexual selection often leads to exaggerated traits that increase mating success, even if costly in other aspects.
36. Explain how environmental changes can shift the type of natural selection acting on a population.
Answer
If the environment changes, different traits may provide a survival advantage, causing the type of selection (e.g., stabilizing, directional, or disruptive) to shift depending on which phenotypes are favored.
37. Why is it incorrect to say that individuals evolve in response to their environment?
Answer
Individuals do not evolve; only populations evolve over generations through changes in allele frequencies. Evolution requires differential reproductive success across many individuals.
38. Describe a real-world example of directional selection in nature.
Answer
The peppered moths in England experienced directional selection when industrial pollution darkened tree bark, favoring darker-colored moths that blended into the environment.
39. How can artificial selection reduce genetic diversity in a population?
Answer
Artificial selection focuses on breeding individuals with specific traits, often reducing variation by eliminating alleles not associated with desired traits.
40. Explain why sexual selection can lead to traits that may reduce an individual’s survival.
Answer
Sexual selection favors traits that improve mating success, such as bright colors or large antlers, even if those traits make the individual more visible to predators or energetically costly.
41. How do homologous structures support the theory of evolution?
Answer
Homologous structures share structural similarity due to common ancestry, even if their functions differ, indicating divergent evolution from a shared ancestor.
42. Why is molecular evidence, such as DNA sequence similarity, considered strong support for common ancestry?
Answer
DNA sequences are not easily altered by environmental factors and accumulate changes at a predictable rate, allowing scientists to compare organisms’ genetic similarity and infer evolutionary relationships.
43. What is meant by the term “fitness” in the context of natural selection?
Answer
Fitness refers to an individual’s ability to survive and reproduce, passing on its genes to the next generation. It is measured by reproductive success.
44. Describe how disruptive selection can maintain genetic variation in a population.
Answer
Disruptive selection favors individuals with extreme traits at both ends of the spectrum, maintaining multiple phenotypes and preserving variation within the population.
45. Provide an example of a vestigial structure and explain what it reveals about evolution.
Answer
The human tailbone (coccyx) is a vestigial structure, suggesting ancestral humans had tails. It indicates evolutionary change from an ancestor where the structure was functional.
46. How does sexual selection differ from natural selection?
Answer
Sexual selection involves traits that improve mating success, while natural selection involves traits that enhance survival. Both influence reproductive success but via different mechanisms.
47. Why might stabilizing selection occur in human birth weights?
Answer
Very low or very high birth weights are associated with higher infant mortality, so average weights are more likely to result in survival, leading to stabilizing selection for that trait.
48. Explain how biogeography provides evidence for evolution.
Answer
Biogeography studies the distribution of species across the globe. Closely related species are usually found near each other, reflecting common ancestry and geographic speciation.
49. What happens to alleles that reduce fitness in a population over generations?
Answer
Alleles that reduce fitness are less likely to be passed on and tend to decrease in frequency over time due to natural selection.
50. Describe how a mutation can contribute to evolution by natural selection.
Answer
If a mutation produces a trait that increases survival or reproduction in a given environment, natural selection may favor that trait, leading to its increased frequency in the population over generations.