Evidence for Evolution — Practice · Grade 10 Science

Chapter: Evolution, Ancestry & Biodiversity

What this practice covers

By the end of Evidence for Evolution you should be able to:

10 questions, multiple choice, written answer and numeric, each with a worked explanation.

Vocabulary used: homologous structures, analogous structures, vestigial structure, transitional fossil, biogeography, molecular evidence.

Problem 1

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 2

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 3

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 4

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 5

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 6

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 7

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 8

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 9

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 10

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.

Browse all courses