In evolutionary biology, "fitness" refers to

Answer: An individual's ability to survive and reproduce, contributing alleles to the next generation Fitness measures reproductive success — passing genes on. A weaker organism with more offspring has higher fitness than a stronger one with none.

Natural selection acts directly on

Answer: Phenotypes (and indirectly on the alleles producing them) Selection sees individuals' traits; allele frequencies change as a consequence over generations.

Darwin's finches on the Galápagos Islands illustrate

Answer: Adaptive radiation: a single ancestral species diversified into 14 species filling different niches (different beak shapes for different food) Different islands and food sources selected for different beak morphologies; allopatric speciation followed by adaptive radiation.

AP Biology · Topic 7.2

Natural Selection Practice

Part of Natural Selection.(EVO-1.B)

Practice questions

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Sample questions

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Sample 1difficulty 2/5
$In evolutionary biology, "fitness" refers to$
- A
  $An individual's lifespan and longevity, contributing offspring numbers to the next generation$
- B
  $An individual's ability to survive and reproduce, contributing alleles to the next generation$
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- C
  $An individual's body size and condition, contributing energy reserves to the next generation$
- D
  $An individual's physical strength and stamina, contributing to dominance in the next generation$
Why
$Fitness measures reproductive success — passing genes on. A weaker organism with more offspring has higher fitness than a stronger one with none.$
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Sample 2difficulty 2/5
$Natural selection acts directly on$
- A
  $Genotypes (and indirectly on the phenotypes they produce)$
- B
  $DNA sequences (and indirectly on the proteins they encode)$
- C
  $Phenotypes (and indirectly on the alleles producing them)$
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- D
  $Mutation rates (and indirectly on the alleles being generated)$
Why
$Selection sees individuals' traits; allele frequencies change as a consequence over generations.$
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Sample 3difficulty 2/5
$Darwin's finches on the Galápagos Islands illustrate$
- A
  $Adaptive radiation: a single ancestral species diversified into ~14 species filling different niches (different beak shapes for different food)$
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- B
  $Genetic drift alone: random fluctuations in small isolated populations, without selection on diet, produced the full range of beak shapes seen across the islands$
- C
  $Hybridization: several distinct mainland species repeatedly interbred on the islands, producing a continuous gradient of beak shapes rather than discrete species$
- D
  $Convergent evolution: unrelated finch-like lineages independently colonized each island and evolved similar beak shapes for similar foods (no shared finch ancestor)$
Why
$Different islands and food sources selected for different beak morphologies; allopatric speciation followed by adaptive radiation.$
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Sample 4difficulty 2/5
$Antibiotic resistance in bacteria is a striking example of$
- A
  $Natural selection in action — resistant strains survive and reproduce in the presence of the drug$
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- B
  $Directed mutation — bacteria deliberately mutate target genes in response to drug presence$
- C
  $Spontaneous adaptation — bacteria modify their cell walls in real time to repel the drug$
- D
  $Lamarckian inheritance — bacteria acquire resistance from drug exposure and pass it to offspring$
Why
$Pre-existing resistant mutants are selected for in the presence of antibiotics. Over time, resistant strains dominate.$
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Sample 5difficulty 2/5
$Most new mutations are$
- A
  $Neutral or slightly deleterious$
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- B
  $Always dominant or recessive$
- C
  $Strongly beneficial or adaptive$
- D
  $Always lethal or strongly harmful$
Why
$The majority of mutations have no phenotypic effect or are mildly deleterious; rare beneficial mutations drive adaptive evolution.$
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