Bipedalism

Question 1

Why did hominins became bipedal? What are some advantages?

Answer 1

Hominins became bipedal due to the change in environment that 24/25 Ma BP happened in Africa: from a tropical climate, it became a savannah.

Advantages:

• Food more easily carried
• Allows living far from home base
• Better overview of the surroundings and could easily spot danger
• Energy
• Better regulation of body temperature.

Question 2

What anatomical changes are associated with bipedalism?

Answer 2

1. Foramen magnum in basicranium
2. Lateral orientation of shoulder joints (allow swinging arms, which helps with equilibrium)
3. Barrel-shaped chest
4. S-shaped spine (upper curve is called kyphosis, lower curve is called lordosis), which absorb shock
5. Change in pelvic structure, to allow the difficult delivery of babies:
   
   • shortened and wider
   • illium shorter and tilted backwards
   • isonium shorter bend
   • pubis directed frontally
   • larger distance between left and right acetabulum
6. Changes in muscle structure:
   
   • musculus gluteus maximus became an extensor
   • musculus gluteus medius remained an abductor
   • musculus sartorius involved in forward extension
7. Changes in the inclination of the knee joint, in the valgus angle and in the obturator groove
8. Calcaneus became more elongated, to allow better leverage, more pronated and the hallux abduction decreased