A new fossil face sheds light on early migrations of ancient human ancestor

A 1.5-million-year-old fossil from Gona, Ethiopia reveals new details about the first hominin species to disperse from Africa.

Midwestern University

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Map showing potential migration routes of the human ancestor, Homo erectus, in Africa, Europe and Asia during the early Pleistocene. Key fossils of Homo erectus and the earlier Homo habilis species are shown, including the new face reconstruction of the DAN5 fossil from Gona, Ethiopia dated to 1.5 million years ago.

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Credit: Dr. Karen L. Baab. Scans provided by National Museum of Ethiopia, National Museums of Kenya and Georgian National Museum.

 

A 1.5-million-year-old fossil from Gona, Ethiopia reveals new details about the first hominin species to disperse from Africa.

Summary: Virtual reassembly of teeth and fossil bone fragments reveals a beautifully preserved face of a 1.5-million-year-old human ancestor—the first complete Early Pleistocene hominin cranium from the Horn of Africa. This fossil, from Gona, Ethiopia, hints at a surprisingly archaic face in the earliest human ancestors to migrate out of Africa.

Publication: Nature Communications (https://www.nature.com/articles/s41467-025-66381-9)

 

A team of international scientists, led by Dr. Karen Baab, a paleoanthropologist at the College of Graduate Studies, Glendale Campus of Midwestern University in Arizona, produced a virtual reconstruction of the face of early Homo erectus. The 1.5 to 1.6 million-year-old fossil, called DAN5, was found at the site of Gona, in the Afar region of Ethiopia. This surprisingly archaic face yields new insights into the first species to spread across Africa and Eurasia. The team’s findings are being published in Nature Communications.

According to Dr. Baab, “We already knew that the DAN5 fossil had a small brain, but this new reconstruction shows that the face is also more primitive than classic African Homo erectus of the same antiquity. One explanation is that the Gona population retained the anatomy of the population that originally migrated out of Africa approximately 300,000 years earlier.”

Gona, Ethiopia

The Gona Paleoanthropological Research Project in the Afar of Ethiopia is co-directed by Dr. Sileshi Semaw (Centro Nacional de Investigación sobre la Evolución Humana, Spain) and Dr. Michael Rogers (Southern Connecticut State University). Gona has yielded hominin fossils that are older than 6.3 million years ago, and stone tools spanning the last 2.6 million years of human evolution. The newly presented hominin reconstruction includes a fossil brain case (previously described in 2020) and smaller fragments of the face belonging to a single individual called DAN5 dated to between 1.6 and 1.5 million years ago. The face fragments (and teeth) have now been reassembled using virtual techniques to generate the most complete skull of a fossil human from the Horn of Africa in this time period. The DAN5 fossil is assigned to Homo erectus, a long-lived species found throughout Africa, Asia, and Europe after approximately 1.8 million years ago.

How did the scientists reconstruct the DAN5 fossil?

The researchers used high-resolution micro-CT scans of the four major fragments of the face, which were recovered during the 2000 fieldwork at Gona. 3D models of the fragments were generated from the CT scans. The face fragments were then re-pieced together on a computer screen, and the teeth were fit into the upper jaw where possible. The final step was “attaching” the face to the braincase to produce a mostly complete cranium. This reconstruction took about a year and went through several iterations before arriving at the final version.

Dr. Baab, who was responsible for the reconstruction, described this as “a very complicated 3D puzzle, and one where you do not know the exact outcome in advance. Fortunately, we do know how faces fit together in general, so we were not starting from scratch.”

What did scientists conclude?

This new study shows that the Gona population 1.5 million years ago had a mix of typical Homo erectus characters concentrated in its braincase, but more ancestral features of the face and teeth normally only seen in earlier species. For example, the bridge of the nose is quite flat, and the molars are large. Scientists determined this by comparing the size and shape of the DAN5 face and teeth with other fossils of the same geological age, as well as older and younger ones. A similar combination of traits was documented previously in Eurasia, but this is the first fossil to show this combination of traits inside Africa, challenging the idea that Homo erectus evolved outside of the continent. “I'll never forget the shock I felt when Dr. Baab first showed me the reconstructed face and jaw,” says Dr. Yousuke Kaifu of the University of Tokyo, a co-author of the study.

“The oldest fossils belonging to Homo erectus are from Africa, and the new fossil reconstruction shows that transitional fossils also existed there, so it makes sense that this species emerged on the African continent,” says Dr. Baab. “But the DAN5 fossil postdates the initial exit from Africa, so other interpretations are possible.”

Dr. Rogers agrees. “This newly reconstructed cranium further emphasizes the anatomical diversity seen in early members of our genus, which is only likely to increase with future discoveries.”

“It is remarkable that the DAN5 Homo erectus was making both simple Oldowan stone tools and early Acheulian handaxes, among the earliest evidence for the two stone tool traditions to be found directly associated with a hominin fossil,” adds Dr. Semaw.

