The landmark discovery announced in Nature on Wednesday, April 10, 2019 makes Luzon the third Southeast Asian island in the last 15 years to bear signs of ancient human activity. Homo luzonensis, a newly discovered human specie unknown to science, was found in Callao Cave in Peñablanca, Cagayan in northern Philippines. The specie is named after Luzon, the biggest island in the Philippines. It’s possible that Homo luzonensis stood less than three feet tall. The discovery adds growing complexity to the story of human evolution. The more fossils we find, the more we learn that many kinds of humans have lived on Earth.
The small-bodied hominin lived on the island of Luzon at least 50,000 to 67,000 years ago, during the Late Pleistocene epoch. The hominin – identified from a total of seven teeth and six small bones – hosts a patchwork of ancient and more advanced features.
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.
When Armand Mijares, a graduate student at the University of the Philippines 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. 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 co-author of the new study, who was looking through the animal remains. It was confirmed that it was human remains.
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. The team needed more fossils to be sure.
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 is unusually curved – a trait more commonly seen in more ancient cousins of modern humans, such as Africa’s australopithecines, a group that includes the famous human relative, Lucy, who trekked across Africa roughly three million years ago. The oldest fossil of hominins, dating back over six million years, have all been found in Africa. For million of years, hominins were short, small-brained, bipedal apes.
What is astounding about the discovery is that it is unlike any other previously known type of human and it is not known where their ancestors came from.
The common theory about human evolution is that Homo erectus originated in East Africa then spread eastward and were established in Southeast Asia by at least 1.6 million years ago. However, initial findings about Homo luzonensis does not point to Homo erectus as their ancestors.
Though other Homo species are known to have inhabited the Southeast Asian islands, the researchers think Homo luzonensis were the only hominins present on Luzon at the time. The earliest Homo sapiens known in the Philippines are fossils discovered in Tabon Cave on Palawan Island, dated to 30,000 to 40,000 years ago at the oldest. By contrast, archaelogists recently unearthed stone tools and bones from a butchered rhinoceros in a valley near Callao Cave, suggesting that Homo luzonensis or its ancestors were on Luzon as many as 700,000 years ago.
“Fifteen years ago, human evolution in Asia was very simple, with Homo erectus going out of Africa, settling in East and Southeast Asia and nothing happening until the arrival of Homo sapiens at around 40,000-50,000 years ago,” Florent Detroit, a paleoanthropologist at France’s Musee de l’Homme said. “This finding is a significant new piece of evidence to improve our knowledge of human evolution, especially in Asia, where human evolution was clearly much more complex (and much more interesting) than what we thought before.”