Discoveries Unveil Two Ancient Human Ancestors Coexisting: Could One Be an Unknown Species?

Fossilized teeth found in northeastern Ethiopia reveal that two types of early human ancestors, or hominins, existed at the same time, around 2.6 to 2.8 million years ago. Notably, one type may be a new species. This discovery, published in the journal Nature, sheds light on how human evolution is more complex than we thought.

Among the teeth, ten belonged to the genus Australopithecus, known for its upright walking, while three were from the genus Homo, which includes modern humans. Typically, scientists believed that Homo appeared after Australopithecus. However, this overlap challenges that idea, suggesting that multiple hominin species coexisted. Kaye Reed, the study’s coauthor and an expert at Arizona State University, emphasized that human evolution is not a straight line, but rather resembles a bushy tree with many branches, some of which went extinct.

The discovery contributes to the ongoing research led by Reed since 2002, focusing on early Homo species under the Ledi-Geraru Research Project. Previous findings from this project include the oldest known Homo jawbone, dating back 2.8 million years. Despite this, evidence for Australopithecus afarensis, a species that existed 3.9 million years ago, hasn’t appeared in the fossil record after about 2.95 million years ago.

The most famous representative of Australopithecus afarensis is Lucy, who lived around 3.2 million years ago. She stood about 3.3 feet tall and exhibited a mix of humanlike and apelike features.

When Reed and her team found the Australopithecus teeth in separate excavations during 2018 and 2020, they realized these teeth were distinct from known species. They likely belong to a previously unknown species of Australopithecus. Reed noted that they initially thought they would only find Homo specimens, but the Australopithecus teeth changed that narrative.

The findings come from the Afar region, a crucial area for human evolution studies. The Afar is known for uncovering early fossils and stone tools. Geological activity in the region, which involves tectonic plates pulling apart, exposes older sediment layers that provide insight into nearly 5 million years of evolution.

Reed explained that when the teeth were dated, the Australopithecus samples dated to 2.63 million years ago, while the Homo teeth dated to between 2.59 and 2.78 million years ago. However, more data and fossils are needed before conclusively identifying the species from these teeth.

Dr. Stephanie Melillo, a paleoanthropologist, emphasized the importance of this study as it sheds light on a tricky period in human evolution. Much of the challenge lies in the layers of sediment that have built up over time, limiting fossil discoveries. Areas like the Turkana Basin have previously provided evidence of coexistence among different species, but this new discovery in the Afar shows that Australopithecus thrived alongside Homo.

Interestingly, the environmental conditions during this time were different from today’s. The Afar region used to experience seasonal rainfall variations, creating wetlands and grasslands. Reed proposed that understanding what both hominins ate could illuminate their interactions—whether they competed for resources or shared them. Additionally, researchers hope to determine which of the hominins made the stone tools found nearby.

As Reed put it, “Whenever there’s an exciting discovery, we always know we need more information.” The quest for fossils continues to fill in the gaps in our understanding of human history. Every find is a step closer to uncovering the complex story of our origins.

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