Future Research

The researchers are hoping to compare this fossil to the earliest human fossils from Europe, including fossils assigned to Homo erectus but also a distinct species, Homo antecessor, both dated to approximately one million years ago. "Comparing DAN5 to these fossils will not only deepen our understanding of facial variability within Homo erectus but also shed light on how the species adapted and evolved," explains Dr. Sarah Freidline of the University of Central Florida, study co-author.

There is also potential to test alternative evolutionary scenarios, such as genetone to two million years ago to sort this out.”

Virtual reconstruction of fossil face of 1.5 million-year-old human ancestor

Caption

Fossil fragments of a face as well as teeth were reassembled to produce the most complete cranium of a human ancestor from this time in the Horn of Africa.

Credit

Dr. Karen L. Baab. Scans provided by National Museum of Ethiopia. Photographs courtesy of M. Rogers and G. Suwa.

Photo montage of five major elements of DAN5 fossil cranium.Photo montage of five major elements of DAN5 fossil cranium.

Credit

Dr. Michael Rogers

Phone: +1 (623) 572-3737

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Journal

Nature Communications

DOI

10.1038/s41467-025-66381-9 

Method of Research

Computational simulation/modeling

Subject of Research

Not applicable

Article Title

“New reconstruction of DAN5 cranium (Gona, Ethiopia) supports complex emergence of Homo erectus”

Article Publication Date

16-Dec-2025

Contrails are a major driver of aviation’s climate impact

Chalmers University of Technology

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Aviation’s climate impact extends beyond carbon dioxide emissions. A new study from Chalmers University of Technology and the University of Gothenburg, Sweden, and Imperial College, UK, reveals that contrails can represent a significant portion of aviation’s overall climate cost. The study also shows that climate impact can be reduced by optimising flight routes.

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Credit: Wikimedia Commons, CC BY-SA 2.5 | André Karwath

Aviation’s climate impact extends beyond carbon dioxide emissions. A new study from Chalmers University of Technology and the University of Gothenburg, Sweden, and Imperial College, UK, reveals that contrails can represent a significant portion of aviation’s overall climate cost. The study also shows that climate impact can be reduced by optimising flight routes.

In a new article in Nature Communications, The social costs of aviation CO₂ and contrail cirrus, the researchers demonstrate that both CO₂ emissions and contrail formation contribute materially to aviation’s climate impact – and that the associated societal costs differ substantially depending on weather patterns and routing decisions. They find that, at the global level, contrails account for about 15 percent of aviation’s climate impact when measured in economic terms.

After also analysing nearly half a million flights across the North Atlantic, the research team has generated new insights that can support both industry and policymakers in guiding aviation towards more climate optimal operations. Drawing on extensive flight and meteorological data, in combination with a contrail model and an advanced climate-economy model, the researchers estimated the climate and societal cost attributable to each emission source.

“Our research provides a basis for strategies to reduce the climate impact of contrails. Our calculations can be used for optimisation of flight routes where climate impact is considered alongside, for example, fuel cost and travel time. The results give airline operators and air traffic management new tools for climate optimisation. This could bring significant climate and societal benefits,” says Susanne Pettersson, postdoctoral researcher at the Department of Space, Earth and Environment at Chalmers.

The study shows that 38 percent of flights generate contrails that have a warming effect. It also shows that it would be beneficial from a climate perspective to reduce the formation of contrails of almost all these flights through minor rerouting, to avoid contrail formation, even if this results in slightly higher carbon dioxide emissions.

“The new knowledge also provides a foundation for designing new regulations and policy instruments to reduce aviation’s climate impact. The European Commission is currently working on proposals to steer aviation towards lower climate impact, and our new study can hopefully support this process,” says Daniel Johansson, associate professor at the Department of Space, Earth and Environment at Chalmers and one of the lead authors of the next IPCC climate report.

Learn more on contrails, aviation and climate change: Read an article written by the researchers as a Resources For the Future (RFF) issue in brief.

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Journal

Nature Communications

DOI

10.1038/s41467-025-64355-5 

Method of Research

Data/statistical analysis

Subject of Research

Not applicable

Article Title

The social costs of aviation CO₂ and contrail cirrus

Study documents potentially hazardous flame retardants in firefighter gear

Study documents potentially hazardous flame retardants in firefighter gear

Duke University

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Some firefighter gear is manufactured with chemicals called brominated flame retardants that could pose a risk to firefighter health, according to a new study published in Environmental Science & Technology Letters on Dec. 16.

The study is the first published research in the U.S. to investigate and document the use of brominated flame retardants in firefighter turnout gear, worn for protection on the job. The findings could inform fire department decision-making when it comes to keeping or replacing gear.

Structural firefighters — those working in the built environment — wear turnout gear consisting of three layers: a flame-resistant outer shell; a middle layer, called a moisture barrier, that shields against germs while providing breathability; and an inner layer to prevent overheating.

These protective qualities stem in part from chemical treatments added to the garments by manufacturers to meet rigorous standards developed by the National Fire Protection Association, according to lead author Heather Stapleton, Ronie-Richele Garcia-Johnson Distinguished Professor at Duke University’s Nicholas School of the Environment.

