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9th grade · Science · Unit 10 of 14

Evidence & Mechanisms of Evolution

Fossils, biogeography and homologies, rates of change, speciation, drift and gene flow.

What your child practices

Practices the evidence for common ancestry (the fossil record, biogeography, and anatomical, molecular and developmental homologies), explanations for different rates of change in the fossil record (gradualism, abrupt appearance, stasis), how natural selection can lead to speciation, and mechanisms other than selection: genetic drift, gene flow, mutation and recombination.

Alabama Course of Study content standard: BIO.13; BIO.14 · evidence of common ancestry and the mechanisms of evolution

How we explain it

Children can open this short lesson before they practice.

  1. Evidence for common ancestry: fossils, biogeography, and anatomical, molecular and developmental homologies.
  2. Gradualism is slow, steady change; punctuated equilibrium is long stability with quick bursts.
  3. Genetic drift, like a bottleneck, changes alleles by chance. Speciation forms a new species.

Example: A flood kills most of a population at random. The survivors’ alleles now dominate. What is this? The survivors were chosen by chance, not by fitness. A sudden drop in numbers is a bottleneck. Answer: the bottleneck effect

Evidence & Mechanisms of Evolution in Alabama

In the Alabama Course of Study, this is unit 10 of 14 in 9th grade Science, after Reproduction and before Evolution & Selection.

Gradelings describes a child's practice on this unit as Beginning, Approaching, Meeting or Exceeding (Four practice steps). That reflects practice, not a report-card mark: the teacher decides the mark.

Source: Alabama State Department of Education (ALSDE)

Sample questions

A taste of this unit. In the app, questions change every time and get easier or harder to match your child.

  1. Question 1

    Gradualism says species change…

    • never
    • every year completely
    • only in sudden jumps
    • slowly and steadily over long periods

  2. Question 2

    Two populations separated by a new river can become different species because…

    • they no longer interbreed and change separately
    • rivers cause mutations
    • they share all genes
    • they mix more

  3. Question 3

    Stasis in the fossil record means a species…

    • changes every generation
    • moves continents
    • changes little over a long time
    • goes extinct at once

  4. Question 4

    A few birds start a new population on an island, carrying only some alleles. This is…

    • the founder effect
    • gene flow
    • codominance
    • stasis

  5. Question 5

    Many vertebrate embryos have similar tail and gill-like structures early on. This is…

    • genetic drift
    • biogeography
    • developmental homology
    • gene flow

  6. Question 6

    Scientists evaluate competing explanations for rates of change in the fossil record by…

    • taking a vote
    • comparing them with fossil evidence
    • choosing the oldest idea
    • ignoring gaps

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