Here's why:
* Analogous structures have similar functions but different underlying structures and evolutionary origins.
* Homologous structures have similar underlying structures due to a shared common ancestor, even if their functions differ.
Shark fins and dolphin fins are similar in function: Both are used for swimming, maneuvering, and balance.
But, they differ in structure and origin:
* Shark fins are supported by cartilage, which is a type of flexible connective tissue.
* Dolphin fins are supported by bones, which are harder and more rigid.
Sharks and dolphins evolved from very different ancestors, millions of years apart. The similarity in their fins is a result of convergent evolution, where unrelated species evolve similar traits due to adapting to similar environments and lifestyles.