Near the northernmost tip of the Philippines is a deep, seven-chambered limestone cavern known as Callao Cave. In 2007, archaeologists digging in its chambers found a small finger bone — which, at 67,000 years old, was deemed the earliest evidence of a human presence in the archipelago. But for years, nobody was sure what kind of human it belonged to. Now, new bones and teeth found within the cave reveal an unexpected result: All of the artifacts belong to a new species of human known as Homo luzonensis.
As the archeologists describe in a remarkable new Nature paper, H. luzonensis, named for the island of Luzon on which they were found, is an undiscovered species of human. In the paper, the team report the discovery of 12 additional remains in the same strata of soil as the original finding, which they say are representative of at least three individuals. Co-author Eusebio Dizon, Ph.D., of the National Museum of the Philippines, tells Inverse that the team was already thrilled to have found more animal bones in the same strata as the 2007 discovery, but they didn’t realize until after that they’d stumbled on an animal of the Homo variety — one no one had seen before.
“The discovery was exciting, as there were animal bones as we identified them at that time at the breccia layer of more than 3 meters depth from the present surface; but [we didn’t] know yet if they were hominins,” he says in an email. “It was only when they were examined closely by Phil Piper and Florent Detroit when the real excitement was really felt.”
The team, which included Piper, Détroit, along with the finder of the 2007 finger bone, Armand Salvador Mijares, Ph.D., of the University of the Philippines, and others, report that they found seven teeth, two finger bones, two foot bones, and one femoral shaft in the same layer. Upon closer inspection of their weird characteristics, they realized they had never seen Homo features of this kind.
The teeth were a giveaway. The premolar to molar crown size ratio, they write, was high compared to other Homo species. The upper premolars have a shape that’s distinct from that of modern humans, Neanderthals, and Asian Homo erectus. The upper molars, meanwhile, were smaller than they’d seen elsewhere.
The other bones — the long and narrow manual phalanx, the third metatarsal, the proximal pedal phalanx, and so on — all showed similarities to a number of other Homo species, including the Neanderthals, Homo erectus, Homo floresiensis (the “hobbit”), Homo/Paranthropus, Homo naledi, modern humans, and even Australopithecus — apes that may have been the ancestors of the Homo genus. It was a strange combination of characteristics they hadn’t seen before. The new bones and teeth, and the original finger bone from 2007, were just different enough that they qualified as a new species — a particularly small one.
A Nature video published with the article notes that the bones and teeth of H. luzonensis suggest it was quite small, which is perhaps an effect of limited resources on the island giving an advantage to smaller-bodied individuals.
An accompanying article also published in Nature on Wednesday by Lakehead University anthropologist Matthew W. Tocheri, Ph.D., remarks that the discovery of H. luzonensis will “no doubt ignite plenty of scientific debate over the coming weeks, months, and years.” That’s largely because scientists have yet to conclude how humans traveled out of Africa, into Eurasia, and into even farther places only reachable by sea, such as the Philippine Islands.
“The origin of H. luzonensis, as well as its phylogenetic relationships with other hominins present in eastern Asia at around the same time — including H. sapiens, H. floresiensis and Denisovans, and hominins recently discovered in China — remains to be determined,” the team writes. They suspect the new species came to be unique because it was so isolated; the closest mainland regions are what we now know as China and Vietnam today.
The effects of “insular evolution,” they write, “may explain the distinct anatomy of H. luzonensis; however, further discoveries and more definitive evidence are needed.”
If this is really a new Homo species, then scientists will no doubt seek explanations about where it came from and from whom it descended. Did they descend from Homo erectus, and whose presence had already been established on the island of Java in the time before H. luzonensis? If not, was there some other early Homo species that made it to Asia that gave rise to this sea-faring people? And did they give rise to the “hobbit” H. floresiensis, the species identified on the island of Flores in Indonesia?
To answer these questions, scientists will have to return to the depths of Callao Cave, which may not be so easy given that it’s usually bustling with Homo sapiens. With its cathedral-like entrance lit by a stream of light from above, it’s a hotspot for human visitors — just as it might have been 67,000 years ago.
A hominin third metatarsal discovered in 2007 in Callao Cave (Northern Luzon, the Philippines) and dated to 67 thousand years ago provided the earliest direct evidence of a human presence in the Philippines. Analysis of this foot bone suggested that it belonged to the genus Homo, but to which species was unclear. Here we report the discovery of twelve additional hominin elements that represent at least three individuals that were found in the same stratigraphic layer of Callao Cave as the previously discovered metatarsal. These specimens display a combination of primitive and derived morphological features that is different from the combination of features found in other species in the genus Homo (including Homo floresiensis and Homo sapiens) and warrants their attribution to a new species, which we name Homo luzonensis. The presence of another and previously unknown hominin species east of the Wallace Line during the Late Pleistocene epoch underscores the importance of island Southeast Asia in the evolution of the genus Homo.