Dr. Alemseged is a paleoanthropologist, studying human evolution. In 2000, he discovered an almost-complete Australopithecus afarensis skeleton fossil. This fossil came from a young female (~3 years old) from the same species as Lucy, but had lived ~150,000 years earlier. He named her Selam.

Dr. Alemseged is originally from Ethiopia and received his undergraduate degree from Addis Ababa University. He received an M.S. from the University of Montpellier II and a Ph.D. from Paris-Sorbonne University, both in France. He completed postdoctoral training at the Institute of Human Origins at Arizona State University. Prior to joining the faculty at the University of Chicago in 2016, he was a Senior Scientist at the Max Planck Institute for Evolutionary Anthropology in Germany and the Irvine Chair and Senior Curator of Anthropology at the California Academy of Sciences.

While we can learn a lot about human evolution by comparing ourselves to related primates (chimpanzees, gorillas, etc.), we are somewhat limited by the fact that we don’t know when those differences arose. For instance, differences between our spines and those of apes are thought to have contributed to the evolution of our ability to walk upright. But we don’t know exactly when those changes happened or how. Our spines are made up of three types of vertebrae: cervical (neck), thoracic (ribcage), and lumbar (lower back) – have the boundaries between those segments changed or have we gained and lost some vertebrae within each segment?

The fossil of Selam can help answer this question, as Dr. Alemseged and colleagues recently reported. This fossil contains the only full set of thoracic vertebrae from an early hominid. Based on that, Dr. Alemseged was able to conclude that she had 12 thoracic vertebrae like modern humans, and not 13 like most modern apes.

In addition, the researchers looked at the transition from the thoracic region to the lumbar region. In most people, there is a gradual transition, where the lowest two or three thoracic vertebrae slowly shift to being more lumbar-like. In contrast, in previously-discovered early hominid fossils, there is an abrupt transition: the top of one vertebra looks thoracic and the bottom looks lumbar. Strangely, it is usually the second-lowest thoracic vertebra and not the lowest… This pattern was also seen in Selam.

These two conclusions suggest that changes in spinal composition resulted from changes in the boundaries between segments and not from gain/losses within individual segments. Additionally, they suggest that these early hominids likely had much less rotation in their spines than we do, which would have made long-distance walking and running difficult. This provides new information for trying to understand when and in what order the necessary changes occurred in our spines that allowed us to be bipedal.