Evolution, Evidence & Life History — Chapter Practice, Grade 7

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

Problem 1

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 2

Does the relative order give exact years?
Answer and explanation

No. It gives an older-younger relationship under the assumptions; numerical ages need additional dating evidence.

Problem 3

Why can fossil absence be uncertain?
Answer and explanation

Preservation, exposure, and sampling vary, so an organism may leave no detected record.

Problem 4

Why is “newer means more perfect” not a scientific conclusion?
Answer and explanation

Perfection is not a defined biological measure, and evolution involves branching and context-dependent traits rather than one universal ranking.

Problem 5

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 6

A real layer sequence is overturned. Can its present bottom automatically be called oldest?
Answer and explanation

No. The simple rule assumed upright undisturbed deposition. Investigate the geological history before assigning order.

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 7

Which is trace evidence?
  1. A preserved footprint
  2. A graph axis
  3. A fictional budget
  4. A lens factor
Answer and explanation

A preserved footprint

A footprint records activity rather than preserving the whole body.

Problem 8

Why does one fossil collection not inventory every species that lived?
Answer and explanation

Preservation and exposure vary, and collections sample limited places and materials. Many organisms leave no detected fossil in that collection.

Problem 9

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 10

Is one color universally the fittest?
Answer and explanation

No. Advantage depends on conditions and effects on reproductive success.

Problem 11

Why use both variant count and total count?
Answer and explanation

The share depends on the denominator; raw counts alone may misrepresent frequency change.

Problem 12

Does a small frequency change alone prove selection?
Answer and explanation

No. Sampling, movement, and other processes may contribute; evidence about inheritance and reproductive success is needed.

Problem 13

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 14

An individual becomes larger after extra food during one month. Is that alone evidence of natural selection?
Answer and explanation

No. It can be an individual developmental response. Selection requires inherited variation and differing 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 15

Which is required in the stated selection explanation?
  1. Heritable variation and different reproductive success
  2. A wish to evolve
  3. Every individual identical
  4. No generation interval
Answer and explanation

Heritable variation and different reproductive success

Selection connects inherited differences with reproductive outcomes across generations.

Problem 16

A variant occurs in 18 of 60 organisms. Find its observed percentage.
Answer and explanation

30 %

18/60×100=30%.

Problem 17

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 18

Why is “vestigial means no function whatsoever” too strong?
Answer and explanation

Reduced ancestral roles can coexist with remaining or changed functions.

Problem 19

Why is one short sequence an incomplete relationship test?
Answer and explanation

It may not represent the whole history and can be affected by sampling and different rates; additional regions and other evidence help.

Problem 20

Does rotating B and C around their node change their relationship?
Answer and explanation

No. The shared node and connections remain the same; visual left-right order is not the ancestry criterion.

Problem 21

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 22

Two living tips are drawn next to each other but share a deeper ancestor than another pair. Which determines relatedness in the model?
Answer and explanation

Shared branching nodes determine the modeled relationship, not distance between printed tip labels.

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 23

Which determines the represented relationship?
  1. Shared branching nodes
  2. Alphabetical tip order
  3. The prettiest color
  4. Every tip’s horizontal spacing
Answer and explanation

Shared branching nodes

Topology and shared nodes represent relationships; display choices need a stated meaning.

Problem 24

Why combine fossils, anatomy, and genetic evidence?
Answer and explanation

Different observations can test related aspects of a relationship hypothesis. Agreement strengthens it while limitations or contradictions guide further investigation.

Problem 25

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 26

Why compare environments before selecting for size?
Answer and explanation

Resource differences can affect size; without comparable conditions, the chosen characteristic may not reflect an inherited contribution.

Problem 27

Does improvement in one chosen trait prove improvement in every trait?
Answer and explanation

No. Other outcomes and tradeoffs need separate evidence.

Problem 28

Why can a uniform variety be vulnerable to one particular threat?
Answer and explanation

If individuals share a susceptible inherited response, a threat targeting that response can affect many; the actual effect needs evidence.

Problem 29

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 30

Can selecting for an existing trait guarantee a completely new desired trait appears next generation?
Answer and explanation

No. Selection acts on heritable variation and reproductive contribution; new changes are not guaranteed or produced by desire.

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 31

Which comparison better tests an inherited yield contribution?
  1. Parents in entirely different conditions only
  2. Offspring groups under matched conditions with replication
  3. Only the highest one result
  4. A label saying best
Answer and explanation

Offspring groups under matched conditions with replication

Matched offspring comparisons address environmental differences and variability.

Problem 32

A sample has 15 plants with a selected variant among 50. Find the share.
Answer and explanation

30 %

15/50×100=30%, without assuming universal advantage.

Problem 33

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.

Problem 34

Why must the report explain what each source contributes?
Answer and explanation

Different records answer different questions; combining names without connections does not establish the mechanism.

Problem 35

How should an assumed inheritance rule be reported?
Answer and explanation

State it as a supplied model assumption and distinguish it from measured offspring evidence.

Problem 36

What makes a next test useful?
Answer and explanation

It addresses a defined uncertainty or alternative explanation rather than merely repeating an unsupported conclusion.

Problem 37

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 38

A project uses only a graph of frequencies and claims a specific new mutation caused the change. What evidence is missing?
Answer and explanation

The graph does not identify a new sequence change or its transmission. Genetic and reproductive evidence, with alternatives such as movement and sampling considered, would be needed.

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 39

Which improves an inquiry conclusion?
  1. State its evidence and limitation
  2. Omit every assumption
  3. Call one graph universal proof
  4. Copy a model without reading the record
Answer and explanation

State its evidence and limitation

A clear evidence connection and qualification make the conclusion assessable.

Problem 40

A variant share rises from 25% to 40%. Find the increase in percentage points.
Answer and explanation

15 percentage points

40−25=15 percentage points; a relative percent increase is a different calculation.

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