Ancient Teeth Challenge Out of Africa single Species

Two Ancient Human Species Left Africa Together, Not One, New Study Suggests

Rethinking the Traditional "Out of Africa" Narrative

The traditional account of the "Out of Africa" hypothesis suggests that Homo erectus was the first human species to leave Africa around 1.8 million years ago. In recent years, however, scientists have questioned whether this migration involved just one species or several. A new study published in PLOS One aims to resolve the debate.

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The Dmanisi Fossils at the Centre of the Debate

At the heart of the discussion are the Dmanisi fossils — skulls 5 discovered in Georgia between 1999 and 2005 — among the ancient human remains found outside Africa.

The challenge lies in their striking differences: some skulls are notably larger than others, particularly Skull 5, which combines a very small braincase with a large, projecting face.

While some researchers interpret these contrasts as differences between males and females of a single species, others argue they point to two separate species living side by side.

Ancient Teeth Offer New Clues

Why Teeth Matter More Than Skulls

To bring much-needed clarity to the debate, researchers led by Victor Nery at the University of São Paulo turned their attention to the teeth of three Dmanisi specimens.

Skulls are not always reliable indicators of species, as bone is fragile and can become distorted or crushed over time. Teeth, by contrast, offer a stronger line of evidence: enamel is the hardest substance produced by the human body, and the size and shape of individual teeth can reveal crucial clues about species identity.

The team examined the surface area of the back teeth — specifically the premolars and molars — from Dmanisi fossils that were sufficiently preserved for study. These measurements were compared with a database of 122 other fossils specimens, including Australopithecus and several memebers of the genus Homo.

Mapping the Human Family Tree

Using a statistical sorting method, the researchers analyzed 583 teeth to build a biological map and assess whether the Dmanisi fossils belonged to a single lineage or represented different branches of the ancient human family tree.

The results were clear: the remains did not belong to a single group.

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Two Species Instead of One?

A Clear Divide in the Fossil Record

The biological map made one conclusion clear: the ancient remains did not belong to a single group. Skull 5, distinguished by its powerful jaw, clustered with australopiths — a more primitive, ape-like branch of our ancestry. The remaining two specimens displayed more recognizably human traits.

On this basis, the researchers support classifying:

• Skull 5 as Homo georgicus
• More human-like fossils to Homo caucasi

This interpretation directly challenges the long-held view that Homo erectus alone drove the first migration out of Africa.

Why Gender Differences Cannot Explain the Findings

To rule out simple gender-based differences, the team compared the fossils with those of modern great apes. In species such as gorillas, males are significantly larger than females, yet their teeth remain fundamentally similar. The variation seen in the Dmanisi teeth was far too pronounced to be explained by male-female differences within a single species.

Analysis of the postcanine dental crown surfaces in the Dmanisi hominin fossils, the researchers write, supports the idea that two distinct species —  Homo caucasi and Homo georgicus — were living at the site at the same time. This interpretation directly challenges the long-standing view that Homo erectus alone was responsible for the first migration out of Africa.

What This Means for Human Evolution

Although the findings strengthen the case for multiple species leaving Africa around the same period, the authors note that additional fossil evidence will be needed before the debate can be conclusively settled.

Understanding humanity's evolutionary past also informs modern perspectives on health, biology and human adaptability — themes frequently explored on Human Health Issues, which links ancient biology to present-day human development.

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