Path to discovery

An international research team first suspected they’d stumbled upon a historic new hominid back in 2007. Then, archeologist Armand Mijares of the University of the Philippines discovered a strange-looking third metatarsal human foot bone in Callao Cave that dated back 67,000 years.

Initially, the team took the fossil as further evidence of their team’s premise that ancient man was able to travel by ocean during the early stages of species development. Although they couldn’t quite place it with similar hominid species of the late Pleistocene era, such as Neanderthals (Homo neanderthalensis) or Homo sapiens (i.e. us), their hypothesis was solid.

To their surprise, subsequent Callao Cave excavations in 2011 and 2015 yielded an assortment of heavily-worn adult teeth from one or two individuals. They also discovered a foot bone, two finger bones, two toe bones and a shaft from a juvenile thigh bone, which increased their curiosity about the lineage of these ancient mariners in particular.

Because it wasn’t possible to extract DNA from this hodgepodge, their exam was limited to the traditional archeological tools, including micro CT scans and 3-D morphometric modeling.

Homo luzonensis' metatarsals' on display.
University of the Philippines (UP) Associate Professor Armand Salvador Mijares arranges fossils and teeth of a discovered new human species, the Homo luzonensis, at a press conference at the UP College of Science Auditorium in Manila on April 11, 2019. (Photo by Noel Celis/AFP/Getty Images).

No bones about it

The results? From the collected remains of two ancient adults and one juvenile, the team was able to determine that while these early beings bore resemblance to homo sapiens (‘wise man’) and Asian homo erectus (upright man), analysis of the two premolars and three molar teeth, linked to the same individual, indicated otherwise.

Regarding the teeth, the premolars and molars both were too small to fit Homo sapiens, and they still had two or three roots instead of one or two typical of our species. What’s more, the tooth dentin and the enamel that covers it resembled the tooth structure of more ancient hominids, such as Homo habilis (‘handy man’) and Homo erectus.

As for the foot findings, analysis of the third metatarsal fossil suggests that the ancients in question may have shared a distinctive walk, given that the proximal phalanx at the base of the toe is curved. This further suggests a possible primate-like gait and climbing ability. The team points out that the skeletal form is not found in Homo sapiens, but rather in the ancient Australopithecus, an exclusively African species that date back two to three million years.

Based on their foot and mouth findings, the researchers concluded that the fossils they studied did not fit any known homo genus, and named the world’s newest species Homo luzonensis on April 10. What’s more, the team suspects that the new species may have been the only one present at the time on Luzon, the largest island in the Philippines but one not accessible via a land bridge.

As for Southeast Asia, it’s been home to a number of hominins, including the similarly-pintsized Homo floresiensis, aka “the Hobbits,” named after the island of Flores in Indonesia where their remains were found.

With any new species announcement, colleagues sometimes turn a skeptical ear to the findings until the benefits of our biological heritage can be discussed, debated and ultimately absorbed. In the human puzzle, a dozen or more species of the genus Homo have been identified by scientists who share two distinctions: a passion for anthropology and membership in the only surviving Homo genus: Homo sapiens.

Is Homo luzonensis a ‘new’ species?

University of Washington anthropology researcher Elen Feuerriegel says the Luzon evidence, while compelling, may fall short of a distinct new species.

“I believe some caution is warranted before accepting this species diagnosis,” said Feuerriegel. “There is very little skeletal material to go on, so it is difficult to say with any certainty that these finds represent a new branch on the human family tree. I think to justify the recognition of a new species, we need more fossils and a more complete picture of what the Luzon population looked like.”

That being said, she’s intrigued by the new fossil data and what it suggests about our ancestral evolution in Southeast Asia.

“To me, the main anthropological significance for these findings is that they provide valuable information about the human fossil record in a part of the world that historically hasn’t had much to go on. The fossil record has been incomplete for this region,” Feuerriegel added. “We know based on finds of stone tools and other archaeological traces that archaic human relatives had been in Southeast Asia for around a million years (including on Luzon for 700,000 years), but the skeletal remains that go with those archaeological traces have been few and far between. The Luzon finds have contributed to that record significantly.”

Homo luzonensis found in Philippines.
University of the Philippines (UP) Associate Professor Armand Salvador Mijares shows a bone of a discovered new human species, the Homo luzonensis, at a press conference at the UP College of Science Auditorium in Manila on April 11, 2019. (Photo by Noel Celis/AFP/Getty Images).

University of Southern California anthropologist Dr. Craig Stanford doesn’t object to the species designation for Homo luzonensis. In fact, like the similar discovery of the Hobbit species in 2004, Stanford says the Luzon addition marks a healthy sign of the times in our search for our past.

“I think the main thing about it is, it’s discovery itself, because every time we think we have the family tree for humans complete, we learn just how naïve we really were,” said Stanford. “About 15 years ago, there was the discovery called the Hobbit because it’s kind of a tiny species that we still are arguing about exactly how to interpret, and at the time, that was completely unexpected and people didn’t want to accept it at first. What it really means to me is, the human family is far more diverse than we appreciate right now, and that realization is just going to increase in the coming years.”

In Stanford’s view, those who object to the new hominid as an island anomaly are missing the boat, just as our Luzon ancestors may have done by remaining island-bound.

“The evolutionary progression used to be seen as a ladder, and of course that’s totally not true; it’s more of a very intricately branching bush and that bush has many, many little twigs on it that emerged and existed for a time and then died,” Stanford added. “And this species is probably one of those tiny branches, as is the one we call the Hobbit. There are lots and lots of branches and in the end, they all ended up dying out except for the one that led to us. That’s what almost every other animal group on the planet is like; there are these evolutionary experiments that are taken. Our job is to figure out the complexity of it, which is why every few years we have a new species.”

“Like every other early human, we are a mosaic,” he concluded. “Today, we walk upright, of course; that’s a holdover from our earliest bipedal ancestors 5-6 million years ago. We have a grasping hand; that’s a holdover from our earliest primate ancestors 55 million years ago. We have a big brain; that’s a holdover from our most recent ancestors a few hundred thousand years ago. We’re just a mosaic of all the different stages of evolution that played a role in our history. We’re a product of our various ancestors.”