A new study examining ancient hominin fossils from Georgia is calling into question long-held views on human origins, suggesting the remains may represent not one, but two early human species.
The research, led by Victor Nery from the University of São Paulo and published in PLOS One, points to distinct physical differences in the fossils that go beyond what would be expected from variation within a single species.
The Dmanisi site, dated to around 1.8 million years ago, has produced some of the earliest known human fossils outside Africa. These remains were traditionally grouped under Homo erectus, but researchers have debated the noticeable variation in skull and jaw structure since their discovery.
The new analysis shifts the focus from skulls to teeth, revealing that differences in dental crown area among three individuals suggest the presence of two separate hominin groups.
Teeth reveal key differences in early hominins
Nery’s team studied over 500 fossil teeth using statistical models to compare dental measurements across 15 ancient human species.
The results showed that two of the Dmanisi individuals had teeth consistent with early members of the Homo genus, while a third specimen aligned more closely with Australopithecus, an older and more primitive group. The findings support earlier proposals that these fossils could represent two species, now referred to as Homo caucasi and Homo georgicus.
To evaluate whether these differences could simply reflect male and female traits within one species, the team compared the tooth size range to that of gorillas and chimpanzees, which show high levels of sexual dimorphism.
Although the Dmanisi specimens fell within the range observed in these apes, Nery explained that the distinct placement of one individual in comparison to the others suggested deeper taxonomic differences, not just size variation.
Implications for human origins and the possibility of two species
This evidence challenges the idea that early humans left Africa as a single, unified species. Instead, the presence of two species at Dmanisi hints at a more complex evolutionary picture, where multiple human lineages may have dispersed and evolved in different directions. According to the study, this could mean that early human expansion involved more than one branch of the genus Homo, possibly evolving in various regions outside Africa.
By identifying separate species based on dental analysis, the study adds a new layer to the ongoing debate about human origins and raises questions about the routes and timing of early migrations.
The researchers conclude that the fossil diversity at Dmanisi cannot be fully explained by size differences alone and is better understood as evidence of two distinct species sharing the same time and place.
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