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17. Types of Selection — Practice Questions 3
This chapter explains the mechanisms and consequences of natural, sexual, and artificial selection in shaping traits across generations.
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(Multiple Choice — Click to Reveal Answer)
1. Which of the following is NOT a necessary condition for natural selection?
(A) Variation in traits
(B) Heritability of traits
(C) Unlimited resources
(D) Differential survival or reproduction
Answer
(C) — Natural selection relies on limited resources, creating competition that drives differential reproductive success.
2. Which example best illustrates intrasexual selection?
(A) Female birds choosing males with brighter feathers
(B) Male deer fighting for access to females
(C) Bacteria evolving antibiotic resistance
(D) Plants producing more seeds in sunlight
Answer
(B) — Intrasexual selection involves members of the same sex competing, such as male deer fighting.
3. Which statement best explains the role of mutations in evolution by natural selection?
(A) Mutations always cause harmful traits
(B) Mutations are selected based on how well they improve survival
(C) Mutations arise when needed to adapt
(D) Natural selection causes mutations to occur
Answer
(B) — While mutations occur randomly, those that improve survival and reproduction are favored by natural selection.
4. What does directional selection do to the phenotypic distribution in a population?
(A) It splits it into two peaks
(B) It narrows the curve around the average
(C) It shifts the curve toward one extreme
(D) It causes random changes
Answer
(C) — Directional selection favors one extreme, shifting the distribution toward that phenotype.
5. Which of the following is an example of evolution currently observable in real time?
(A) Development of the horse’s leg structure
(B) Human ancestors walking upright
(C) Increase of pesticide resistance in insects
(D) Transition of fish to amphibians
Answer
(C) — Insect populations evolving resistance to pesticides is a modern, observable example of natural selection.
6. Which of the following best defines fitness in evolutionary biology?
(A) Physical strength and endurance
(B) Ability to find food
(C) Number of fertile offspring produced
(D) Ability to dominate other individuals
Answer
(C) — In evolution, fitness refers to an individual’s reproductive success, measured by the number of offspring that survive and reproduce.
7. What is the result of stabilizing selection over several generations?
(A) Increased trait variation
(B) Selection of extreme phenotypes
(C) Reduced phenotypic variation around a mean
(D) Elimination of all genetic diversity
Answer
(C) — Stabilizing selection favors average traits and reduces the presence of extremes.
8. Which condition would most likely lead to directional selection?
(A) Stable environment
(B) Environment with shifting conditions
(C) Equal reproductive success
(D) No competition for resources
Answer
(B) — Changing environmental conditions can favor one extreme phenotype, leading to directional selection.
9. What kind of evidence do homologous structures provide?
(A) Evidence of convergent evolution
(B) Evidence of common ancestry
(C) Evidence of sexual selection
(D) Evidence of environmental pressures
Answer
(B) — Homologous structures have similar anatomy but different functions, indicating shared ancestry.
10. Why is genetic variation important in natural selection?
(A) It prevents extinction
(B) It allows adaptation to new environments
(C) It increases mutation rates
(D) It eliminates competition
Answer
(B) — Genetic variation provides the raw material for natural selection to act upon, allowing populations to adapt.
11. What is sexual selection primarily concerned with?
(A) Survival
(B) Mating success
(C) Foraging efficiency
(D) Disease resistance
Answer
(B) — Sexual selection favors traits that improve chances of finding or attracting mates.
12. Which of the following scenarios represents artificial selection?
(A) Wolves evolving thick fur in cold climates
(B) Birds evolving longer beaks due to food availability
(C) Farmers breeding cows for higher milk production
(D) Fish adapting to deeper waters
Answer
(C) — In artificial selection, humans intentionally select for specific traits like higher milk yield.
13. What would happen if all individuals in a population were genetically identical?
(A) Selection would speed up
(B) Natural selection could not occur
(C) Sexual selection would increase
(D) Evolution would accelerate
Answer
(B) — Without variation, there are no differential traits for natural selection to favor or eliminate.
14. Which type of selection may lead to speciation under long-term pressure?
(A) Disruptive selection
(B) Stabilizing selection
(C) Random mating
(D) Sexual selection
Answer
(A) — Disruptive selection favors extremes and can split populations into distinct groups, potentially leading to speciation.
15. Which factor most directly affects allele frequencies in a population over time?
(A) Fitness
(B) Behavior
(C) Environment
(D) Temperature
Answer
(A) — Fitness determines which alleles are passed on more frequently, directly impacting allele frequencies.
