Sexual dimorphism in the vertebral wedging of the human lumbar vertebrae and its importance as a comparative framework for understanding the wedging pattern of Neanderthals

Abstract

Lumbar lordosis is a key element of the upright posture, being interpreted as a consequence of bipedal locomotion. There is consensus that the generic modern human pattern of metameric vertebral body wedging is sexually dimorphic in modern humans. However, recently published studies have compared this pattern with other hominins, such as Neanderthals. These tried to establish whether the (male) Neanderthal lumbar vertebrae express a pattern that falls within or outside the range of modern human males. In the present study, data collected by 3D landmarks of the lumbar vertebrae of modern humans from different geographic regions and Neanderthals (Ntotal = 505 individual vertebrae) are used to clarify this problem, observing a similarity of the generic human pattern but with some interspecific differences in the pattern in the upper and lower lumbar vertebrae. Thus, the vertebral bodies L1-L3 of Neanderthals are more ventrally-wedged than in male modern humans, whilst the L4-L5 vertebral bodies of Neanderthal show a more progressive increase of dorsal wedging than in modern human males. The obtained results support modularity of the lumbar spine with different patterns in its upper and lower parts, and add that human geographic variability must be taken into account when carrying out comparisons of Neanderthals and modern humans. Our findings make clear the need to investigate this matter in more detail including complementary methods. Finally, key issues concerning the choice of measurement are discussed and recommendations made about how much inference can be made about complex systems such as the lumbar spine based on single linear measurements.