Virtual reconstructions of the Xuchang 1 and 2 skulls, superimposed on the archeological site near Xuchang where they were discovered. Image Credit: Xiu-jie Wu

Hundreds of thousands of years ago, a variety of scruffy hominins roamed the planet, making tools, chasing down dinner, sitting around fires, and looking at the stars. Unfortunately, they didn’t leave much behind. Figuring out how and when these populations spread across the globe and intermingled with each other is a huge puzzle, one with most of the pieces missing.

That’s why scientists are excited about the discovery of two archaic human skulls in China reported in the journal Science today, March 2. These 100,000-year-old fossils have a mix of traits—and even some similarities with Neanderthals—which bolsters the idea that the precursors to modern humans were a diverse bunch who routinely interbred with one another.

Mental_floss spoke to report authors Erik Trinkaus, a professor of anthropology at Washington University in St. Louis, and paleoanthropologist Xiu-Jie Wu, of the Chinese Academy of Sciences in Beijing, as well as several experts in human evolution who were not involved in the current research.

The two broken skulls were discovered in the outskirts of Xuchang in central China at the Lingjing site, which was a spring for most of its history. The water consistently attracted people and animals over many millennia, and scientists have found at the site thousands bones of creatures like extinct deer and rhino relatives, as well as much more recent Bronze Age remains.

When the water table was lowered in the area in 2007, Lingjing became drier, and scientists were able to start an excavation, says Trinkaus. While digging, the researchers found the two skulls of archaic humans. They died in the Late Pleistocene, about 100,000 years ago.

“These were hunters and gatherers who, if you saw them, would look basically like people today,” Trinkaus says. “We would probably find them rather dirty and uncouth, but they were basically people.”

The skulls show that these almost-people have some similarities with early modern humans, including a large brain size and modest brow ridges. But they also have some important physical differences. Their low and broad braincase is characteristic of earlier, more primitive eastern Eurasian humans. Meanwhile, the shape of the semicircular canals (bones near the inner ear) and arrangement of the back of the skulls are similar to contemporary Neanderthals from western Eurasia.

This mosaic of physical features “suggests a pattern of regional population continuity in eastern Eurasia, combined with shared long-term trends in human biology and population connections across Eurasia,” says Wu. Those long-term trends include increasing brain size and decreasing massiveness of the skull—patterns that are also seen in humans in western Eurasia and Africa during this time period, which suggests some trends could be universal among humans, Trinkaus says.

The human-evolution experts we spoke to gave a number of reasons why the find is significant.

“It is a fascinating new discovery,” says Lynne Schepartz, a paleoanthropologist at the University of the Witwatersrand in South Africa. “The presence of the Neanderthal traits is very clear and, in my opinion, unquestionable. This discovery demonstrates the diversity of eastern Asian populations in the Late Pleistocene, reflecting their roots in earlier Homo erectus populations and then increased gene flow and interaction with peoples from the West.”

Fred Smith, an anthropologist at Illinois State University, says the skulls add to two growing points of consensus in paleoanthropology: “Neanderthals had extensive evolutionary influences beyond their core area of western Eurasia, and archaic human groups routinely hybridized with each other, and with early modern humans.”

In fact, this study highlights how the once-common image of Neanderthals as an anomalous European population, distinguished by a set of regional peculiarities, is now “looking increasingly dubious,” according to Boston University anthropologist Matt Cartmill. Instead, he says, recent research suggests that some of the traits we think of as unique to Neanderthals could have been widely distributed in late archaic human populations all across Eurasia. “I am beginning to wonder how useful the concept ‘Neanderthal’ is."

Other researchers say the skulls' combination of primitive features and Neanderthal-like traits should be somewhat expected in archaic humans in East Asia from this time period. “This is exactly what the Denisovans (an Asian sister group of the Western Eurasian Neanderthals) should be,” says Jean-Jacques Hublin, director of the department of Human Evolution at the Max Planck Institute for Evolutionary Anthropology in Germany.

The authors of the paper, however, have shied away from assigning a species name or category to these archaic humans just yet. Trinkaus says there isn’t enough known about the Denisovans and that using such a category would not be helpful for understanding the messy population dynamics of archaic humans.

“It’s not the kind of thing that you can make a simple diagram of with lines on a piece of paper,” he explains. “It’s a very complex process.”

But Trinkaus is hopeful that further research at Lingjing, along with discoveries elsewhere in China and East Asia, will shed more light on what these ancestral humans were like. “In the last couple of decades there’s been a renaissance of Pleistocene archaeology and paleontology in that part of the world,” he says.