Human evolution: upright posture requires spinal changes (Introduction)

by David Turell , Tuesday, December 07, 2021, 20:04 (869 days ago) @ David Turell

In the lumbar area:

https://elifesciences.org/articles/70447

"Adaptations of the lower back to bipedalism are frequently discussed but infrequently demonstrated in early fossil hominins. Newly discovered lumbar vertebrae contribute to a near-complete lower back of Malapa Hominin 2 (MH2), offering additional insights into posture and locomotion in Australopithecus sediba. We show that MH2 possessed a lower back consistent with lumbar lordosis and other adaptations to bipedalism, including an increase in the width of intervertebral articular facets from the upper to lower lumbar column (‘pyramidal configuration’). These results contrast with some recent work on lordosis in fossil hominins, where MH2 was argued to demonstrate no appreciable lordosis (‘hypolordosis’) similar to Neandertals. Our three-dimensional geometric morphometric (3D GM) analyses show that MH2’s nearly complete middle lumbar vertebra is human-like in overall shape but its vertebral body is somewhat intermediate in shape between modern humans and great apes. Additionally, it bears long, cranially and ventrally oriented costal (transverse) processes, implying powerful trunk musculature. We interpret this combination of features to indicate that A. sediba used its lower back in both bipedal and arboreal positional behaviors, as previously suggested based on multiple lines of evidence from other parts of the skeleton and reconstructed paleobiology of A. sediba."

Comment: upright posture requires pelvic changes and a development of lumbar lordosis, which apes do not have. Why these changes appeared presents a chicken and egg question. Did continuous attempts at bipedal locomotion produce the change? Not likely with a dependence upon chance mutations. On the other hand if provided with the proper spinal anatomy upright, posture becomes easy to manage. Design is obvious.