By Madeline Reinsel

Family trees can be complicated for modern humans. New research from Virginia Commonwealth University paleoecologist Amy Rector and colleagues finds that our species’ forebears are no exception.

For many years, scientists thought the genus Homo, which includes today’s humans, evolved directly out of the genus Australopithecus, of Lucy fossil fame. More recently, paleoanthropologists have found fossils that suggest that early Homo species lived alongside other hominins – or upright-walking apes – from at least two additional genera, or groups of species.

“Most people, when they envision human evolution, think of that typical march of progress, where one species evolves into the next species evolves into the next,” said Rector, Ph.D., an associate professor of anthropology in VCU’s School of World Studies. “And the more that paleoanthropologists are out there and looking for fossils, the more we’re finding that that is not an accurate representation of the evolution of our lineage.”

Now, ancient teeth discovered in recent years by Rector and colleagues at the Ledi-Geraru Research Project in Ethiopia have revealed a new species of Australopithecus that lived alongside early members of the Homo genus 2 million to 3 million years ago.

“What we found during that time period are two different species living at the same time, potentially sharing space and time, evolving at the same time, really showing us that human evolution has been much more of this kind of bushy tree,” said Rector, who is the co-director of the Ledi-Geraru Research Project.

The team’s next step is to analyze the teeth’s enamel to find out what the new species might have been eating millions of years ago. VCU News spoke with Rector to find out more about this discovery.

Let’s talk about your study site. Why are there so many fossils there, and how do you collect them?

Our study site is the Ledi-Geraru Research Project permit area in northern Ethiopia’s Afar Region. It’s close to other well-known paleoanthropological sites like Hadar, where Lucy was found. All of these sites in the Afar Region are great places to discover fossils because they are within the northern range of the East African Rift Valley. That’s where large tectonic plates under Earth’s surface are pulling apart and exposing deeper and older layers under the ground, revealing the fossils of animals that lived and died several million years ago.

We work with the geologists on our team to find the areas where we want to search, and then we go to the areas that we know are exposing this time period and strategically and systematically walk the surface looking for fossils. When we find them, we collect all the location data and photos for our database, and then all the fossils are stored at the National Museum of Ethiopia.

What period of human evolution did you explore in this study?

Our team is especially interested in the time period between about 2 million and 3 million years ago, when our lineage, the genus Homo, first evolved, when Lucy’s species went extinct and which is very rarely preserved in other paleoanthropological sites. The Ledi-Geraru area is amazing in that it does preserve this time period, so almost every discovery we make is a new one.

Tell us about finding the teeth.

I was lucky enough to be involved in the discovery of several of the teeth that we describe in the paper, alongside our Afar colleagues, Omar Abdulla and Mohammed Ahmeddin, as well as Kaye Reed from Arizona State University.

That morning in 2018, we were walking and finding fossils on a small hill near the eastern boundary of the basin. We were so excited when Omar found the first tooth, a premolar. We knew it was a hominin tooth – from the mouth of one of our ancestors – and I think it was the first hominin found that season. We eventually found five teeth from the same mouth – all molars that fit together and looked not so different from our own teeth.

It took years of study to determine that the teeth represent a new species of Australopithecus. How does that change our understanding of human evolution?

This means that our family tree is a lot bushier than we previously thought. We already know that there were multiple species of Australopithecus, sometimes alive at the same time, and now we have added another species that is close in time and space to the earliest member of our own genus, Homo. 

We know now, especially after this new discovery, that the process of hominin evolution was one of great experimentation, with many different species adapting to different resources and climatic conditions in many ways, potentially at the same or similar times. It’s tantalizing and exciting evidence that competition was an important part of our evolution. It’s also such clear evidence of the importance of continued field work – there are more discoveries, especially from this time period, to make.

What does it mean if Homo and Australopithecus lived in the same region at the same time?

It’s so exciting to find evidence that these two genera may have overlapped in the Afar Region. As a paleoecologist, one of my primary research questions is investigating the climatic contexts of our earliest ancestors: What did the world look like when our ancestors woke up in the morning? What kinds of habitats and resources did they need?

And knowing that multiple genera like Homo and Australopithecus may have nearly overlapped in time and space means that they were likely able to take advantage of similar habitats, and that this region was especially important for the evolution of the lineage that eventually led to our species and what it means to be human. The more discoveries we make, the more detailed understanding we can have as to where in space and time these species were really existing and adapting, and what that means for how our lineage has responded to climate change and seasonality over time. 

You mentioned two Afar colleagues earlier, both of whom died in recent years. Tell us about them.

Omar Abdulla Omar was from the Hadar district in the Afar Region and began working with members of the Ledi-Geraru Research Project team on the Hadar Field Project decades ago. He then became a critical team member when the Ledi-Geraru Research Project was launched by Kaye Reed, Ramon Arrowsmith and Charlie Lockwood in 2001. Omar died during the Ethiopian Civil War in 2022. Mohammed Ahmeddin Hayidara was a deeply respected representative of the Afar government who often accompanied paleoanthropological projects. He was a font of knowledge about Afar culture, a skilled translator and was a talented fossil finder. Mohammed spent many years working with the Ledi-Geraru Research Project. He died in 2024.