3-D Labyrinthine Computerized Tomography Tracks Human Dispersal Across the Globe

Little do audiologists know that based upon a 2018 study, the labyrinth can now be used by paleontologists to trace the movement of humans across the globe thousands of years ago.   

There are two theories about how humans populated the world.  The Multi-regional hypotheses, first proposed in the 1980s and revised in 2003, suggests that erectus left Africa some 2 million years ago and simply evolved anatomically into modern humans. This theory suggests that the Neanderthals, Denisovans and heidelbergensis were all simply regional variants of the same species that evolved into modern Homo sapiens.  Proponents of multiregionalism point to fossil and genomic data and continuity of archaeological cultures as support for their hypothesis.  According to Hist (2018), the multiregional theory is largely discredited in favor of the Out of Africa Theory. 

Our species, Homo sapiens is an African one; Africa is where we first evolved, and where we have spent the majority of our time on Earth. The earliest fossils of recognized as modern Homo sapiens appear in the fossil record at Omo Kibish in Ethiopia, around 200,000 years ago. Although earlier fossils may be found over the coming years, this is paleontology’s best understanding of when and approximately where we originated.  The Out of Africa hypothesis suggests that anatomically modern humans originated in Ethiopian Africa and begun to emigrate around the world somewhere between 120,000 – 60,000 years ago. It suggests that when modern humans spread throughout the planet they replaced the other hominin groups. Genetic evidence over the last decade has provided greater support for this Out of Africa theory, making it the predominate thought on how humans dispersed to various parts of the globe. Discussing the Out of Africa Theory, Himme (2018) summarizes that “current evidence suggests anatomically modern Homo sapiens left Africa as early as 120,000 years ago, and by 50,000 years ago had reached Australia.”  Evidence suggests there may have only been a single exodus from Africa and that probably only a few hundred people were involved. “Himme further summarizes that, “between 40,000 and 12,000 years ago, humans moved north into Europe. However, their range was limited by an ice sheet that extended into the northern part of continental Europe. The colder temperatures at this time also meant sea levels were much lower and America and Asia were connected by a land bridge, eventually allowing people access into America. Humans initially followed the coastline and rivers, probably because they were easier to navigate than the densely forested mainland and fishing may have offered a stable food source.”

Paleontology and the Inner Ear

Unraveling the first migrations of anatomically modern humans out of Africa has invoked great interest among researchers from a wide range of disciplines. Available fossil, archeological, and climatic data offer many hypotheses, and as such, modern genome-wide genotyping and sequencing techniques as well as an increase in the availability of ancient samples, offers another important tool for testing theories relating to our own history. Now for the first time another method of reviewing human dispersal is available to paleontologists as the work to solve this mystery.  In the past, morphological data from the skull and skeleton were used to track human dispersal across the globe but examination of these remains often only allow only limited conclusions about the geographical dispersal pattern das the human skeleton tends to adapt to local environmental conditions. Now, an international team of researchers led by paleoanthropologists from the University of Zurich, Marcia Ponce de Leon and Prof. Dr. Christoph Zollikofer have demonstrated that the morphology of the inner ear is a good indicator for population history and human dispersal.  According to their research,  slight differences can be found in the inner ear of different populations of modern humans (Homo sapiens) and paleoanthropologists can use these differences to provide more reliable information about the global dispersal of humans from Africa.   The hearing and balance system in humans, as in all vertebrates, is housed in a cavity system in the base of the skull — the bony labyrinth of the inner ear. Ponce de Leon and Zollikofer analyzed the labyrinth structures in human populations from southern and northern Africa, Europe, Asia, Australia, and America, including as far south as Patagonia, using computed tomography to obtain high-resolution 3-D data of the bony labyrinth. Ponce de Leon et al (2018) explains that, “The cavity system of the inner ear (the so-called bony labyrinth) is a good candidate structure for such analyses. It is already fully formed by birth, which minimizes postnatal phenotypic plasticity, and it is generally well preserved in archaeological samples. Here we use morphometric data of the bony labyrinth to show that it is a surprisingly good marker of the global dispersal of modern humans from Africa. Labyrinthine morphology tracks genetic distances and geography in accordance with an isolation-by-distance model with dispersal from Africa. Our data further indicate that the neutral-like pattern of variation is compatible with stabilizing selection on labyrinth morphology. Given the increasingly important role of the petrous bone for ancient DNA recovery from archaeological specimens, we encourage researchers to acquire 3D morphological data of the inner ear structures before any invasive sampling. Such data will constitute an important archive of phenotypic variation in present and past populations, and will permit individual-based genotype–phenotype comparisons.”  The team’s data showed that the 3-D shape of the labyrinth varied greatly and contained important information about the global dispersal of humans from the African continent.   Thus, their finding were that the further away the population was geographically from South Africa, the more the shape of the labyrinth differs from that of the South African population. Moreover, the labyrinth data confirm the findings from DNA analyses which show that the genetic distance increases in correlation with the geographical distance from Africa.

 

References:

Gugliotta, G. (2008). The Great Human Migration.  Smithsonian Magazine.  Retrieved April 5, 2018.

Hirst, K. (2018).  Multiregional Hypothesis: Human Evolutionary Theory:  A Now-Discredited Theory of Human Evolution.  ThoughtCo.  Retrieved April 4, 2018.

Himme, B. (2018). The spread of modern humans.  Pathwayz:  Dispersal of modern humans.  Retrieved April 5, 2018.

Ponce de Leon, M. & Zollikofer, C. (2018). Inner ear provides clues to human dispersal. Science News.  Retrieved April 5, 2018.

Ponce de Leon, M., Koesbardiati, T., Weissmann, J., Milella, M., Reyna-Blanco, C., Suma, G., Malaspinas, A., White, T., & Zollikofer, C. (2018). Human boney labyrinth is an indicator of population history and dispersal from Africa.  Proceedings of the National Academy of Sciences, Retrieved April 9, 2018.

About Robert Traynor

Robert M. Traynor, Ed.D., MBA is the CEO and practicing audiologist at Audiology Associates, Inc., in Greeley, Colorado with particular emphasis in amplification and operative monitoring, offering all general audiological services to patients of all ages. Dr. Traynor holds degrees from the University of Northern Colorado (BA, 1972, MA 1973, Ed.D., 1975), the University of Phoenix (MBA, 2006) as well as Post Doctoral Study at Northwestern University (1984). He taught Audiology at the University of Northern Colorado (1973-1982), University of Arkansas for Medical Sciences (1976-77) and Colorado State University (1982-1993). Dr. Traynor is a retired Lt. Colonel from the US Army Reserve Medical Service Corps and currently serves as an Adjunct Professor of Audiology at the University of Florida, the University of Colorado, and the University of Northern Colorado. For 17 years he was Senior International Audiology Consultant to a major hearing instrument manufacturer traveling all over the world providing academic audiological and product orientation for distributors and staff. A clinician and practice manager for over 35 years, Dr. Traynor has lectured on most aspects of the field of Audiology in over 40 countries. Dr. Traynor is the current President of the Colorado Academy of Audiology and co-author of Strategic Practice Management a text used in most universities to train audiologists in practice management, now being updated to a 2nd edition.

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