Abstract
BackgroundRecently we proposed an evolutionary explanation for a spinal pathology that afflicts many people, intervertebral disc herniation (Plomp et al. [2015] BMC Evolutionary Biology 15, 68). Using 2D data, we found that the bodies and pedicles of lower vertebrae of pathological humans were more similar in shape to those of chimpanzees than were those of healthy humans. Based on this, we hypothesized that some individuals are more prone to intervertebral disc herniation because their vertebrae exhibit ancestral traits and therefore are less well adapted for the stresses associated with bipedalism. Here, we report a study in which we tested this “Ancestral Shape Hypothesis” with 3D data from the last two thoracic and first lumbar vertebrae of pathological Homo sapiens, healthy H. sapiens, Pan troglodytes, and several extinct hominins.ResultsWe found that the pathological and healthy H. sapiens vertebrae differed significantly in shape, and that the pathological H. sapiens vertebrae were closer in shape to the P. troglodytes vertebrae than were the healthy H. sapiens vertebrae. Additionally, we found that the pathological human vertebrae were generally more similar in shape to the vertebrae of the extinct hominins than were the healthy H. sapiens vertebrae. These results are consistent with the predictions of the Ancestral Shape Hypothesis. Several vertebral traits were associated with disc herniation, including a vertebral body that is both more circular and more ventrally wedged, relatively short pedicles and laminae, relatively long, more cranio-laterally projecting transverse processes, and relatively long, cranially-oriented spinous processes. We found that there are biomechanical and comparative anatomical reasons for suspecting that all of these traits are capable of predisposing individuals to intervertebral disc herniation.ConclusionsThe results of the present study add weight to the hypothesis that intervertebral disc herniation in H. sapiens is connected with vertebral shape. Specifically, they suggest that individuals whose vertebrae are towards the ancestral end of the range of shape variation within H. sapiens have a greater propensity to develop the condition than other individuals. More generally, the study shows that evolutionary thinking has the potential to shed new light on human skeletal pathologies.
Highlights
We proposed an evolutionary explanation for a spinal pathology that afflicts many people, intervertebral disc herniation (Plomp et al [2015] BMC Evolutionary Biology 15, 68)
Because Homo and Pan share an exclusive common ancestor and there is general agreement that that ancestor was a quadruped (e.g. [31,32,33]), we proposed that our finding indicated that people who experience intervertebral disc herniation do so because their vertebrae fall at the ancestral end of the range of variation in H. sapiens and, are less well adapted for the stresses associated with bipedalism
Our study focused on the thoracic and lumbar vertebrae of three extant taxa—H. sapiens with Schmorl’s nodes, healthy H. sapiens, and P. troglodytes—and five extinct hominin taxa—Australopithecus africanus, Australopithecus sediba, Paranthropus robustus, Homo naledi, and Homo neanderthalensis
Summary
We proposed an evolutionary explanation for a spinal pathology that afflicts many people, intervertebral disc herniation (Plomp et al [2015] BMC Evolutionary Biology 15, 68). Using 2D data, we found that the bodies and pedicles of lower vertebrae of pathological humans were more similar in shape to those of chimpanzees than were those of healthy humans. Up to two-thirds of people experience back pain at some point in their life [1, 2], making it one of the most common medical problems. It is one of the most serious medical conditions. Given the individual and societal costs of back pain, there is a pressing need for further research on its causes
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