Anatomy professor published in Scientific Reports

Dr. David Green, associate professor of anatomy, co-authored a paper published today in Scientific Reports with Daniel Garcia-Martinez and Jose Maria Bermudez de Castro, paleoanthropologists from the National Center for Research on Human Evolution (CENIEH) in Burgos, Spain .

Dr. David Green

Their published findings suggest that Homo antecessor shoulder development was nearly identical to that of Homo sapiens. The authors concluded that H. antecessor shoulders were already very similar to modern humans, even during the Lower Pleistocene (~850,000) years ago.

“This is my first foray into a study of “archaic” humans, ancient hominins that are more humanlike than apes, but clearly not what we call “anatomically” modern,” Green explained.

“Studying comparative anatomy helps us understand the form/function relationship between the shape of our bones and how that enables us to move the way we do. Comparative anatomy is integral to studying fossils for helping contextualize the way that this form/ function relationship has changed over time. We use these associations to interpret the behavioral attributes of extinct forms (i.e., their “paleo”biology),” Green explained.

“Much of my previous work has been with older, more primitive groups like Australopithecus, Homo erectus, and Paranthropus. Our findings are consistent with hypotheses that at least from the neck down, more recent groups like H. antecessor were nearly identical to modern humans, perhaps with some regional, environmentally-influenced adaptations.”

Dr. Green did his dissertation on human and ape scapular development at The George Washington University. He met Dr. Garcia-Martinez in 2015 in South Africa as part of the Rising Star Workshop to study new fossils that eventually led to their first collaboration. Green later corresponded with Dr. Bermudez de Castro while reviewing a related article, and the three connected on this project in late 2019.

“I signed my review (normally, reviews are blind to the authors) and mentioned that I had a large comparative dataset, which could work perfectly for a follow up study,” shared Green. “Dr. Garcia-Martinez had just joined Jose Maria as a post-doc, and the project grew from there.”

The study of shape changes in the shoulder girdle provides critical information about locomotor and behavioral capabilities throughout evolution such as climbing proficiency or the ability to throw objects with precision – stones or spears for hunting or self-defense, for example. One critical component of the shoulder girdle is the shoulder blade or scapula, but the study of these bones has been lacking because the human fossil record contains very few of these delicate fossil bones.

This study, the first attempt to investigate the growth and development of Homo antecessor shoulders, sought to answer: at what stage of human evolution did the shoulder girdle undergo morphological and developmental shifts away from more apelike characteristics seen in earlier hominins?

The team used virtual anthropology tools, 3D geometric morphometry, and complex statistical methods to determine that shoulder development in H. antecessor at ~850,000 years ago was already very similar to that of modern humans, although the growth might have proceeded at a slightly faster rate.

This study indicates at nearly one million years before present, the H. antecessor shoulder girdle was nearly indistinguishable from modern Homo sapiens in both biomechanical capabilities and developmental characteristics. It also highlights shoulder developmental and morphological shift away from behavioral adaptations like climbing, which likely characterized more archaic hominin groups.

“While teaching human anatomy to our healthcare professional students, discussing the evolutionary context of the human body has implications both anatomically and clinically. For example, our evolutionary history has left us with a mobile shoulder joint enabling us to do a wide range of things with our hands: throw with accuracy and power, manipulate objects, and use tools to transform the way we live. With mobility, however, comes a loss of stability, and there are many injuries, both chronic and acute, that we discuss with our students in the context of that anatomy and the evolutionary “baggage” we carry. There are many other examples beyond the shoulder that pertain to functional anatomy, and other examples with cardiovascular, neurological, and embryological or developmental relevance.”