16. In sexual selection, what often determines reproductive success in males?
(A) Hiding from predators
(B) Ability to avoid disease
(C) Success in male-male competition or attractiveness to females
(D) Fast metabolism
Answer
(C) — Males often compete for mates or are chosen by females based on certain traits.
17. What kind of trait is most likely to persist under stabilizing selection?
(A) A very rare trait
(B) The intermediate trait
(C) A new mutation
(D) A neutral allele
Answer
(B) — Stabilizing selection increases the frequency of intermediate traits that offer survival or reproductive advantages.
18. Which of the following represents evolution?
(A) A mutation in one individual
(B) A change in allele frequencies in a population over time
(C) A new predator entering a habitat
(D) A shift in climate
Answer
(B) — Evolution is defined as a change in the genetic makeup of a population over generations.
19. What is the main goal of evolutionary adaptation?
(A) Increasing population size
(B) Improving physical appearance
(C) Enhancing reproductive success in a given environment
(D) Creating genetic diversity
Answer
(C) — Adaptations improve survival and reproduction in a specific environment.
20. Which type of selection might maintain two different fur colors in a rabbit population if each color has a survival benefit in different habitats?
(A) Directional
(B) Stabilizing
(C) Disruptive
(D) Artificial
Answer
(C) — Disruptive selection favors individuals at both extremes, such as two different fur colors.
21. Why does convergent evolution result in similar traits in unrelated species?
(A) They share a recent common ancestor
(B) They face similar environmental pressures
(C) They have similar DNA sequences
(D) They experience identical mutations
Answer
(B) — Similar environments can lead to similar adaptations even in unrelated species.
22. Why are vestigial structures considered evidence of evolution?
(A) They serve new functions in modern species
(B) They indicate environmental stability
(C) They are remnants of ancestral traits
(D) They show natural selection doesn’t occur
Answer
(C) — Vestigial structures are leftover features that were functional in ancestral organisms.
23. What evolutionary pattern is observed in male birds that develop increasingly colorful plumage due to female preference?
(A) Artificial selection
(B) Stabilizing selection
(C) Disruptive selection
(D) Sexual selection
Answer
(D) — This is sexual selection, where traits are favored because they enhance mating success.
24. Which of these is most likely a result of stabilizing selection on human birth weight?
(A) Increased variation in birth size
(B) Elimination of all small infants
(C) Maintenance of average-weight births
(D) Only large babies surviving
Answer
(C) — Infants of average weight have higher survival rates, which stabilizing selection reinforces.
25. What is the role of the environment in natural selection?
(A) It creates mutations
(B) It directly changes genes
(C) It determines which traits are advantageous
(D) It produces individuals with higher fitness
Answer
(C) — The environment shapes which traits increase survival and reproduction, guiding natural selection.
26. A population of beetles lives in an area with both light and dark rocks. Over time, only light-colored and dark-colored beetles thrive, while medium-colored ones are eaten. What type of selection is this?
(A) Directional selection
(B) Stabilizing selection
(C) Disruptive selection
(D) Artificial selection
Answer
(C) — Disruptive selection favors both extremes over the intermediate phenotype, reducing the frequency of the average form.
27. Which of the following best explains how sexual selection can lead to traits that reduce an individual’s survival?
(A) The traits make predators less likely to attack
(B) The traits improve ability to hide
(C) The traits enhance mating success even if they are risky
(D) The traits only appear after reproduction
Answer
(C) — Sexual selection may favor traits like bright colors or large antlers that attract mates but also predators.
28. What would be the long-term result of stabilizing selection on a population's genetic diversity?
(A) Increase in extremes
(B) Increase in mutation rate
(C) Decrease in genetic diversity
(D) Constant introduction of new alleles
Answer
(C) — Stabilizing selection reduces variation by eliminating extremes, thus decreasing genetic diversity over time.
29. How does genetic drift differ from natural selection?
(A) It is non-random
(B) It favors beneficial traits
(C) It changes allele frequencies due to chance
(D) It requires competition for mates
Answer
(C) — Genetic drift is a random process, especially significant in small populations, unrelated to fitness.
30. A biologist finds two unrelated species that both have long, sticky tongues for catching insects. What type of evolution is this an example of?
(A) Divergent evolution
(B) Genetic drift
(C) Convergent evolution
(D) Sexual selection
Answer
(C) — Convergent evolution occurs when unrelated organisms develop similar traits due to similar environments or functions.
31. In a population where female peacocks prefer brightly colored males, what process is shaping the evolution of male coloration?
(A) Stabilizing selection
(B) Intersexual selection
(C) Intrasexual selection
(D) Genetic bottleneck
Answer
(B) — Intersexual selection involves one sex (usually females) choosing mates based on specific traits.
