Evolution, Ancestry & Biodiversity — Chapter Practice, Grade 10

Explain population change and branching ancestry using independent evidence.

Problem 1

What is the ultimate source of the new heritable variation that natural selection acts upon?
  1. An organism's conscious effort to change
  2. The environment directly rewriting an organism's genes as needed
  3. Mutation (with reshuffling of genes in sexual reproduction)
  4. Traits organisms build up through exercise and practice
Answer and explanation

Mutation (with reshuffling of genes in sexual reproduction)

New alleles arise from random mutation; sexual reproduction then reshuffles this variation. Natural selection can only act on variation that already exists.

Problem 2

In evolutionary biology, an individual's 'fitness' is best measured by its
  1. physical strength
  2. body size
  3. lifespan
  4. number of surviving, fertile offspring
Answer and explanation

number of surviving, fertile offspring

Fitness means reproductive success — how many surviving, fertile offspring an individual leaves relative to others — not strength, size, or longevity.

Problem 3

List and briefly explain the four factors that together drive natural selection.
Answer and explanation

(1) Heritable variation: individuals differ in traits that can be passed to offspring. (2) Overproduction: populations make more offspring than can survive. (3) Competition: individuals compete for limited resources. (4) Differential survival and reproduction: individuals with traits better suited to the environment survive and reproduce more, so those traits become more common over generations.

Problem 4

A student says, 'Cheetahs run fast because their ancestors kept stretching their legs to run faster and passed that on.' What is wrong with this explanation?
  1. Traits gained during an individual's life aren't inherited; instead, cheetahs born with heritable variation for faster running left more offspring
  2. Nothing — practicing a skill changes the genes you pass to your offspring
  3. Cheetahs consciously decided as a group to evolve speed
  4. Speed is not a heritable trait, so selection cannot affect it
Answer and explanation

Traits gained during an individual's life aren't inherited; instead, cheetahs born with heritable variation for faster running left more offspring

This is the Lamarckian misconception. Natural selection acts on heritable variation that already exists: faster-born cheetahs survived and reproduced more, so speed became more common — individuals do not evolve on purpose.

Problem 5

A population of 500 beetles is 20% dark-colored and 80% light-colored. On dark bark, all of the dark beetles survive a wave of bird predation, but only half of the light beetles survive. How many beetles survive in total?
Answer and explanation

300 beetles

Dark: 500 x 0.20 = 100, all survive = 100. Light: 500 x 0.80 = 400, half survive = 200. Total = 100 + 200 = 300.

Problem 6

Drought favors birds with a heritable beak form that helps open available seeds. Explain the next-generation change. Explain the reasoning in your own words.
Answer and explanation

Selection can shift the population distribution; birds did not change beaks by deciding to adapt.

Birds with that form leave more offspring under these conditions.

Inheritance can increase the form's frequency across generations.

Response criteria

  • Use the stated conditions.
  • Show the evidence or calculation.
  • Explain the conclusion and any stated limitation.

Problem 7

A heritable trait improves reproduction only in a cold environment. Is its fitness advantage universal? Show the reasoning, not just the conclusion.
Hints

Resistance can also spread through gene transfer; the scenario alone does not specify every mechanism.

Answer and explanation

No. Fitness is environment-dependent; the advantage may change elsewhere.

Problem 8

Why must a trait be heritable for selection to predict a sustained inherited population change?
Hints

State what the supplied observations or conditions establish, and separate that from any assumption.

Answer and explanation

Reproductive differences must be transmitted to descendants for the relevant variant frequency to change across generations.

Problem 9

Variation arises and is sorted through different processesVariation arises and is sorted through different processesMutation: can supply new sequence variantsInheritance / recombination: transmit and rearrange variantsSelection: sorts contributions under current conditionsThese processes have different roles; a need does not target a helpful mutation.
Original process-role diagram, not a mutation-rate model or exhaustive population-genetic equation.
Interpret the supplied visual. Does observing a useful new allele prove that need caused that precise mutation?
Answer and explanation

No. Its origin and later contribution are distinct questions; utility after selection does not establish purposeful mutation.

A mutation changes sequence; recombination rearranges existing material; inheritance transmits it. Selection concerns differential contribution among variants under conditions, not the purposeful creation of a helpful change. Some mutation processes have biases, yet this does not mean a population reliably generates exactly the trait it needs. Drift and migration also change frequencies. A changed frequency supports an evolutionary observation, while identifying its cause requires suitable comparisons and evidence of reproductive differences or other mechanisms.

No. Its origin and later contribution are distinct questions; utility after selection does not establish purposeful mutation.

