Unit 08 · Comparative Anatomy & the Dissection Defense
This synthesis unit compares the specimens as branches of animal diversity, not steps toward a human body. You compare organ systems, distinguish shared function from evidence of shared ancestry, and explain homologous structures using the anatomy you can actually observe. The capstone remains a live dissection defense: locate a structure, name it, explain its function, and defend the evidence under questioning. Use labeled skeletal references for bones not exposed on the specimen; distinguish a reference-based inference from a direct observation.
| Criterion | Developing | Proficient | Mastery |
|---|---|---|---|
| Comparing structures across specimens | Cannot locate the same organ system in two specimens. | Finds both systems but assumes a shared job proves homology. | Compares an organ system in two specimens and distinguishes shared function from evidence of shared ancestry. |
| Homology vs. analogy | Treats any two structures that do the same job as the same structure. | Uses the words homology and analogy but applies them to the wrong examples. | Distinguishes homologous structures (shared plan, shared descent) from analogous ones (same function, separate origin) on the actual specimens. |
| The dissection defense | Cannot locate or name the requested structure on the specimen when asked aloud. | Finds and names the structure but cannot explain its function or answer a follow-up question. | Locates, identifies, and explains a structure’s function on the specimen out loud, and holds up under an instructor’s questioning. |
| The common-descent argument | Cannot relate anatomical evidence to common descent. | Names homology but treats living species as successive ancestors. | Explains the shared tetrapod forelimb pattern and places the specimens on a branching tree, stating the limits of the comparison. |
| Synthesis & careful communication | Reports expected rather than observed anatomy; handles specimens carelessly. | Names most structures but blurs observation and inference. | Uses accurate terms, separates observation from inference, and handles specimens respectfully. |
| Integration (cross-domain) | Makes no supported connection between the source and the science. | Uses the source but needs help connecting evidence, writing, or limitations to the science. | Independently connects History, Reading, and Writing using a cited source, appropriate evidence, a limitation, and a scientific explanation. |
Integration is reported separately and cannot lower the science grade or block a science demonstration pass. Science and practical criteria determine that pass. Use the integration guide's evidence checklist for the separately reported criterion.
“The frog forelimb, pig forelimb, and human arm share an inherited bone pattern, with changes such as fused bones and different digit counts. The perch is a ray-finned fish: its fin does not show that full tetrapod limb pattern. These living animals are branches with shared ancestors, not steps from worm to human.”
“Both structures move the animal, so they must have the same origin. I cannot point to the parts that support that claim.”
You demonstrate this unit by defending a real specimen and a valid cross-specimen comparison aloud. Explain which features support homology, which similarities concern function alone, and what the available specimens cannot show. Use a labeled reference when a structure is not exposed, without claiming to have observed it directly. Mastery is demonstrated, not awarded.
A 5-page clipboard packet — unit overview, key terms, the mastery rubric, anchor examples, and a score sheet you can print and grade against.