Question

the diagram shows the bone structure of the front legs of two animals: a frog (amphibian) and an alligator (reptile). shading is used to identify similar bones. how does a comparison of the bone structures of the two animals provide evidence of an evolutionary relationship? a. the analogous structures are evidence that one animal evolved from the other. b. the homologous structures are evidence of descent with modification from a common ancestor. c. the homologous structures are evidence that one animal evolved from the other. d. the analogous structures are evidence that the two animals do not share a recent common ancestor.

Explanation:

1. First, recall the definitions of homologous and analogous structures:

• Homologous structures are structures that are similar in form (anatomically) but may have different functions, and they are evidence of descent from a common ancestor (with modification, as the structures adapt to different uses).
• Analogous structures are structures that have similar functions but different evolutionary origins (not from a common ancestor).

1. Analyze Option A: Analogous structures do not indicate one evolved from the other (they have different origins), so A is incorrect.
2. Analyze Option B: The bone structures of the frog (amphibian) and alligator (reptile) are homologous (similar in anatomical layout, suggesting a common ancestor). Homologous structures are evidence of descent with modification from a common ancestor, so this matches the concept.
3. Analyze Option C: Homologous structures actually suggest a common ancestor, so the idea that one evolved from the other in a direct way (rather than from a common ancestor) is incorrect. Homologous structures show divergence from a common ancestor, not a direct evolutionary path from one to the other.
4. Analyze Option D: Analogous structures would suggest no recent common ancestor, but these are homologous structures, so D is incorrect.

Answer:

B. The homologous structures are evidence of descent with modification from a common ancestor.