Natural Selection — Practice · Grade 10 Science

Chapter: Evolution, Ancestry & Biodiversity

What this practice covers

By the end of Natural Selection you should be able to:

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

Vocabulary used: natural selection, variation, overproduction, fitness, adaptation, selective pressure.

Problem 1

What is the ultimate source of the new heritable variation that natural selection acts upon?
  1. An organism's conscious effort to change
  2. The environment directly rewriting an organism's genes as needed
  3. Mutation (with reshuffling of genes in sexual reproduction)
  4. Traits organisms build up through exercise and practice
Answer and explanation

Mutation (with reshuffling of genes in sexual reproduction)

New alleles arise from random mutation; sexual reproduction then reshuffles this variation. Natural selection can only act on variation that already exists.

Problem 2

In evolutionary biology, an individual's 'fitness' is best measured by its
  1. physical strength
  2. body size
  3. lifespan
  4. number of surviving, fertile offspring
Answer and explanation

number of surviving, fertile offspring

Fitness means reproductive success — how many surviving, fertile offspring an individual leaves relative to others — not strength, size, or longevity.

Problem 3

List and briefly explain the four factors that together drive natural selection.
Answer and explanation

(1) Heritable variation: individuals differ in traits that can be passed to offspring. (2) Overproduction: populations make more offspring than can survive. (3) Competition: individuals compete for limited resources. (4) Differential survival and reproduction: individuals with traits better suited to the environment survive and reproduce more, so those traits become more common over generations.

Problem 4

A student says, 'Cheetahs run fast because their ancestors kept stretching their legs to run faster and passed that on.' What is wrong with this explanation?
  1. Traits gained during an individual's life aren't inherited; instead, cheetahs born with heritable variation for faster running left more offspring
  2. Nothing — practicing a skill changes the genes you pass to your offspring
  3. Cheetahs consciously decided as a group to evolve speed
  4. Speed is not a heritable trait, so selection cannot affect it
Answer and explanation

Traits gained during an individual's life aren't inherited; instead, cheetahs born with heritable variation for faster running left more offspring

This is the Lamarckian misconception. Natural selection acts on heritable variation that already exists: faster-born cheetahs survived and reproduced more, so speed became more common — individuals do not evolve on purpose.

Problem 5

A population of 500 beetles is 20% dark-colored and 80% light-colored. On dark bark, all of the dark beetles survive a wave of bird predation, but only half of the light beetles survive. How many beetles survive in total?
Answer and explanation

300 beetles

Dark: 500 x 0.20 = 100, all survive = 100. Light: 500 x 0.80 = 400, half survive = 200. Total = 100 + 200 = 300.

Problem 6

Drought favors birds with a heritable beak form that helps open available seeds. Explain the next-generation change. Explain the reasoning in your own words.
Answer and explanation

Selection can shift the population distribution; birds did not change beaks by deciding to adapt.

Birds with that form leave more offspring under these conditions.

Inheritance can increase the form's frequency across generations.

Response criteria

  • Use the stated conditions.
  • Show the evidence or calculation.
  • Explain the conclusion and any stated limitation.

Problem 7

A heritable trait improves reproduction only in a cold environment. Is its fitness advantage universal? Show the reasoning, not just the conclusion.
Hints

Resistance can also spread through gene transfer; the scenario alone does not specify every mechanism.

Answer and explanation

No. Fitness is environment-dependent; the advantage may change elsewhere.

Problem 8

Why must a trait be heritable for selection to predict a sustained inherited population change?
Hints

State what the supplied observations or conditions establish, and separate that from any assumption.

Answer and explanation

Reproductive differences must be transmitted to descendants for the relevant variant frequency to change across generations.

Problem 9

Variation arises and is sorted through different processesVariation arises and is sorted through different processesMutation: can supply new sequence variantsInheritance / recombination: transmit and rearrange variantsSelection: sorts contributions under current conditionsThese processes have different roles; a need does not target a helpful mutation.
Original process-role diagram, not a mutation-rate model or exhaustive population-genetic equation.
Interpret the supplied visual. Does observing a useful new allele prove that need caused that precise mutation?
Answer and explanation

No. Its origin and later contribution are distinct questions; utility after selection does not establish purposeful mutation.

A mutation changes sequence; recombination rearranges existing material; inheritance transmits it. Selection concerns differential contribution among variants under conditions, not the purposeful creation of a helpful change. Some mutation processes have biases, yet this does not mean a population reliably generates exactly the trait it needs. Drift and migration also change frequencies. A changed frequency supports an evolutionary observation, while identifying its cause requires suitable comparisons and evidence of reproductive differences or other mechanisms.

No. Its origin and later contribution are distinct questions; utility after selection does not establish purposeful mutation.

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

Equal groups of 20 parents of two heritable variants produce 40 and 70 surviving reproductive offspring under one condition. Compare per-parent output and explain why this does not prove a universal advantage.
Answer and explanation

Outputs are 2 and 3.5 offspring per parent; the second is 1.75 times the first here. Other environments, starting frequencies and interactions can change the result, so the advantage is conditional.

Outputs are 2 and 3.5 offspring per parent; the second is 1.75 times the first here. Other environments, starting frequencies and interactions can change the result, so the advantage is conditional.

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.

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