Evolution, Evidence & Life History — Problem set, Grade 7

Five focused units, a three-session investigation, chapter review, and chapter quiz.

Review the key ideas

Fossils, Rock Layers & Life History

Fossils preserve evidence of past life, including remains, impressions, and traces such as tracks. Preservation is uncommon and depends on conditions. Hard parts, rapid burial, and particular environments are often more likely to leave records than soft material exposed to decay. The fossil record is therefore informative and incomplete.

Natural Selection, Adaptation & Population Change

Natural selection can change the frequency of inherited variants across generations when individuals differ in reproductive success related to those variants. Individuals must vary, some variation must be heritable, and conditions must affect outcomes. Merely noticing that survivors differ is not a complete demonstration of an inherited population change.

Common Ancestry, Evidence & Branching Trees

Common ancestry explains inherited similarities among organisms through shared predecessors. Homologous structures share underlying inherited relationships even when functions differ, while similar functions can arise through different histories. A butterfly wing and a bird wing both support flight but do not have the same underlying wing construction.

Selective Breeding & Genetic Diversity

Artificial selection occurs when people influence which organisms reproduce according to desired characteristics. It acts on available heritable variation and reproductive outcomes, while mutations can introduce new variation over time. A desired trait does not appear automatically because a breeder wants it.

Life Science Capstone: Explain, Test & Revise

A life-science inquiry report connects a question, biological mechanism, relevant evidence, calculations or models, and a qualified conclusion. It can draw on cells, inheritance, body systems, or ecosystem relationships without pretending one small dataset answers every topic. Choose a bounded question that can be addressed with the supplied records.

Problem 1

Illustrative upright undisturbed layers: bottom contains Species A; middle A and B; top B. No numerical ages or complete regional survey are supplied. State relative order, describe detected species patterns, and qualify an extinction claim.
Answer and explanation

The bottom layer is relatively oldest and the top youngest under the stated assumptions. A is not detected in the top record, while B occurs in middle and top. This local pattern alone does not prove A became extinct everywhere or supply exact dates. Preservation, sampling, and other locations need consideration.

Order bottom before middle before top.

A is detected in lower two; B in upper two.

Separate local non-detection from global extinction.

Response criteria

  • Explain the relevant biological process accurately.
  • Use the supplied evidence and show calculation steps with units where needed.
  • Connect a labeled model or mechanism with the claim.
  • State an assumption, evidence limitation, or useful next observation.

Problem 2

Can a footprint be a fossil without a preserved body?
Answer and explanation

Yes. It can preserve evidence of an organism’s activity and is a trace fossil.

Problem 3

Illustrative inherited-color model: generation one has 20 dark of 100 beetles; generation two has 50 dark of 100. Dark beetles are harder to detect on the stated ground, and greater reproductive contribution is recorded. Calculate frequencies, explain selection, and state why the evidence is stronger than a color change in one beetle.
Answer and explanation

The dark variant rises from 20% to 50%, a 30-percentage-point increase. The supplied inheritance and reproductive evidence support selection in this model, with visibility as the proposed mechanism. It concerns population proportions across generations, not one individual choosing a new trait. Real studies would also test other changes and sampling limits.

Frequencies are 20% and 50%.

Increase is 30 percentage points.

Connect inherited variation, visibility, and reproductive contribution across generations.

Response criteria

  • Explain the relevant biological process accurately.
  • Use the supplied evidence and show calculation steps with units where needed.
  • Connect a labeled model or mechanism with the claim.
  • State an assumption, evidence limitation, or useful next observation.

Problem 4

Why must inherited variation be specified?
Answer and explanation

A temporary acquired difference may not be passed to offspring, so it cannot support the same across-generation mechanism.

Problem 5

Illustrative tree: A splits from a lineage before B and C split from each other. No times, branch-length scale, or actual species identities are supplied. Identify the closest pair in the model, explain why C need not descend from living B, and state what timing cannot be inferred.
Answer and explanation

B and C share the more recent common ancestor in the stated topology. C is not represented as descending from living B; both connect through an ancestral lineage. Exact dates or elapsed times cannot be inferred because no time scale is supplied. The diagram is a hypothesis whose supporting evidence would need examination.

Find the shared B–C node.

Treat living B and C as tips, not parent and child.

Respect the missing time scale.

Response criteria

  • Explain the relevant biological process accurately.
  • Use the supplied evidence and show calculation steps with units where needed.
  • Connect a labeled model or mechanism with the claim.
  • State an assumption, evidence limitation, or useful next observation.

Problem 6

Does the same function alone prove close ancestry?
Answer and explanation

No. Similar functions can arise through different histories; structural and other evidence must be compared.

Problem 7

Illustrative plants: A averages 12 seeds in favorable soil; B averages 9 in poorer soil. A proposal says breeding only A proves an inherited yield improvement. Explain the confound, propose a stronger comparison, and identify a diversity tradeoff.
Answer and explanation

The observed yield difference does not isolate an inherited advantage because soil differs. Compare parent and offspring performance under suitable matched conditions and independent replicates. Selecting only a narrow group may reduce variation, so measure other outcomes and possible vulnerabilities rather than declaring universal improvement from one trait.

Notice unequal soil conditions.

Compare replicated offspring under matched conditions.

Consider narrowing inherited variation.

Response criteria

  • Explain the relevant biological process accurately.
  • Use the supplied evidence and show calculation steps with units where needed.
  • Connect a labeled model or mechanism with the claim.
  • State an assumption, evidence limitation, or useful next observation.

Problem 8

Does training an individual automatically count as selective breeding?
Answer and explanation

No. Selective breeding changes which organisms reproduce based on traits; training changes an individual’s experience.

Problem 9

Illustrative inherited-seed model: generation one has 30 of 100 plants with Variant A; generation two has 45 of 100. A contributes more surviving offspring under the stated conditions, but movement and other populations were not measured. Calculate the change, explain a selection mechanism, identify an alternative or limit, and propose a next observation.
Answer and explanation

Variant A rises from 30% to 45%, a 15-percentage-point increase. Given the supplied inherited trait and greater surviving-offspring contribution, selection is a supported mechanism in this model. Unmeasured movement or sampling can also affect frequencies. Record reproductive outcomes across more generations and compare movement or matched conditions before generalizing beyond this fictional population.

Find frequencies: 30% and 45%.

Change is 15 percentage points.

Connect inheritance and reproductive contribution; examine movement and other evidence.

Response criteria

  • Explain the relevant biological process accurately.
  • Use the supplied evidence and show calculation steps with units where needed.
  • Connect a labeled model or mechanism with the claim.
  • State an assumption, evidence limitation, or useful next observation.

Problem 10

Why define the population and interval?
Answer and explanation

They determine what the measured change concerns and prevent a local record from becoming a universal claim.

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