For several years, firefighters have been concerned about turnout gear treatments containing chemicals called PFAS, which confer oil and water resistance and sometimes flame resistance. Multiple human and animal studies have found associations between PFAS exposures and various health problems, including some cancers.

Although no studies have directly linked use of PFAS in turnout gear exposure to subsequent health risks in firefighters, gear manufacturers have been phasing out use of the chemicals. Additionally, several states have passed legislation that will prohibit the purchase of turnout gear treated with PFAS starting in 2027.

These actions have prompted questions about what other substances manufacturers might use in turnout gear. Companies do not typically disclose chemical ingredients in their treatments.  

“There was a rumor that one of the turnout gear manufacturers might be using brominated flame retardants in the non-PFAS treated textiles,” Stapleton said. “Because some brominated flame retardants have known toxicity, I requested a sample of the gear in question to test.’”

Brominated flame retardants are added to textiles and other products to reduce flammability. Exposure to the chemicals has been associated with negative health effects including cancer, thyroid disease and neurodevelopmental problems.

Stapleton’s informal experiment found evidence of brominated flame retardants in the turnout gear sample, spurring a more robust study with partners at North Carolina State University’s Wilson College of Textiles and the International Association of Fire Fighters. Their aim was to better understand the occurrence of PFAS and brominated flame retardants in gear manufactured in different years.

Peeling Back the Layers

The researchers collected nine sets of used turnout gear produced between 2013 and 2020, and three sets from 2024 that were marketed as non-PFAS treated. Using two types of analyses, they tested each layer of gear for PFAS and brominated flame retardants. The analyses enabled them to determine the total amount of chemicals in the gear and the amounts that might rub off during wear — what they called “extractable” levels.

“We wanted to know which chemicals were intentionally applied during manufacturing, and we wanted to know what was likely to leach out over time, which could raise the risk of exposure through skin absorption or inhalation,” Stapleton said. 

As expected, the team detected PFAS in all sets of turnout gear manufactured between 2013 and 2020. However, turnout gear made in 2024 contained only low or non-detectable levels of extractable PFAS, indicating that the garments had not been treated with the chemicals, as the manufactures had indeed advertised. Rather, those minor amounts had likely glommed onto the garments from the surrounding environment during use, the authors noted.

Each set of turnout gear also showed evidence of brominated flame retardants, at extractable levels generally greater than those measured for PFAS.

The highest extractable concentrations of brominated flame retardants occurred in garments advertised as non-PFAS treated, especially in the moisture barrier. The finding suggests that manufacturers intentionally added brominated flame retardants to help pass the flammability standard, and likely to compensate for the loss of a certain PFAS previously used in moisture barriers, Stapleton said.

Of the brominated flame retardants identified, a chemical called decabromodiphenyl ethane, or DBDPE, occurred at the greatest extractable levels.

Although no studies have examined the health effects of DBDPE exposure in the U.S., according to the team, a 2019 study of workers at a chemical manufacturing plant in China found associations between exposure to DBDPE, changes in thyroid hormone levels and signs of thyroid disease.

“I was really surprised that the manufacturers used DBDPE in turnout gear,” Stapleton said. “It has similar properties as a toxic chemical called decaBDE that has been largely phased out globally, raising questions about its safety.”

For most of the turnout gear manufactured between 2013 and 2020, the outer shell contained greater extractable concentrations of brominated flame retardants than either the moisture barrier or the inner lining, likely reflecting accumulation from exposure to soot and smoke associated with fires, according to Stapleton.

“When building materials burn, they can release brominated flame retardants into the air that stick to gear and don’t wash out very well,” she explained.

However, the presence of brominated flame retardants in internal layers indicates that some manufacturers had been using these chemicals in turnout gear treatments for years, before PFAS were phased out of gear treatments, according to the authors.

Weighing the Costs

Although firefighters’ specific exposure levels to these chemicals and the potential associated health effects have yet to be established, fire departments now have new data to consider when evaluating gear.

“Turnout gear is really expensive — one set costs thousands of dollars — and firefighters often use these garments for many years. Fire departments must consider both the financial and personal safety costs of keeping or replacing gear,” said coauthor R. Bryan Ormond, an associate professor at the Wilson College of Textiles and director of NC State’s Milliken Textile Protection and Comfort Center, who has studied trade-offs in gear performance.

According to Stapleton, some turnout gear suppliers have pivoted and are now selling garments untreated with PFAS or brominated flame retardants. To that end, she suggests fire departments advocate for more transparency about the chemical treatments used.

“We know firefighters receive higher exposure to multiple chemicals from all the hazards they face during their duty, and they shouldn’t have to worry about receiving additional chemical exposures from their gear,” said Stapleton, who also leads a study on cancer incidence in firefighters. “These first responders are a critically important component of our public safety and deserve to be respected and protected.”

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Funding: This project was supported by the North Carolina Collaboratory at the University of North Carolina at Chapel Hill, with funding appropriated by the North Carolina General Assembly (to HMS and BO). HMS also wishes to thank Michael and Annie Falk for establishing the Falk Exposomics Laboratory.

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Journal

Environmental Science & Technology