Response criteria

  • Read the structures, axes, directions and units correctly.
  • Connect the evidence with the biological mechanism.
  • Respect stated model assumptions and distinguish an observation from a further inference.

Problem 10

Equal groups of 20 parents of two heritable variants produce 40 and 70 surviving reproductive offspring under one condition. Compare per-parent output and explain why this does not prove a universal advantage.
Answer and explanation

Outputs are 2 and 3.5 offspring per parent; the second is 1.75 times the first here. Other environments, starting frequencies and interactions can change the result, so the advantage is conditional.

Outputs are 2 and 3.5 offspring per parent; the second is 1.75 times the first here. Other environments, starting frequencies and interactions can change the result, so the advantage is conditional.

Response criteria

  • Use the stated measurements or conditions, with correct units.
  • Connect the result to the biological mechanism or evidence relationship.
  • Identify the assumption, model limit or further evidence requested.

Problem 11

The matching bone arrangement in a human arm, a bat wing, and a whale flipper is an example of homologous structures, which are evidence of
  1. a total absence of any evolutionary relationship
  2. descent from a common ancestor
  3. convergent evolution from unrelated ancestors
  4. traits acquired during life
Answer and explanation

descent from a common ancestor

Homologous structures share an underlying anatomical plan because the species inherited it from a common ancestor, even though the structures now serve different functions.

Problem 12

Which of the following is an example of molecular evidence for evolution?
  1. Humans and chimpanzees share about 98-99% of their DNA sequence
  2. A bat wing and a bird wing both allow flight
  3. Fossils in deeper rock layers are older
  4. Kangaroos are found mainly in Australia
Answer and explanation

Humans and chimpanzees share about 98-99% of their DNA sequence

Molecular evidence compares DNA, RNA, or protein sequences. High DNA similarity indicates a recent common ancestor. The other choices are anatomical, fossil, and biogeographic evidence.

Problem 13

Explain the difference between homologous and analogous structures, and state which one is evidence of common ancestry.
Answer and explanation

Homologous structures share the same underlying anatomical plan because of a common ancestor, even if they now have different functions (like a human arm and a bat wing). Analogous structures share only a function and are built differently (like a bird wing and an insect wing), arising from convergent evolution. Only homologous structures are evidence of common ancestry.

Problem 14

Australia is home to many marsupial mammals (like kangaroos and koalas) that are found almost nowhere else. This pattern is best explained by which line of evidence for evolution?
  1. Vestigial structures
  2. Comparative embryology
  3. Biogeography — Australia's long isolation let its mammals diverge separately from those on other continents
  4. The universal genetic code
Answer and explanation

Biogeography — Australia's long isolation let its mammals diverge separately from those on other continents

Biogeography examines how species are distributed. Australia's tens of millions of years of isolation allowed its marsupials to diversify separately, which is why they are found there and almost nowhere else.

Problem 15

Using a simplified molecular clock, scientists estimate that each amino-acid difference between two species' versions of a certain protein represents about 5 million years since they diverged. If two species' versions of the protein differ by 8 amino acids, about how many million years ago did they last share a common ancestor?
Answer and explanation

40 million years

8 differences x 5 million years per difference = 40 million years.

Problem 16

A bat wing and human arm share an underlying bone pattern but differ in function. What inference fits? Explain the reasoning in your own words.
Answer and explanation

The pattern supports common ancestry, with other evidence strengthening the relationship.

The corresponding skeletal arrangement is a homologous pattern.

Inherited modification can produce different functions from a shared structure.

Response criteria

  • Use the stated conditions.
  • Show the evidence or calculation.
  • Explain the conclusion and any stated limitation.

Problem 17

Why do shared molecular sequence patterns support common ancestry? Show the reasoning, not just the conclusion.
Hints

Use multiple characters rather than one superficial similarity.

Answer and explanation

Inheritance explains nested shared features; compare many positions and alternative explanations.

Problem 18

A fossil gap occurs in a sequence. Does it prove no evolution occurred?
Hints

State what the supplied observations or conditions establish, and separate that from any assumption.

Answer and explanation

No. Preservation and sampling are incomplete; evaluate all available evidence and the model's predictions.

Problem 19

Molecular comparisons require matched characters and appropriate modelsMolecular comparisons require matched characters and appropriate modelsTaxon A: ATGCATTaxon B: ATGCACTaxon C: ATTGGCCount differences at matched positions and test more than one region.Sequence similarity constrains a relationship; it is not a complete genealogy.
Original short illustrative sequences, not genomic data from named taxa or a calibrated molecular clock.
Interpret the supplied visual. Could one short matching sequence establish an exact divergence date?
Answer and explanation

No. Dating requires appropriate models, rates/calibration, more evidence and uncertainty, not just a match.

