Separate variation and selection

Supplied materials

• All measurements and observations below are supplied classroom examples. They are not data from actual learners or a claim about a particular real site.
• Paper or a browser document for a labeled drawing, table or explanation.
• Worked problem inputs: A dry habitat changes; an inherited variant already present leaves more offspring. Explain the sequence without intent.
• Assessment case 1: A heritable beak-size variant exists before drought and leaves more offspring during drought. What sequence fits? Which inference or prediction is best supported?
• Assessment case 2: Which scientific label fits the specifically described step or feature? Supplied case: Offspring inherit relevant information.
• Assessment case 3: Which scientific label fits the specifically described step or feature? Supplied case: Some inherited variants leave more offspring.
• Assessment case 4: Which scientific label fits the specifically described step or feature? Supplied case: Variant becomes more common after generations.
• Assessment case 5: Which scientific label fits the specifically described step or feature? Supplied case: Variation exists before a habitat change.
• Assessment case 6: A variant’s frequency rises over generations, but heredity and offspring differences are unmeasured. What is warranted? Which inference or prediction is best supported?

Learn the idea

Individuals vary before selection occurs. If inherited differences affect reproductive success, their frequencies can change over generations. Organisms do not intentionally evolve a needed trait.

Variation means differences among individuals. Inheritance means biological information transmitted to offspring. Selection means differing reproductive success tied to traits. Population change means trait frequencies differ over generations.

For the supplied mechanism problem, A dry habitat changes; an inherited variant already present leaves more offspring. Explain the sequence without intent. Variation precedes the changed selective conditions. Differential reproduction can make the inherited variant more frequent over generations. Individuals do not deliberately create the needed variant.

1. Read the supplied problem and mark the structures, processes or quantities named: A dry habitat changes; an inherited variant already present leaves more offspring. Explain the sequence without intent.
2. Draw the relevant boundary, pathway or comparison and label it using the scientific ideas above.
3. Write a causal explanation or calculation, showing how each observation supports the result.
4. Compare your reasoning with the worked solution; name a condition that would change or limit the inference.

Check your reasoning

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Take it further

New case: inherited variant X leaves more offspring after a food change; a learned trick improves one individual but is not supplied as inherited. Expected: distinguish population selection on X from individual learning; do not claim organisms choose new inherited variants.

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