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Study: No Known Hominin is Ancestor of Neanderthals and Modern Humans

Aida Gomez-Robles
GW postdoctoral scientist Aida Gómez-Robles and a team of international scholars studied the teeth of ancient humans to address questions about human evolution.

GW Postdoctoral Scientist Aida Gómez-Robles is Study’s Lead Author

October 21, 2013

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WASHINGTON—The search for a common ancestor linking modern humans with the Neanderthals who lived in Europe thousands of years ago has been a compelling subject for research. But a new study suggests the quest isn’t nearly complete.

Researchers, using quantitative methods focused on the shape of dental fossils, find that none of the usual suspects fits the expected profile of an ancestor of Neanderthals and modern humans. They also present evidence that the lines that led to Neanderthals and modern humans diverged nearly 1 million years ago, much earlier than studies based on molecular evidence have suggested.

The study, which was published today by the Proceedings of the National Academy of Sciences (PNAS), was carried out by an international team of scholars from the George Washington University (GW), Konrad Lorenz Institute for Evolution and Cognition Research in Austria, Indiana University (IU) and Atapuerca Research Team in Spain.

“Our results call attention to the strong discrepancies between molecular and paleontological estimates of the divergence time between Neanderthals and modern humans," said Aida Gómez-Robles, lead author of the paper and a postdoctoral scientist at the Center for the Advanced Study of Hominid Paleobiology in the GW Columbian College of Arts and Sciences. “These discrepancies cannot be simply ignored, but they have to be somehow reconciled.”

P. David Polly, professor in the Department of Geological Sciences in the IU Bloomington College of Arts and Sciences, is a co-author of the study. Other co-authors are Spanish researchers José María Bermúdez de Castro, Juan-Luis Arsuaga and Eudald Carbonell, co-directors of the excavations at Atapuerca sites. The study resulted from a collaboration that developed when Dr. Gómez-Robles spent a semester at IU studying with Dr. Polly while she was a graduate student at the National Research Centre for Human Evolution and at the University of Granada, both in Spain. It also makes use of statistical methods developed by IU Bloomington biologist Emilia Martins.

The article, "No known hominin species matches the expected dental morphology of the last common ancestor of Neanderthals and modern humans," relies on fossils of approximately 1,200 molars and premolars from 13 species or types of hominins—humans and human relatives and ancestors. Fossils from the well-known Atapuerca sites have a crucial role in this research, accounting for more than 15 percent of the complete studied fossil collection.

The researchers use techniques of morphometric analysis and phylogenetic statistics to reconstruct the dental morphology of the last common ancestor of Neanderthals and modern humans. They conclude with high statistical confidence that none of the hominins usually proposed as a common ancestor, such as Homo heidelbergensis, H. erectus and H. antecessor, is a satisfactory match.

“None of the species that have been previously suggested as the last common ancestor of Neanderthals and modern humans has a dental morphology that is fully compatible with the expected morphology of this ancestor,” Dr. Gómez-Robles said.

The study also finds that the potential human ancestors discovered in Europe are morphologically closer to Neanderthals than to modern humans. This suggests the line leading to Neanderthals arose around 1 million years ago and the divergence of humans took place much earlier than previously thought. Other studies have placed the divergence around 350,000 years ago.

The researchers argue that quantitative and statistical methods provide a better way to settle debates about human origins than the descriptive analyses that have been used in the past. "Our primary aim," they wrote, "is to put questions about human evolution into a testable, quantitative framework and to offer an objective means to sort out apparently unsolvable debates about hominin phylogeny." They also suggest applying their methodology to study other body parts represented in the hominin fossil record.

What comes next? Answers to the ancestry question could come from studying hominin fossils from Africa, the researchers said. But the African fossil record from the era of interest is sparse.

“The study tells us that there are still new hominin finds waiting to be made,” Dr. Polly said. “Fossil finds from about 1 million years ago in Africa deserve close scrutiny as the possible ancestor of Neanderthals and modern humans.”

Multimedia Resources Available for Media
The full research paper and figures, including visuals of the teeth studied, are available upon request.

Photos of Aida Gómez-Robles are available upon request.

The Center for the Advanced Study of Hominid Paleobiology
The Center for the Advanced Study of Hominid Paleobiology is a research center at the George Washington University. CASHP’s mission is to undertake strategic research that addresses fundamental problems in human evolution that cross disciplinary boundaries, to act as a catalyst for interdisciplinary research programs involving scientists from other centers around the world and to promote interdisciplinary research through training and education.

The Columbian College of Arts and Sciences
Established in 1821 in the heart of the nation’s capital, the George Washington University Columbian College of Arts and Sciences is the largest of GW’s academic units. It encompasses the School of Media and Public Affairs, the Trachtenberg School of Public Policy and Public Administration and more than 40 departments and programs for undergraduate, graduate and professional studies. The Columbian College provides the foundation for GW’s commitment to the liberal arts and a broad education for all students. An internationally recognized faculty and active partnerships with prestigious research institutions place Columbian College at the forefront in advancing policy, enhancing culture and transforming lives through research and discovery.

The George Washington University
In the heart of the nation’s capital with additional programs in Virginia, the George Washington University was created by an Act of Congress in 1821. Today, GW is the largest institution of higher education in the District of Columbia. The university offers comprehensive programs of undergraduate and graduate liberal arts study, as well as degree programs in medicine, public health, law, engineering, education, business and international affairs. Each year, GW enrolls a diverse population of undergraduate, graduate and professional students from all 50 states, the District of Columbia and more than 130 countries.

Indiana University Bloomington
Indiana University Bloomington is the flagship residential, research-intensive campus of Indiana University. Its academic excellence is grounded in the humanities, arts and sciences and a range of highly ranked professional programs. Founded in 1820, the campus serves more than 42,000 undergraduate and graduate students pursuing degrees in more than 300 disciplines. Widely recognized for its global and international programs, outstanding technology and historic limestone campus, IU Bloomington serves as a global gateway for students and faculty members pursuing issues of worldwide significance.

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