Lecture Notes: Homologous and Analogous Structures

Overview

• Homologous Structures: Anatomical structures that are similar structurally but have different functions.
• Analogous Structures: Structures that are anatomically different but have similar functions.

Homologous Structures

• Examples:
  • Arm of a human
  • Leg of a cat
  • Leg of a horse
  • Wing of a bat
  • Flipper of a dolphin
• Characteristics:
  • Despite different functions, these structures display similar anatomy.
  • Common anatomical features include:
    • Humerus
    • Two forearm bones: Radius (green) and Ulna (yellow)
    • Metacarpals and Phalanges
  • Dolphins, like humans, have five phalanges.
• Functions:
  • Horse: Walking and running
  • Bat: Flying
  • Dolphin: Swimming
• Evolutionary Perspective:
  • Homologous structures suggest a common ancestor among species (human, cat, horse, bat, dolphin).

Analogous Structures

• Examples:
  • Wing of an insect vs. Wing of a bird
  • Leg of a horse vs. Leg of a grasshopper
• Characteristics:
  • Structurally different:
    • Insect wings vs. Bird wings
    • Horse leg (joints, tendons, ligaments) vs. Grasshopper leg (segmented, exoskeleton)
• Functions:
  • Both wings are used for flight.
  • Both legs serve for locomotion.
• Evolutionary Perspective:
  • Not associated with common ancestors.
  • Associated with convergent evolution.

Evolutionary Concepts

• Divergent Evolution: Associated with homologous structures.
• Convergent Evolution: Associated with analogous structures.