Derived Adaptations: Bipedalism

Bipedalism: A Defining Trait of Hominins

Introduction to Bipedalism

  • Obligate bipedalism, the habitual upright walking of modern humans, distinguishes us from extant great apes.
  • It is considered a defining attribute of the hominin lineage.
  • Unlike other bipedal animals (e.g., kangaroos), humans lack a tail for balance.

The Origin of Bipedalism: Two Main Ideas

  1. Arboreal Last Common Ancestor (LCA) Theory:

    • Early hominins lived in trees but gradually transitioned to ground-dwelling.
    • This suggests we evolved from an arboreal LCA.

  2. Terrestrial Quadrupedal Knuckle-Walking LCA Theory:

    • The LCA was a terrestrial quadrupedal knuckle-walking species, similar to chimpanzees.

Support for the Arboreal LCA Theory

  • Most research favors the arboreal LCA theory based on skeletal morphology.
  • Early hominin genera show adaptations for climbing, not knuckle-walking.
  • This implies humans and chimpanzees are