Ancient human fossils reveal diversity in early populations

Chuck Bednar for – @BednarChuck

Two different fossils discovered just meters away from one-another suggest that early modern humans had a significant level of physical diversity, according to new research published online earlier this week in the open-access, peer-reviewed journal PLOS One.

By comparing a skull discovered at a cave in Laos in 2009 with a mandible located nearby in 2010, University of Illinois anthropology professor Dr. Laura Shackelford and her colleagues found that there was likely “a large range of morphological variation” in early modern humans.

Fossils from an important site in human migration

Both of the fossils were recovered from a cave called Tam Pa Ling in the Annamite Mountains, and the cranium is the oldest modern human fossil ever discovered in Southeast Asia. It’s discovery pushed back the date of modern human migration to the region by up to 20,000 years, revealing that humans migrated there from Africa far earlier than previously thought.

“The Tam Pa Ling site and fossils have significance for understanding the earliest migrations of modern humans into eastern Asia,” Dr. Shackelford told redOrbit via email. “This region is an important crossroads for early people who were migrating either to East Asia or to Australasia, and until recently the area has been completely unexplored.”

In her email, Dr. Shackelford added that the bones found at the Laos mountain cave site were “the oldest fossils from mainland Southeast Asia – and, in fact, outside of Africa or the Levantine corridor – that have secure dates and are definitively modern in their appearance. They show a great deal of interesting diversity that tell us a lot about these early humans.”

Same era, same location, but vastly different features

The jaw is roughly the same age as the skull, Dr. Shackelford’s team said, but unlike the cranium it was found to possess traits of both modern and archaic humans. For instance, it has a chin and other discrete traits consistent with early modern humans, the authors wrote, but retains a robust lateral corpus and internal corporal morphology typical of archaic Old World humans.

The mandible is “incredibly small in overall size,” the professor explained, and the presence of its protruding chin is more in line with typical modern human anatomy. On the other hand, the thick bone that the jaw has to hold molars in place are “more common of our archaic ancestors.”

“Mosaic morphology” not all that uncommon

Dr. Shackelford, who co-led the study with anthropologist Fabrice Demeter of the National Museum of Natural History in Paris, explained that this combination of archaic and modern human traits is not all that unusual. Fossils recovered from Africa, Eastern Europe and China also demonstrate the same type of what the authors call “mosaic morphology” as the mandible.

“Some researchers have used these features as evidence that modern humans migrating into new regions must have interbred with the archaic populations already present in those regions,” the study author explained in a statement. “But a more productive way to look at this variation is to see it as we see people today – showing many traits along a continuum.”


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