Homo Luzonensis

Humankind's tangled shrub of ancestry now has a new branch: Researchers in the Philippines announced today that they have discovered a species of ancient human previously unknown to science.

The small-bodied hominin, named Homo luzonensis, lived on the island of Luzon at least 50,000 to 67,000 years ago. The hominin—identified from a total of seven teeth and six small bones—hosts a patchwork of ancient and more advanced features. The landmark discovery, announced in Nature on Wednesday, makes Luzon the third Southeast Asian island in the last 15 years to bear signs of unexpectedly ancient human activity.

“For a long, long time, the Philippine islands [have] been more or less left [out]," says study coauthor and project leader Armand Mijares, an archaeologist at the University of the Philippines Diliman and a National Geographic grantee. But H. luzonensis flips the script, and it continues to challenge the outdated idea that the human line neatly progressed from less advanced to more advanced species.


Human Origins 101
“This new discovery made me thrilled,” Yousuke Kaifu, a paleoanthropologist at Tokyo's National Museum of Nature and Science who was not part of the new study, says via email. “It further highlights remarkable diversity of archaic (primitive) hominins once present in Asia, in a way beyond my expectation.”

Aida Gómez-Robles, a paleoanthropologist at University College London who reviewed the study before publication, is hesitant to unequivocally say the find represents a new species. But she adds that all possibilities to explain the unusual fossils are equally intriguing.

“It’s absolutely one of the most important findings that [will] be out in a number of years,” she says.


Digging deeper into Asia's past
Decades ago, the story of Asia seemed far more straightforward, if incomplete. Paleoanthropologists knew that archaic hominins such as Homo erectus ventured over land bridges into parts of what is now Indonesia nearly a million years ago. But farther east, it was thought that these hominins ran into ocean currents considered impassable without boats.

Luzon seemed especially difficult for ancient hominins to reach, as it had never been connected to the mainland by land bridges, so archaeologists thought that digging into deeper, older layers of soil wouldn't yield much. When Mijares first excavated Callao Cave in 2003, he found 25,000-year-old evidence of human activity—but he didn't dig any deeper than about four feet down.


“Most Southeast Asian archaeologists would only excavate cave sites up to two meters, and they would stop,” Mijares says.

That all changed in 2004, when researchers unveiled Homo floresiensis—a diminutive hominin, also known as the “hobbit,” that inhabited the Indonesian island of Flores until 50,000 years ago. Inspired, Mijares returned to Callao Cave in 2007 to literally dig deeper.


The team excavated more than five feet of clay below where they had stopped digging in 2003, with no fossils in sight. But then they found a layer of breccia, a type of rock formed from a jumble of other materials. Tantalizingly, this layer contained fragments of bone that had washed into the cave long ago. At first, the bones seemed to include only animals such as deer and pigs. But under closer inspection, one piece stood out: a nearly complete foot bone that looked human. The team sent the fossil to Philip Piper, a coauthor of the new study, who was looking through the animal remains.

“He called me up and said, Hello mate, you've got human remains,” Mijares says. “And I said, Really? Then we'll go grab a beer!”

In 2010, Mijares and his colleagues unveiled the 67,000-year-old fossil, which they tentatively suggested belonged to a small-bodied member of Homo sapiens, making it perhaps the oldest sign of our species anywhere in the Philippines at the time. But Mijares suspected that it might actually belong to a new species, maybe even a Luzon analog to H. floresiensis. The team needed more fossils to be sure.


Something old, something new
As luck would have it, excavations uncovered two more toe bones along with seven teeth, two finger bones, and part of a femur on return trips to Callao Cave in 2011 and 2015. In all, the remains represent at least three individuals.

The small fossils' curves and grooves reveal an unexpected mix of both ancient and more advanced traits. The teeth's small sizes and relatively simple shapes, for instance, point to a more “modern” individual, but one upper premolar has three roots—a trait found in fewer than 3 percent of modern humans. And one foot bone resembles those of the ancient australopithecines, a group that includes the famous human relative Lucy, who trekked across Africa roughly three million years ago.


Five of the seven teeth attributed to Homo luzonensis. The teeth have small sizes and relatively simple shapes, but one premolar has three roots, which is uncommon among modern humans.

“I agree with [the] authors that the combination of features is like nothing we have seen before,” says María Martinón-Torres, the director of Spain's National Research Center on Human Evolution.


New York University anthropologist Shara Bailey, an expert on ancient teeth, notes that South Africa's Homo naledi—discovered by a team including National Geographic grantee Lee Berger—also has features that look both ancient and modern. She takes the two discoveries as a sign that “mosaic” evolution was more common among hominins than once thought.

Martinón-Torres further suggests that the mix of dental features somewhat resembles that seen in 15,000-year-old hominin remains from Dushan in southern China, which she and her colleagues recently described. Along with H. luzonensis, the discoveries join recent finds hinting that by 12,000 years ago, as the Pleistocene epoch drew to a close, hominins in Asia had a startling amount of diversity.

What's in a name?
While many scientists laud the research for its thoroughness, defining a species from just 13 small bones and teeth is tricky. Though the scientists attempted to extract DNA, they were unsuccessful, as is common for samples that have stewed for millennia in the heat and humidity of tropical locales.