Natural Selection, Adaptation & Population Change — Practice · Grade 7 Science

Chapter: Evolution, Evidence & Life History

What this practice covers

By the end of Natural Selection, Adaptation & Population Change you should be able to:

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

Vocabulary used: natural selection, adaptation, fitness, frequency, heritable variation.

Problem 1

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 2

Is one color universally the fittest?
Answer and explanation

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

Problem 3

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 4

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 5

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 6

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 7

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 8

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

30 %

18/60×100=30%.

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