Homologous Structures Are Evidence For Evolution
Definition
Homologous structures
Homologous structures are anatomical features that share a similar structure and position across different species but serve different functions.
- Homologous structures have a similar structural layout, despite differences in function.
- They serve as evidence of inheritance from a common ancestor.
- They illustrate the concept of "unity of type" (shared design due to common ancestry, as coined by Charles Darwin).
A human hand (grasping), a bird wing (flying), and a whale flipper (swimming) all follow the same basic bone arrangement but are specialized for different activities.
The Pentadactyl Limb: A Classic Example
- The pentadactyl limb is the foundational structure seen in all tetrapods (four-limbed vertebrates).
- It consists of:
- Proximal Bone (single): Humerus in the forelimb, femur in the hindlimb.
- Distal Bones (paired): Radius and ulna in the forelimb, tibia and fibula in the hindlimb.
- Wrist/Ankle Bones: Carpals in the forelimb, tarsals in the hindlimb.
- Digits (fingers/toes): Metacarpals and phalanges in the forelimb, metatarsals and phalanges in the hindlimb.
