This facial reconstruction represent a male individual of Homo georgicus (from the Dmaisi excavation). Credit: Cicero Moraes et alii (Luca Bezzi, Nicola Carrara, Telmo Pievani) via Wikimedia. CC BY 4.0

The textbook version of the "Out of Africa" hypothesis holds that the first human species to leave the continent around 1.8 million years ago was Homo erectus. But in recent years, a debate has emerged suggesting it wasn’t a single species, but several. New research published in the journal PLOS One now hopes to settle the matter once and for all.

The debate centers on the Dmanisi fossils, five skulls found in the Republic of Georgia between 1999 and 2005, which belong to some of the oldest humans ever found outside Africa. The problem is that they don’t look alike. Some are larger than others, particularly Skull 5, which has a tiny braincase but a massive, protruding face. Some researchers explain this as a difference in sexes within the same species, while others argue that it represents two distinct species living together.

Ancient teeth

To provide much-needed clarity, researchers led by Victor Nery at the University of São Paulo studied the teeth of three Dmanisi specimens. The reason is that, generally, skulls are not always the best species identifiers because bone is fragile and can be warped and crushed. Dentition is far more useful because enamel is the hardest biological substance produced by humans, and everything from the shape and size of individual teeth can be used to identify a species.

Morphological affinities of Dmanisi compared to other hominin species based on the first two discriminant functions calculated from maxillary dentition areas. Credit: PLOS One (2025). DOI: 10.1371/journal.pone.0336484

The team focused on the surface area (dental crown) of the back teeth (premolars and molars) of the Dmanisi specimens that had sufficient dental remains for analysis. They compared these to a database of 122 other fossil specimens, including Australopithecus and several other Homo species. Then, using a statistical sorting tool, they analyzed 583 teeth to create a biological map and determine whether the Dmanisi fossils belonged to a single family or to other branches of our family tree.

Two species instead of one?

The map revealed that these ancient remains were not from a single group. Skull 5, with its large jaw, was grouped with Australopiths, a more primitive ape-like ancestor. The other two specimens were more human-like. Because of this, the study authors support using the names Homo georgicus for Skull 5 and Homo caucasi for the human-like group.

To ensure the differences weren’t just between males and females, the team compared the fossils with those of great apes. In some animals, like gorillas, males are much larger than females but still have the same basic teeth. The differences between the Dmanisi teeth were so great that male-female differences within the same group couldn’t explain them.

"The postcanine dental crown area analysis of the Dmanisi hominin fossils... supports the hypothesis of distinct species coexisting temporally at the site (Homo caucasi and Homo georgicus). This possibility challenges the prevailing model of Homo erectus migration out of Africa..." commented the researchers in their paper.

While the research lends weight to the idea that two species left Africa at roughly the same time, more specimens may be needed before a consensus is reached.

Written for you by our author Paul Arnold, edited by Gaby Clark, and fact-checked and reviewed by Robert Egan—this article is the result of careful human work. We rely on readers like you to keep independent science journalism alive. If this reporting matters to you, please consider a donation (especially monthly). You’ll get an ad-free account as a thank-you.

More information: Victor Nery et al, Testing the taxonomy of Dmanisi hominin fossils through dental crown area, PLOS One (2025). DOI: 10.1371/journal.pone.0336484

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Citation: Two ancient human species came out of Africa together, not one, suggests new study (2025, December 22) retrieved 22 December 2025 from https://phys.org/news/2025-12-ancient-human-species-africa.html

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