32. In a stable environment, a population has less genetic variation and consistently favors average phenotypes. Which statement best explains this?
(A) The population experiences random mutations
(B) Directional selection is acting
(C) Stabilizing selection is eliminating extremes
(D) The population is in Hardy-Weinberg equilibrium
Answer
(C) — Stabilizing selection in a stable environment maintains the status quo by favoring average traits and eliminating outliers.
33. Which factor would most likely maintain high genetic diversity in a population?
(A) Stabilizing selection
(B) Directional selection
(C) Disruptive selection
(D) Founder effect
Answer
(C) — Disruptive selection maintains diversity by favoring opposite extremes rather than the mean.
34. What evolutionary force most likely explains a sudden rise in a rare allele after a natural disaster wipes out much of a population?
(A) Gene flow
(B) Sexual selection
(C) Genetic drift
(D) Stabilizing selection
Answer
(C) — Genetic drift can cause random allele frequency shifts, especially after population bottlenecks.
35. Which of the following is an example of directional selection in agriculture?
(A) Farmers preserving both small and large apple trees
(B) Farmers only breeding cows with the highest milk yield
(C) Farmers maintaining cows of average weight
(D) Farmers avoiding extreme traits
Answer
(B) — Breeding only high-yield individuals is directional selection, favoring one end of the trait spectrum.
36. Describe how a change in environmental conditions might trigger directional selection in a population.
Answer
If the environment changes in a way that favors one extreme trait (e.g., colder climate favoring thicker fur), individuals with that trait have higher survival and reproductive success, shifting the population average over generations.
37. Why is sexual selection considered a special case of natural selection?
Answer
Sexual selection affects reproductive success specifically through mate choice or competition, making it a subset of natural selection that focuses on traits enhancing mating success rather than survival alone.
38. How can disruptive selection potentially lead to the formation of new species?
Answer
If individuals at both extremes of a trait are favored and interbreeding between the groups decreases, reproductive isolation may occur over time, potentially leading to speciation.
39. Why do vestigial structures provide evidence for common ancestry?
Answer
Vestigial structures are inherited from ancestors in which they had a function. Their presence in modern organisms suggests a shared evolutionary origin with those ancestors.
40. Explain how artificial selection differs from natural selection in terms of driving forces and outcomes.
Answer
Artificial selection is driven by human preference for certain traits, often leading to rapid changes, whereas natural selection is driven by environmental pressures and results in traits that improve survival and reproduction.
41. What is an example of intersexual selection in the animal kingdom, and how does it influence evolution?
Answer
Peahens preferring males with brighter tails is intersexual selection. Over time, this preference increases the frequency of the trait, even if it doesn't directly benefit survival.
42. How does molecular evidence, such as DNA similarity, support evolutionary relationships?
Answer
Closely related organisms share more similar DNA sequences, indicating a common ancestor. The degree of similarity helps scientists infer how recently species diverged.
43. Why might stabilizing selection be common in human traits such as birth weight?
Answer
Very low or very high birth weights can be risky for infant survival, so intermediate weights are favored, reducing variation through stabilizing selection.
44. Explain why populations, not individuals, evolve over time.
Answer
Evolution involves changes in allele frequencies across generations. Individuals don’t change their genetics; instead, traits become more or less common in the population based on reproductive success.
45. Describe how antibiotic resistance in bacteria is an example of natural selection.
Answer
Resistant bacteria survive antibiotic exposure and reproduce more than non-resistant ones. Over time, the population shifts to contain mostly resistant individuals — a clear case of natural selection.
46. How does gene flow affect variation in a population?
Answer
Gene flow introduces new alleles into a population when individuals migrate and breed, increasing genetic variation and potentially altering allele frequencies.
47. Why is it important for evolutionary biologists to distinguish between analogous and homologous structures?
Answer
Homologous structures suggest shared ancestry, while analogous structures result from convergent evolution. Distinguishing between them helps determine evolutionary relationships accurately.
48. How can a single mutation lead to evolutionary change in a population?
Answer
If the mutation provides a reproductive or survival advantage, individuals with it may produce more offspring. Over time, the allele can increase in frequency, contributing to evolution.
49. What is the relationship between environmental pressures and selection of traits?
Answer
Environmental pressures determine which traits are advantageous. Individuals with those traits survive and reproduce more, causing the traits to become more common in the population.
50. How might sexual dimorphism arise through the process of sexual selection?
Answer
Sexual dimorphism arises when one sex (often males) evolves distinct traits to compete for or attract mates. Over time, these traits diverge from the other sex due to sexual selection pressures.