An alignment places corresponding sequence positions for comparison. Differences can reflect mutation, shared history and other processes, while different regions evolve under different constraints and rates. A short sequence match alone can arise by chance or be insufficiently informative. Compare suitable homologous sequences, account for uncertainty and test multiple independent regions when possible. Shared derived patterns can support relationships, but a simple difference count does not directly give elapsed time without a calibrated model and assumptions.

No. Dating requires appropriate models, rates/calibration, more evidence and uncertainty, not just a match.

Response criteria

  • Read the structures, axes, directions and units correctly.
  • Connect the evidence with the biological mechanism.
  • Respect stated model assumptions and distinguish an observation from a further inference.

Problem 20

Two organisms have similar flight function but different structural/developmental details, while other sequences support separate lineages. Explain how convergence differs from evidence of close ancestry.
Answer and explanation

Similar selection pressures can produce analogous functional resemblance through convergence. Close ancestry requires appropriate shared derived/homologous evidence, supported by independent records; function alone does not settle it.

Similar selection pressures can produce analogous functional resemblance through convergence. Close ancestry requires appropriate shared derived/homologous evidence, supported by independent records; function alone does not settle it.

Response criteria

  • Use the stated measurements or conditions, with correct units.
  • Connect the result to the biological mechanism or evidence relationship.
  • Identify the assumption, model limit or further evidence requested.

Problem 21

What is the ultimate source of all new alleles in a population's gene pool?
  1. Gene flow
  2. Genetic drift
  3. Natural selection
  4. Mutation
Answer and explanation

Mutation

Mutation is the only mechanism that creates entirely new alleles. Gene flow, drift, and selection can only shuffle, spread, or remove variation that mutation first produced.

Problem 22

Genetic drift has its strongest effect in
  1. small populations
  2. very large populations
  3. populations with high gene flow
  4. populations under strong natural selection
Answer and explanation

small populations

Drift is random change in allele frequencies. In small populations, chance events (like which few individuals happen to reproduce) can swing allele frequencies dramatically; in large populations these chance effects average out.

Problem 23

Explain why gene flow between two populations tends to work against speciation, while reproductive isolation allows it to happen.
Answer and explanation

Gene flow moves alleles between populations and keeps their gene pools mixed and similar, so they can't diverge into separate species. Reproductive isolation stops that exchange of genes, letting mutation, drift, and selection push each population's gene pool in its own direction until they become separate species.

Problem 24

A few birds are blown by a storm to a remote island and start a new population whose allele frequencies differ from the mainland's just by chance. This is an example of
  1. a prezygotic reproductive barrier
  2. the founder effect (a form of genetic drift)
  3. gene flow between the island and mainland
  4. natural selection favoring island traits
Answer and explanation

the founder effect (a form of genetic drift)

A small group founding a new population carries only a random sample of the original gene pool, so its allele frequencies differ by chance. This is the founder effect, a type of genetic drift.

Problem 25

A population of 800 individuals has the A allele at a frequency of 0.25. A bottleneck event reduces the population to just 40 survivors, and by chance the A allele frequency in the survivors is now 0.60. Each individual is diploid and carries 2 copies of the gene. How many copies of the A allele are present in the 40 survivors?
Answer and explanation

48 copies

40 survivors x 2 copies each = 80 total gene copies. 0.60 x 80 = 48 copies of the A allele.

Problem 26

A random storm kills most of a small population regardless of genotype. Survivor allele frequencies differ. Identify a likely mechanism. Explain the reasoning in your own words.
Answer and explanation

Genetic drift through a bottleneck is consistent with the scenario.

Survival in the prompt is unrelated to the allele's benefit.

A small survivor sample can differ by chance.

Response criteria

  • Use the stated conditions.
  • Show the evidence or calculation.
  • Explain the conclusion and any stated limitation.

Problem 27

A few individuals migrate and reproduce in another population. What process transfers their alleles? Show the reasoning, not just the conclusion.
Hints

Random sampling differs from trait-dependent reproductive success.

Answer and explanation

Gene flow.

Problem 28

Why does a geographic barrier not automatically create a new species?
Hints

State what the supplied observations or conditions establish, and separate that from any assumption.

Answer and explanation

Reproductive isolation and divergence must be established; separation alone does not guarantee them.

Problem 29

A bottleneck can change frequencies through chance samplingA bottleneck can change frequencies through chance samplingSource sample: 18 blue / 6 goldChance survivors: 3 / 3Random sampling can change frequency without a fitness difference.
Original chance-survivor example with selected representatives, not a real event or exact expected drift trajectory.
Interpret the supplied visual. Does the gold fraction increase prove gold individuals were better adapted?
Answer and explanation

No. The stated random sampling can change frequency without a fitness difference; mechanism evidence is needed.

