Homologous structures are physical features shared by two or more species because they were inherited from a common ancestor. The structures may have different functions in the present-day species, but their underlying anatomy or genetic sequence reveals their shared origin.

When Charles Darwin set sail on the HMS Beagle , he carried a simple question: Why do different creatures sometimes look alike, and why do close relatives sometimes look radically different? The answers lie in two deceptively simple concepts: and analogy .

5. Categorize the following pairs as Homologous or Analogous: Shark fin and Dolphin fin: Analogous (Fish vs. Mammal). Cactus spine and Rose thorn: Analogous (Different plant tissues). Cat leg and Dog leg: Homologous (Shared mammalian ancestor). Dragonfly wing and Pterodactyl wing: Analogous (Insect vs. Reptile). Critical Thinking: The "Ancestry" Test If you are stuck on a question, ask: