Evolutionary development of the spine. The background of modern back problems?

Back problems are a very common health concern in humans and most people are going to suffer from some sort of back pain at some point in their lives. It has been suspected that the roots of the back problems might partly lie with bipedal locomotion and upright posture. The observations that back issues appear to be less common in other hominoids would seem to support this. For this reason, the dissertation investigated how the vertebrae have evolved during the evolution and how posture and locomotion may have affected the vertebrae. This can help us to understand how the vertebrae have evolved to accommodate the new posture and locomotion. However, in addition to evolutionary changes in locomotion and posture, the human lifestyle has also gone through dramatic changes in recent history, and we now live the most sedentary lifestyle in our history. This has brought a completely new set of requirements for the back. Hence, it is also important to understand the changes that have taken place in a shorter time span and what impact these changes could have on our spinal health.

To study the evolutionary changes, differences in the shape of the vertebral bodies were investigated between modern humans, African apes and fossil hominoids. Also, the bone density of multiple vertebrae of the African apes was studied and compared to results from humans to see how they differ. The short time span changes were studied by observing the differences in the size and shape of the vertebral body between Finnish archaeological individuals (from the 17th to 19th century) and contemporary humans from Northern Finland Birth Cohorts (a longitudinal research program). In addition, age-related bone density changes were studied in 20th century American population. The dissertation concentrated on the lower back as it is most vulnerable to pain.

The results indicated that there have not been large changes in vertebral shape during the evolution. Vertebral body shape seemed to be similar between humans and gorillas, which could indicate that the loading of the vertebrae might influence the shape more than the locomotion style. This is also supported by the observation that chimpanzees clearly differed from humans and gorillas. Chimpanzees also had relatively round vertebral bodies compared to the fossil hominoids. Instead, the pattern of bone density fluctuation between adjacent vertebrae in the whole spine seems to be relatively similar between humans and chimpanzees. Whereas differences were found between the ape species which might indicate less influence of locomotion on this feature.

The short time span changes indicated that contemporary humans have more round shaped vertebral bodies than in the past, which could influence both vertebral strength and intervertebral disc health. The age-related bone density loss was observed to have been different in the 20th century American population. Especially the females in the past experienced less age-related vertebral bone loss compared to contemporary females. In both short time span changes, it was suspected that the large decline in the physical activity levels and sedentary lifestyle of contemporary humans could have influenced the vertebral bodies. Bones respond to physical strain and the decreased physical strain could lead to changes that are not necessarily positive in the light of spinal health.