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Extension

Evidence of Evolution 🔭︎

Explore how body structures across animals reveal the story of shared ancestry — and how life on Earth has changed over millions of years.

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Part I

Homologous Structures

Structures inherited from a common ancestor — same bones, different jobs.

Definition

In your own words, define homologous structures:

Part A — Function of Each Structure

Describe what each animal uses its forelimb structure for.

Animal Function of the structure
🧍Human
🐋Whale
🐱Cat
🦇Bat
🐊Crocodile
🐦Bird

Part C — Multiple Choice

What does it mean when different animals have bones that are built in a similar way, even if they use them for different things?
Part II

Analogous Structures

Structures that do the same job but evolved independently — similar function, different origin.

Definition

In your own words, define analogous structures:

Part B & C — Butterfly Wing vs. Bird Wing

Study the comparison below, then answer the questions.

🦋
Butterfly Wing
  • →Thin membrane stretched over hollow veins
  • →Covered in tiny overlapping scales
  • →No bones — entirely different structure from vertebrate limbs
  • →Insects evolved wings independently
🐦
Bird Wing
  • →Built from bones (humerus, radius, ulna, carpals)
  • →Covered in feathers attached to bone structure
  • →Same bone arrangement as human arm and bat wing
  • →Inherited from a common vertebrate ancestor
B. What is the job of the wings on both the butterfly and the bird?
C. How are the wings different?

Part D — Multiple Choice

Which of the following best describes analogous structures?
Part III

Vestigial Structures

Body parts that have faded in function over generations — evidence of what an ancestor once needed.

Definition

In your own words, define vestigial structures:

Cavefish vs. Minnow

These two fish are closely related — but they live in very different environments. Study the comparison, then answer the questions.

🐟
Minnow
  • →Lives in open streams and rivers with sunlight
  • →Has fully developed, functioning eyes
  • →Uses sight to find food and avoid predators
  • →Typical body shape for a freshwater fish
🫥
Cavefish
  • →Lives deep in underground caves — total darkness
  • →Eyes are greatly reduced or completely absent
  • →Same basic body structure and internal anatomy as minnow
  • →Eyes became vestigial over many generations in darkness
B. Why is eyesight not important for animals that live in dark caves?
C. What about the cavefish and the minnow suggests they share a common ancestor?
D. What sense do you think is most important for the cavefish?
Explain your answer:
🔬 Synthesis

Putting It All Together

Use everything from Parts I–III to tackle one final challenge question.

⚡ Challenge Question

The Common Ancestor Claim

"A student says: 'Bat wings and bird wings prove that bats and birds share a common ancestor.' Is this student correct? Use what you know about homologous vs. analogous structures to explain your answer."

Double-check your answers before submitting. You can only submit once.

🔬 Learning Science Focus 🔀 Interleaved Comparison 💬 Elaboration ✅ Retrieval Practice
📋 MA STE Standards · Grade 7–8 MS-LS4-2 MS-LS4-1