When Did Humans Start to Walk? 3.3 Million-Year-Old, Fossil Tells All

The vertebrae of the Selam skeleton. (Image:    University of Chicago Medical Center)
The vertebrae of the Selam skeleton. (Image: University of Chicago Medical Center)

A new study has found the human spinal structure that enables efficient walking motions was established millions of years earlier than previously thought. This 3.3 million-year-old fossil skeleton is the most complete spinal column of any early human relative; it includes the vertebrae, neck, and rib cage.

The fossil is a near complete skeleton of a 2½-year-old child known as “Selam,” which means “peace” in the Ethiopian Amharic language. The skeleton was found in Dikika, Ethiopia, in 2000 by Zeresenay (Zeray) Alemseged, professor of organismal biology and anatomy at the University of Chicago, and senior author of the new study.

Zeray Alemseged at the site in Dikika, Ethiopia, where he discovered Selam. (Image: via Zeray Alemseged)

Zeray Alemseged at the site in Dikika, Ethiopia, where he discovered Selam. (Image: via Zeray Alemseged)

“Selam” is an early human relative from the species Australopithecus afarensis — the same species as the famous Lucy skeleton. After the discovery of “Selam,” Alemseged began slowly chipping away at the sandstone that surrounded the skeleton. Alemseged said in a statement:

Now, with the sandstone removed, they have been able to use advanced imaging tools to further analyze its structure. Co-author of the study Fred Spoor, a professor of evolutionary anatomy in the Department of Biosciences at the University College London, said:

Full skeleton of Selam, a 3.3 million-year-old Australopithecus afarensis fossil discovered by Zeray Alemseged in 2000. (Image: via University of Chicago Medical Center)

Full skeleton of Selam, a 3.3-million-year-old Australopithecus afarensis fossil discovered by Zeray Alemseged in 2000. (Image: via University of Chicago Medical Center)

There are many features of the human spinal column and the rib cage that are shared among primates; however, the human spine also reveals our distinctive mode of walking upright. For example, the human has fewer rib-bearing vertebrae (bones of the back) than that of our closest primate relatives.

Humans also have more vertebrae in the lower back (allows us to walk effectively). It has been unknown until now when and how this pattern evolved. This has been because complete sets of vertebrae are very rarely preserved in the fossil record. Alemseged explained:

Carol Ward, a Curator’s Distinguished Professor of Pathology and Anatomical Sciences in the University of Missouri School of Medicine and lead author on the study, said in a statement:



The researchers found that “Selam” had the unique thoracic-to-lumbar joint transition found in other human relatives. However, it was also the first to show that, like modern humans, our earliest ancestors had only 12 thoracic vertebrae and 12 pairs of ribs. Thierra Nalley, an assistant professor of anatomy at Western University of Health Sciences in Pomona, California, and an author on the paper, said:

The configuration marks a shift toward the type of spinal column that allows humans to be the efficient walkers and runners we are today. Alemseged went on to say:

Skull of Selam, a 3.3 million-year-old Australopithecus afarensis fossil discovered by Zeray Alemseged in 2000. (Image: via University of Chicago Medical Center)

Skull of Selam, a 3.3-million-year-old Australopithecus afarensis fossil discovered by Zeray Alemseged in 2000. (Image: via University of Chicago Medical Center)

Either way you look at this, it clearly shows how much we don’t know about ourselves.

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