Genetic drift is chance change in allele frequencies associated with finite reproductive sampling. A bottleneck sharply reduces population size; a founder effect concerns a small group establishing a new population. Random loss can alter representation and remove variants without proving a selective advantage. Drift can occur alongside selection and gene flow. The source gold fraction here is 6/24=1/4, while the selected survivor sample is 3/6=1/2. This example illustrates a possible outcome, not a required direction for all bottlenecks.

No. The stated random sampling can change frequency without a fitness difference; mechanism evidence is needed.

Response criteria

  • Read the structures, axes, directions and units correctly.
  • Connect the evidence with the biological mechanism.
  • Respect stated model assumptions and distinguish an observation from a further inference.

Problem 30

A source population has 70 blue and 30 gold representatives. A stated random founder group has 2 blue and 3 gold. Compare gold fractions and explain what the change does not establish.
Answer and explanation

The source fraction is 30%, the founder fraction 60%. A random sample can yield that change; it does not alone demonstrate gold advantage, new mutation or completed speciation.

The source fraction is 30%, the founder fraction 60%. A random sample can yield that change; it does not alone demonstrate gold advantage, new mutation or completed speciation.

Response criteria

  • Use the stated measurements or conditions, with correct units.
  • Connect the result to the biological mechanism or evidence relationship.
  • Identify the assumption, model limit or further evidence requested.

Problem 31

In binomial nomenclature, an organism's two-part scientific name is made of its
  1. domain and kingdom
  2. family and order
  3. genus and species
  4. kingdom and phylum
Answer and explanation

genus and species

Binomial ('two-name') nomenclature combines the genus (first, capitalized) and the species (second), as in Homo sapiens.

Problem 32

The three domains into which all life is classified are
  1. Plants, Animals, and Fungi
  2. Producers, Consumers, and Decomposers
  3. Prokaryotes, Protists, and Vertebrates
  4. Bacteria, Archaea, and Eukarya
Answer and explanation

Bacteria, Archaea, and Eukarya

Based on Carl Woese's molecular work, all life is divided into three domains: Bacteria, Archaea, and Eukarya (which contains all organisms with complex cells).

Problem 33

Explain what a shared derived trait is and how it helps you group organisms on a cladogram.
Answer and explanation

A shared derived trait is a feature that first evolved in a common ancestor and was inherited by all of its descendants. On a cladogram, all the organisms that share that trait form a group (clade) branching from that ancestor, so shared derived traits let you identify which organisms are more closely related.

Problem 34

On a cladogram, salamanders and turtles branch from a common ancestor that is more recent than the ancestor either shares with sharks. What can you conclude?
  1. Salamanders and turtles are more closely related to each other than either is to sharks
  2. Sharks are more closely related to turtles than salamanders are
  3. All three are equally related
  4. Branch points on a cladogram carry no information about relatedness
Answer and explanation

Salamanders and turtles are more closely related to each other than either is to sharks

A more recent shared branch point means a closer relationship, so salamanders and turtles are more closely related to each other than either is to sharks.

Problem 35

A region originally had 800 native species. Habitat loss has driven 120 of them to extinction. What percentage of the region's native species has been lost?
Answer and explanation

15 %

120 / 800 = 0.15 = 15%.

Problem 36

Two communities each contain five species, but one is dominated by a single species. Are their diversity patterns identical? Explain the reasoning in your own words.
Answer and explanation

No; equal richness does not establish equal biodiversity patterns.

Species richness matches at five.

Relative abundances differ, so evenness and ecological structure can differ.

Response criteria

  • Use the stated conditions.
  • Show the evidence or calculation.
  • Explain the conclusion and any stated limitation.

Problem 37

Why can a classification change after DNA evidence is added? Show the reasoning, not just the conclusion.
Hints

State which measure is being compared.

Answer and explanation

New evidence can revise the inferred evolutionary relationships represented by groups.

Problem 38

Can a local identification key classify every species worldwide?
Hints

State what the supplied observations or conditions establish, and separate that from any assumption.

Answer and explanation

No. Its choices and species coverage are limited to its intended scope.

Problem 39

A key identifies a specimen within its stated scopeA key identifies a specimen within its stated scopeFeature present?Follow defined option AFollow defined option BAn identification key is a decision tool, not an ancestry timeline.
Original paired-choice tool, not a field key for handling unknown organisms.
Interpret the supplied visual. Does arriving at the same key choice prove two organisms are closest evolutionary relatives?
Answer and explanation

No. A key sorts using selected identifying traits; ancestry requires appropriate relationship evidence.

