Evidence for Evolution — Drills · Grade 10 Science

Chapter: Evolution, Ancestry & Biodiversity

What these drills covers

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

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

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

Problem 1

Homologous structures are structures that
  1. perform the same function in unrelated species
  2. share a common underlying structure and ancestry, whatever their current function
  3. are always vestigial
  4. have identical DNA
Answer and explanation

share a common underlying structure and ancestry, whatever their current function

Homologous structures share an inherited underlying plan — the limb bones of mammals, for instance — even when their functions differ.

Problem 2

The wing of a bird and the wing of an insect are similar in function but differ entirely in structure and ancestry. These are
  1. homologous structures
  2. analogous structures
  3. vestigial structures
  4. identical structures
Answer and explanation

analogous structures

Analogous structures arise independently for similar functions, so similarity of function alone is not evidence of relatedness.

Problem 3

A protein differs from the human version by 1 amino acid in one species and 32 in another. Based on molecular similarity alone, how many times more differences does the second species show?
Answer and explanation

32

32 / 1 = 32 times as many differences, suggesting a more distant common ancestor, provided the rate of change is comparable.

Problem 4

Fossils in undisturbed sedimentary rock layers are useful because
  1. all fossils are the same age
  2. deeper layers are generally older, giving a sequence
  3. fossils form from any organism equally
  4. they record behaviour directly
Answer and explanation

deeper layers are generally older, giving a sequence

In undisturbed strata, lower layers were deposited earlier, so the vertical order gives a relative time sequence for the fossils they contain.

Problem 5

Explain why several independent lines of evidence make a stronger case than any single line.
Answer and explanation

Each line of evidence has its own weaknesses: the fossil record is incomplete, structural similarity can arise independently, and molecular comparisons depend on assumptions about rates of change. When fossil sequences, anatomical homologies, embryological similarities, molecular comparisons, and biogeography point to the same relationships, a single alternative explanation would have to account for all of them at once, which is far harder. Agreement among methods with different weaknesses is what makes the conclusion robust.

Response criteria

  • State a biologically accurate conclusion.
  • Show the data, mechanism, or calculation that supports it.
  • Include units, conditions, or limits where relevant.

Problem 6

Why is the fossil record described as incomplete, and what does that imply about arguments from missing fossils?
Answer and explanation

Fossilization requires particular conditions — rapid burial in sediment, usually of hard parts — so most organisms leave no fossil, and many fossils that formed have since been destroyed or lie unexposed. The record therefore samples the past unevenly. An absence of fossils for a group or an interval is weak evidence that it did not exist, because non-preservation and non-discovery both produce the same absence.

Response criteria

  • State a biologically accurate conclusion.
  • Show the data, mechanism, or calculation that supports it.
  • Include units, conditions, or limits where relevant.

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