Interpret ancestry evidence

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: Two lineages share underlying limb structures but use them differently. Explain why identical current function is unnecessary for homology.
• Assessment case 1: Two limbs share underlying bone organization but perform different tasks. What is supported? Which inference or prediction is best supported?
• Assessment case 2: Which scientific label fits the specifically described step or feature? Supplied case: Independent similar flight function in given model.
• Assessment case 3: Which scientific label fits the specifically described step or feature? Supplied case: Preserved ancestor-like structures in dated rock.
• Assessment case 4: Which scientific label fits the specifically described step or feature? Supplied case: Matching sequence patterns across species.
• Assessment case 5: Which scientific label fits the specifically described step or feature? Supplied case: DNA relationships support a branching model.
• Assessment case 6: A fossil sequence contains dated earlier and later forms with some shared structures. What can it support? Which inference or prediction is best supported?

Learn the idea

Common ancestry is supported by multiple evidence lines such as homologous structures, genetics and fossils. Similar appearance can also arise independently; one visible similarity is incomplete evidence.

Homology means similarity explained by shared ancestry. Analogy means similar function evolved independently in stated example. Fossil evidence means preserved evidence of past organisms. Genetic evidence means sequence comparisons supporting relationships.

For the supplied mechanism problem, Two lineages share underlying limb structures but use them differently. Explain why identical current function is unnecessary for homology. Homology concerns common ancestry of structures. Functions can diverge after ancestry. Independent similar function alone instead may be analogy, so structural and other evidence matter.

1. Read the supplied problem and mark the structures, processes or quantities named: Two lineages share underlying limb structures but use them differently. Explain why identical current function is unnecessary for homology.
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 comparison: underlying bone patterns support common ancestry, while similar color arose independently in the stated model. Expected: distinguish homology from an independently arising similarity; appearance alone is not a complete ancestry test.

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