A dichotomous key offers paired choices using defined characters. Reliable use requires visible or measured features, applicable life stage and the set of organisms the key covers. A wrong early choice can send the user to a plausible-looking wrong endpoint. Identification differs from an ancestry explanation: a practical key can use conspicuous traits without turning every choice into an evolutionary branching event. Report uncertainty when a specimen lacks a required feature or falls outside the key’s scope.

No. A key sorts using selected identifying traits; ancestry requires appropriate relationship evidence.

Response criteria

  • Read the structures, axes, directions and units correctly.
  • Connect the evidence with the biological mechanism.
  • Respect stated model assumptions and distinguish an observation from a further inference.

Problem 40

Two equal-effort samples each contain five species. Counts are 8,8,8,8,8 versus 36,1,1,1,1. Compare richness and evenness and name one sampling limitation.
Answer and explanation

Both have richness five and total 40, but the first is more even. Detection, area, timing and effort can affect observed richness; unobserved species are not automatically absent.

Both have richness five and total 40, but the first is more even. Detection, area, timing and effort can affect observed richness; unobserved species are not automatically absent.

Response criteria

  • Use the stated measurements or conditions, with correct units.
  • Connect the result to the biological mechanism or evidence relationship.
  • Identify the assumption, model limit or further evidence requested.

Problem 41

On ((A,B),C), which are sister lineages?
  1. A and B
  2. A and C
  3. B and C
  4. Every pair equally
Answer and explanation

A and B

A and B share the most recent node.

Problem 42

Why should an unlabeled branch length not be read as time?
Answer and explanation

The diagram has not defined a time scale; length may be purely a layout choice.

Problem 43

Why can a shared function fail to show closest ancestry?
Answer and explanation

Similar functions can evolve independently; multiple traits and sequence evidence help test relationships.

Problem 44

In a tree, A and B share a recent node; C joins their branch at an older node. Which pair is most closely related? Explain the reasoning in your own words.
Answer and explanation

A and B are the closest pair in the supplied tree.

Trace the shared ancestors rather than the page spacing.

A and B share the most recent node.

Response criteria

  • Use the stated conditions.
  • Show the evidence or calculation.
  • Explain the conclusion and any stated limitation.

Problem 45

If branches rotate around a node, does common ancestry change? Show the reasoning, not just the conclusion.
Hints

A tree's topology carries relatedness; lengths need a declared scale.

Answer and explanation

No. The same branching connections remain.

Problem 46

Without a time scale, can a long branch be assumed to mean twice as many years?
Hints

State what the supplied observations or conditions establish, and separate that from any assumption.

Answer and explanation

No. Branch length represents time only when the diagram specifies that convention and scale.

Problem 47

A relationship tree does not imply an unstated time scaleA relationship tree does not imply an unstated time scaleABCNo time scale shownNo “progress” rankingNo ancestral tip assumedOnly specified branch metrics can support distance or time comparisons.
Original unscaled cladogram; distances and node positions are intentionally not numerical age evidence.
Interpret the supplied visual. Can this arbitrary-length tree tell when A and B diverged?
Answer and explanation

No. A dated or otherwise calibrated model and uncertainty are needed; topology alone supplies relative relationships.

A branch metric may represent elapsed time, genetic change or another quantity when explicitly defined. Many classroom cladograms show topology only, so drawn horizontal distance cannot establish divergence dates or which lineage changed fastest. Missing lineages and unresolved nodes also limit interpretation. A long branch on an unscaled diagram is not evidence of greater complexity, age or survival value. Read the legend, rooting and sampling before attempting any quantitative relationship comparison.

No. A dated or otherwise calibrated model and uncertainty are needed; topology alone supplies relative relationships.

Response criteria

  • Read the structures, axes, directions and units correctly.
  • Connect the evidence with the biological mechanism.
  • Respect stated model assumptions and distinguish an observation from a further inference.

Problem 48

A rooted tree has topology ((A,B),C). A drawing is rotated to show B first, then A, then C. State the relationship and explain what is needed to estimate divergence time.
Answer and explanation

A and B remain sister lineages in that topology. Tip order does not alter their shared ancestor; time estimation needs a specified calibrated branch metric/model and uncertainty.

A and B remain sister lineages in that topology. Tip order does not alter their shared ancestor; time estimation needs a specified calibrated branch metric/model and uncertainty.

Response criteria

  • Use the stated measurements or conditions, with correct units.
  • Connect the result to the biological mechanism or evidence relationship.
  • Identify the assumption, model limit or further evidence requested.

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