Hominid Evolution in the Omo, as Told by Teeth

From Berkeley, to France, to Ethiopia, 2017 grantees Leslea Hlusko and Jean-Renaud Boisserie explore Hominid evolution across millennia through fossilized teeth.

March 18, 2021
Hominid teeth from the Omo Valley, Ethopia
Hominid teeth from the Omo Valley, Ethopia (Photo by Leslea Hlusko)

For paleontologists, there are few locations as exceptional as the Lower Omo Valley in Ethiopia. Compared to other African sites, which often will not exceed 500,000 years of a continuous fossil record, the Omo Valley truly stands out for its temporal completeness. “The Shungura formation in the Lower Omo Valley was a place where you have a more or less continuous record of evolution in the valley from 3.6, almost 4 million, years ago until one million years ago and even a bit more recent than that,” explains Jean-Renaud Boisserie, Principal Investigator of the Omo Group Research Expedition (OGRE), head of the PALEVOPRIM lab at the University of Poitiers, and senior researcher at CNRS. The OGRE expedition was started in 2006 to revisit the Omo Valley, following the last expedition at that site in 1976. Scientists from all over the world are involved in the project, and they come from a variety of fields, such as archeology, paleontology, and ecology. The lack of gaps in the fossil record for this almost 3 million-year time period allows for researchers to “follow the evolution of the environment, the evolution of the plants, the evolution of the animals, including human ancestors,” says Boisserie.


Searching for fragments of a human tooth
Left: Shungura Formation, Omo Valley; Collecting surface sediments of human tooth fragments (Photo credit: OGRE/J.R. Boisserie)


Even with the exceptional character of the Omo Valley, it is difficult to determine the provenance of fragmentary remains and understand their biology and ecology. Yet, the site contains a large amount of a type of fossil that is extremely useful in this endeavor: teeth.  

Teeth hold a great deal of information about an organism. “The enamel of teeth, laid down over many years while the tooth is developing (from the womb until the age of six or seven for the first adult molar, for example), records chemical information about the individual’s diet and their health. Over much longer time-scales, changes in the shape of teeth between individuals over millions of years tell us how that lineage responded to selective pressures over evolutionary time,” explains Leslea Hlusko, professor in the Human Evolution Research Center and Department of Integrative Biology at UC Berkeley. “The beautiful thing is because [teeth are] so mineralized, they preserve really well in the fossil record.”

Half of Hlusko’s research is on paleontology, while the other half focuses on the genetics of dentition, with expertise in regards to large populations of primates. This combination allows her to “bring this knowledge of how genes make teeth...and apply it to the time depth of the fossil record…[to see] how those mechanisms are evolving through time,” Hlusko explains.

The Omo Valley site contains many teeth of human ancestors, but for a long time, the project lacked experts with a specialty in this particular area. Hlusko was the perfect person to fill that gap. Boisserie and Hlusko, having crossed paths in Ethiopia before, knew of each other’s research, but had never had the chance to work together on a project. In order to fund Hlusko’s involvement—as well as that of Franck Guy, a CNRS researcher who specializes in human ancestors—the team applied to the France-Berkeley Fund. They won a grant in 2017.

“We would never have been able to do this without the France-Berkeley Fund’s support because time in the lab is the most valuable thing to be given as a researcher, and that is what [the FBF] gave us...the time for us to sit together and very deliberately focus on Hominid teeth,” says Hlusko of the grant. Hlusko and Guy together analyzed the vast array of teeth across time, and the changes that occurred in terms of human evolution. This time period covers the beginning of the Genus Homo, as well as another coexisting lineage.

Jean-Renaud Boisserie and Kevin Uno
From left: Collaborator Kevin Uno (Columbia University) and Jean-Renaud Boisserie examine Hominid fossil teeth (Photo by Leslea Hlusko)

Their research on the evolution of teeth within Hominid populations is exploratory, but it has relevance for humans today—for example, in dentistry, to better understand how teeth are made. When someone loses a tooth, their artificial replacement tooth will not be of the same quality as the one they lost. However, with further research available on the evolution of teeth, perhaps one day treatments will be possible to induce humans to grow a new tooth naturally.

Boisserie and Hlusko’s research can also impact our thinking about humans and our environment. In order to conduct research on Hominid evolution, it is important to keep track of our ancestors’ response to environmental changes over millions of years—even if these changes happened at a much slower pace compared to the climate change of today.

“Environmental change is happening so fast that it is impossible for biological evolution to keep up and to respond, and so we either need to way slow down the climate change or we need to really speed up our cultural adaptation --- but [that] is not going to help the other animals,” explains Hlusko. In past eras, several species of humans cohabited with other animals in the same ecosystem, Boisserie adds. Today there is only one species of humans, and we need to reckon with the reality that species of humans in the past have disappeared; the same could happen to Homo sapiens.

At the moment, “we are not thinking as a species. We are thinking in terms of ‘What are my own interests? What are the interests of my country?’” says Boisserie. “I think that paleontologists…[whose work is] showing that we can go extinct, have some good arguments to convince others that we should really start to think as a complete species and to think about what is good for homo sapiens and our offspring in the future.”

If the future of the species is a difficult topic to ponder, on a smaller scale, Boisserie and Hlusko are planning for the future of their collaboration. Their initial project focused on the Omo Valley, but they aim to use their framework to expand the research to other sites. They plan to leverage the data from their France-Berkeley project to apply for a grant from the European Research Council next fall.

As for their advice for future FBF applicants? “If at first you don’t succeed, keep trying...it was the third application that we put in that was funded,” says Hlusko.

“The funding from the France-Berkeley Fund was great for us. We are really thankful for the ability to develop that research, and I think it will go much further,” adds Boisserie.