Speciation and the Rate of Evolution · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

When one species becomes two

Science · Genetics & Evolution · ages 15-16
Name ______________________   Date ____________

  1. In the river-isolation route to speciation, which event separates the original gene pool?

    • A barrier stops gene flow
    • They learn new songs
    • Fossils form in the rocks

  2. For sexually reproducing organisms, which feature groups populations into one biological species?

    • They look identical
    • They normally breed fertile young
    • They live in one place

  3. Two similar bird populations are reproductively isolated: they cannot interbreed and produce fertile young. Under the biological species concept, what does this support?

    • They share one gene pool
    • They migrate together
    • Separate species

  4. A river splits squirrels, then their breeding seasons stop overlapping. Which barrier is each?

    • River is reproductive, season shift is geographic
    • Both are geographic barriers
    • River is geographic, season shift is reproductive

  5. For the river-isolation example, order these stages: reunion fails, barrier appears, differences pile up.

    • Barrier appears, differences pile up, reunion fails
    • Reunion fails, barrier appears, differences pile up
    • Differences pile up, reunion fails, barrier appears

  6. Why can island finches evolve rapidly with new food sources, while some traits stay similar under stable pressures?

    • Islands freeze all change
    • Different selection pressures
    • Sharks never mutate

  7. After a mass extinction, fossils record many new forms over the following millions of years. What can explain this diversification?

    • Fossils form faster after crashes
    • Mutations stop during crashes
    • Survivors adapt to open niches

  8. A student finds two fossils that look alike and declares one species. What is the error?

    • Looks alone cannot establish a species
    • Only living animals form species
    • Fossils never carry evidence
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Answer key

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

When one species becomes two W1-mt_OdcdfeRyo1-s1

  1. A barrier stops gene flow · Isolation lets each side pile up its own differences.
  2. They normally breed fertile young · Under the biological species concept, populations that normally interbreed and produce fertile offspring are grouped together.
  3. Separate species · The populations cannot exchange genes through successful breeding, supporting separate biological species.
  4. River is geographic, season shift is reproductive · Rock and water block meeting, while seasons block mating itself.
  5. Barrier appears, differences pile up, reunion fails · Isolation comes first, change accumulates, then merging fails.
  6. Different selection pressures · New food sources can favour different beaks. Stable pressures may keep favouring similar traits.
  7. Survivors adapt to open niches · Available ecological roles can let surviving lineages diversify. Recovery still takes many generations.
  8. Looks alone cannot establish a species · The fossils cannot be bred to test compatibility, and usually lack DNA. More anatomical and fossil evidence is needed.
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