Chapter 8

Primate and Hominin Origins

Walking on two feet?• How does that work?

Bipedalism!• To walk habitually on two feet, there had to

be substantial changes to the pelvis, knees, and feet.

• The Pelvis is comparatively much shorter and broader than an Ape’s and extends around to the side, stabilizing the line of weight transmission from lower back to hip joint

• Example…

Human Os Coxae

• The human os coxae is composed of three bones (right side shown).

Ossa Coxae (“hip bones”)

• (a) Homo sapiens.• (b) Early hominin from

South Africa. • (c) Great ape.• Note the length and

breadth of the iliac blade (boxed) and the line of weight transmission.

More Ossa Coxae

Bipedalism!• To walk habitually on two feet, there had to

be substantial changes to the pelvis, legs/knees, and feet.

• The Legs and Knees …

Land on heal

· Push off toes

· Longer limbs to maximize movement

· Full extension of Knee

Longer legs, full knee extension

Femur - The femur is angled inward, keeping legs under the body

Bipedalism!• To walk habitually on two feet, there had to

be substantial changes to the pelvis, legs/knees, and feet.

• The Feet…

Foot as stable suport

Models on WHY?• Why we became bipedal (6 hypotheses)

Efficient bipedalism as the primary form of locomotion is seen only in hominins.