Analysis of a 3.3 million-year-old fossil skeleton has revealed the most complete spinal column – including the vertebrae, neck, and rib cage – of an early human. The results of scientists at the University of Chicago (USA) indicate that the human vertebral structure that allowed us to run was established millions of years earlier than previously thought.
The fossil, known as “Selam” (Peace), forms an almost complete skeleton of a 2 and a half year old boy discovered in 2000 in Dikika (Ethiopia) by Zeresenay (Zeray) Alemseged, the study leader. “Selam” belongs to the same species as Lucy , Australopithecus afarensis .
“Continuous and careful research on Selam shows that the general structure of the human spine emerged more than 3.3 million years ago, shedding light on one of the hallmarks of human evolution. This kind of preservation is unprecedented, particularly in a young individual whose vertebrae are not yet fully fused, “explains Alemseged.
The human spine reflects our distinctive way of walking upright on our feet, hence humans have fewer vertebrae in the back than our closest primate relatives, but we have more vertebrae in the lower back, allowing us walk freely and run. When and how this pattern evolved was unknown until now because complete sets of vertebrae are rarely preserved in the fossil record.
“For many years we have known of fragmentary remains of early fossil species suggesting that the shift from rib or thoracic vertebrae to lumbar or lower back vertebrae was located higher in the spine than in living humans. Selam it has provided us with the first insight into how the vertebrae of our ancestors ‘ ancestors were organized, “explains Carol Ward, co-author of the work.
The researchers used high-resolution imaging technology to visualize ‘Selam’s’ bones. The scans indicated that Selam had the characteristic thoracic-lumbar transition of other human fossil relatives, but he is the first to show that, like modern humans, our earliest ancestors had only 12 thoracic vertebrae and 12 pairs of ribs. Much less than in most apes.
“This unusual early human configuration may be a key in developing more accurate scenarios about the evolution of bipedalism and the modern shape of the human body,” says Thierra Nalley of the Western University of Health Sciences in Pomona, California.
Selam’s configuration thus marks a transition towards the type of spinal column that allowed humans to be so efficient in both walking and running.
“This structure and its modification through time is one of the key events in the history of human evolution.”
The study has been published in the journal Proceedings of the National Academy of Sciences (PNAS).
Image Credit: Zeray Alemseged, University of Chicago
