How Natural Selection Works · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

How Natural Selection Works

Science · Ecosystems & Habitats · ages 12-14
Name ______________________   Date ____________

  1. In natural selection, an organism can choose to develop a trait it needs.

    Circle one:   True   False

  2. Which of these can allow evolution by natural selection?

    • Heritable variation between individuals
    • An organism wanting to change
    • Every individual in the population staying identical

  3. Which term names the mechanism in which individuals with a helpful inherited trait leave more offspring than others?

    • Natural selection
    • Evolution
    • Mutation

  4. Wolves hunt rabbits. An inherited speed trait helps some rabbits escape more often, with no other survival or breeding disadvantage. Why could faster rabbits become more common?

    • Faster rabbits survive longer and pass the trait to more offspring
    • Wolves prefer to only hunt slow-looking rabbits on purpose
    • Fast rabbits change their babies' running speed after they are born

  5. During the Industrial Revolution, dark-colored peppered moths became more common on sooty, polluted trees. What is the best explanation?

    • Moths changed color on purpose to hide from birds
    • Dark moths existed; soot made pale moths easier to spot
    • Birds only ate dark moths, which caused light moths to increase

  6. An antibiotic kills all but 2 resistant bacteria. After two rounds of cell division, each survivor has 4 descendants with the resistance gene. How many resistant descendants are there?

    Answer: ______________

  7. Trees have inherited differences in leaf size. Resources are plentiful, and every leaf size has equal survival and reproductive success. Will natural selection favour one leaf size under these conditions?

    • Yes, because the trees will choose the best leaf size
    • Yes, because there is variation and heredity
    • No, all leaf sizes have equal reproductive success

  8. A student says: 'Natural selection and evolution are the same thing happening at the same time.' What is the best correction?

    • They're right, the two terms mean the same process
    • Selection is one cause of evolutionary change
    • Evolution happens first, and it causes natural selection afterward
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Answer key

For grown-ups. Fold this page away before handing over the rest.

How Natural Selection Works W1-mt_FuVEZ1Ac9s-s1

  1. False · Bacteria do not develop a needed trait by choice. Selection acts on variants that happen to be present.
  2. Heritable variation between individuals · Heritable variation gives selection differences to act on. Traits associated with more offspring can become more common.
  3. Natural selection · Natural selection is the mechanism of unequal reproductive success associated with inherited traits.
  4. Faster rabbits survive longer and pass the trait to more offspring · Surviving longer means more chances to reproduce. Because the speed trait is heritable, more of the next generation inherits it.
  5. Dark moths existed; soot made pale moths easier to spot · The mutation for dark color already existed. Pollution changed which color survived: light moths stood out on sooty bark and got eaten more, so dark moths left more offspring.
  6. 8 · There are 2 surviving lineages, with 4 descendants each: 2 × 4 = 8 resistant descendants.
  7. No, all leaf sizes have equal reproductive success · The premise gives no survival or reproductive advantage to any leaf size. Selection does not favour one, though drift could still change their frequencies.
  8. Selection is one cause of evolutionary change · Natural selection is one mechanism that changes inherited variation. Evolution can also result from mutation, gene flow, or genetic drift.
Worksheet · LightMySky