ABSTRACT
Alignment of the body in an upright position is itself the key to human bipedalism and has been associated in evolution with decoupling of head and trunk movements. This has allowed us to develop the capability
for endurance running. As the hindlimbs progressively assumed the role of locomotion, the vertebral column adapted from a horizontal compressed structure to a vertical weight-bearing rod and axial rotations and counter-rotations of the trunk developed to permit a wide range of activities unique to man to evolve. The relationship between the spine and the pelvic girdle distally and the skull proximally also changed, and changes occurred in the shape of the pelvis and sacrum. The centre of gravity also evolved, shifting backwards towards the hindlimbs as their length and musculature increased. At the same time, to reduce energy expenditure in countering needless body rotation about the centre of gravity, forces for forward propulsion passed through the centre of gravity. Early changes in body form also allowed the adoption of sitting positions, allowing the forelimb to be freed for manipulative functions. Further changes in the angulations of the lumbar vertebral column in females also enabled them to carry babies, an evolutionary trend that gave humans an advantage over potential predators (Whitcombe et al. 2007). Additionally, associated increases in fl exibility of the vertebral column were accompanied by changes in size of the vertebrae in the lumbar
region, which became more massive in order to cope with increased compression forces resulting from the upright stance. Further changes in the role of the sternum and abdominal muscles occurred which allowed less truncal stiffness, resulting in the wider shallow chest and reduced angulation of the ribs of humans.
