There are six major structural reorganizations that have taken place throughout the body during hominid evolution to allow for efficient bipedal
locomotion. In more straightforward terms, humans have gone through some changes to walk on two legs without wasting unnescessay energy. Here they are:
- The foramen magnum of the great apes is located on the back of the head to allow for robust neck muscles and to place the head in the proper position for walking on all fours. As hominids evolved, the foramen magnum gradually moved to its current position underneath the skull. Therefore the head is held upright and is properly balanced over the spine, and bipedal locomotion is no longer awkward.
- Spine Curvature is crucial for efficient upright walking. The spine has two major curves, the thoracic (where the back curves away from the chest) and the lumbar (where the spine curves towards the stomach). These curves keep the trunk of the body, and the weight of it, centered above the pelvis.
- The shape of the pelvis has changed dramatically. In the great ape, the ossa coxae, more specifically the iliac blades, are much more elongated than modern humans. For humans, the shorter and broader ossa coxae stabilize the weight transmission while walking. Over thousands of years, the pelvis changed into a more basin-type shape (in Latin, pelvis = “basin”). It is now capable of supporting the internal organs, although giving birth is definitely harder due to the shape.
- Limb length has obviously changed during hominid evolution. In modern humans, the thigh makes up 20% of the body’s length, while in the great apes, it is only 11%. Arm length has decreased in proportion to body size as well – human upper arms are 9.4% of their height, which great apes’ are 15.5%.
- The knee and femur have changed slightly – in humans, the knee anatomy has evolved so that we can fully extend our legs while walking. Our femurs are also angled slightly inward to keep the knees directly under the body.
- The foot has undergone some major changes throughout hominid evolution. In humans, the big toe is enlarged and brought in line with the rest of the toes, and a distinctive longitudinal arch has formed to absorb shock and add propulsive spring while walking.
There have been several other changes, both minute and dramatic, in other parts of the body during hominid evolution. Cranium
forms have evolved, as well as overall brain
size. For more information, take a look at any text entitled Introduction to Physical (or Biological) Anthropology
. There’s a lot of interesting and controversial stuff to learn.