An unknown species of hominin has been discovered in the Philippines, an international team of scientists reported in Nature on Wednesday. They lived on the island of Luzon and had such a strange mix of features — including rather monkey-like feet — that archaeologists admit to being baffled as to their origin.
Because of its unique mosaic of characteristics, scientists say the hominins warrant the definition of a new species: Homo luzonensis.
Moreover, they didn’t go extinct long ago. Fossilized teeth and bones from at least three individuals found in Callao Cave, on Luzon’s northern coast, were dated to just 50,000 and 67,000 years ago. They were definitely contemporary with Homo sapiens in the region (if not necessarily on Luzon).
Some of Homo luzonensis’ features were primitive like Australopithecus and some were modern like the more advanced Homo genus, the researchers report. But they can’t yet tell what it looked like. The remains discovered so far are so scanty that basic questions remain open — even whether this species walked on the ground like other Homo species.
Yet for all the paucity of fossil evidence, the researchers could determine that the new hominin’s set of primitive and modern features is unlike any other known species of Homo: Not Homo sapiens; not Neanderthals; not Denisovans; and not Homo floresiensis, a mysterious tiny hominin that lived on the Indonesian island of Flores within the same time frame.
It is intriguing that the Southeast Asian islands were, at roughly the same time, home to not one small hominin species tens of thousands of years ago, but two.
Homo floresiensis was just over a meter (3 feet) in height and lived about 2,800 kilometers (1,740 miles) away as the bird flies, which is just one reason to assume they had no contact or relationship with the hominins on Luzon. Homo floresiensis, dubbed the hobbit, survived until around 50,000 years ago, and seems to have originated in early hominins who reached Flores by a million years ago.
The earliest known hominin evidence out of Africa dates to 1.8 million years. But the fact is that stone tools have been found in China that are more than 2 million years old.
The paradigm that only Homo erectus left Africa for the wilds of Eurasia around two million years ago was already looking obsolete. Now we have this new species that may not have arisen from an erectus. There may well have been multiple exits from Africa, for which we have yet to find paleontological evidence.
Détroit doesn't support the notion of an exit as early as the Australopithecine, however. "It is theoretically possible, but I would say that it is not very probable taking into account our current knowledge on the prehistory and fossil record of Asia because there is absolutely nothing related to Australopithecus discovered outside of Africa so far," he tells Haaretz.
Once there was a rhino
Back on Luzon, the discovery of hominins from 67,000 years ago was not a shock. Previous research on the island found that 709,000 years ago, a rhinoceros had been butchered using stone tools that were found in association with the unfortunate animal. That happened at Kalinga in the north-center of the island, about a two-hour car ride inland from Callao.
Which archaic hominins ate the rhino remains unknown. No hominin fossils were found in the 709,000-year-old site, so we cannot know if they were H. luzonensis, its ancestor, or some other being.
In fact, H. luzonensis could have descended from a different group of hominins entirely that also settled on Luzon at some point in the past but whose remains have yet to be found, the researchers point out.
What was H. luzonensis like? The remains are too scanty to say much for sure, and they are confusing to boot. It and H. floresiensis both display present anatomical traits that are either rare or absent elsewhere in the genus Homo — but bear similarity with, of all people, Australopithecus.
Clearly, human evolution bears rethinking. The odd mélange of archaic and modern features H. luzonensis presents is further evidence that the timeline of human evolution is not linear, as had been supposed.
Both Africa and Asia had multiple species of contemporaneous hominins — meaning their timelines overlapped. At least sometimes, they interbred, and there were evidently a lot of exits from Africa by all sorts of species. When H. luzonensis lived, so did Neanderthals, Denisovans, hobbits, us, and probably others too.
“Until less than 20 years ago, human evolution in Asia was very simple, with H. erectus going out of Africa, settling in East and Southeast Asia and … nothing happened until the arrival of H. sapiens at around 40,000 to 50,000 years ago and its ‘conquest’ of every region on Earth,” says lead author Florent Détroit of the National Museum of Natural History in Paris. But it can’t have been so.
Regression to the trees?
Callao Cave is a beautiful limestone complex of caves in the Peñablanca Protected Landscape and Seascape national park. The first hominin discovery, found in 2007 and reported in 2010 by the co-author of this paper, Armand Mijares of the University of the Philippines, was of a long foot bone (a third metatarsal) that dated to 67,000 years ago. Subsequently, 12 more hominin elements were found in the same layer: seven upper jaw teeth; two finger bones; two toe bones; and a thigh bone from a juvenile.
These remains belonged to at least three individuals, the scientists deduce. Five of the teeth belonged to one individual. The other two teeth were both right upper third molars, so they had to belong to two more individuals.
DNA could not be extracted from the ancient bones, denying that avenue of enlightenment.
Again intriguingly, though proving little, the teeth were extremely small in the scale of the Homo genus.
Among primates, tooth size correlates to body size — but there are exceptions. “We have to stay cautious with body size estimation of Homo luzonensis because it is very difficult to tell from the elements we have,” Détroit explains.
H. luzonensis teeth were even smaller than the hobbit’s, but the foot bone was in the variation range of larger (yet still “pygmy”) H. sapiens such as the Philippine Negritos. So, based on the teeth and foot bone, the scientists sum up that H. luzonensis was probably small-bodied.
Also, while our premolars have one or sometimes two roots, H. luzonensis had two to three, which is similar to Australopithecus and ancient species of the genus Homo, such as Homo habilis and Homo erectus, Détroit says. But their molars looked more like ours. By the way, the teeth all but rule out that their ancestors were Denisovans, because they had huge teeth.
Yet the most astonishing aspect of their discovery, the scientists share, is the primitive Australopithecus-like aspects of the foot, utterly different from Homo sapiens’, in a species that lived so recently.
In Australopithecus, which lived in Africa 4 to 2 million years ago, the foot structure is generally interpreted as evidence that they were bipedal but also spent time in trees. (A baby Australopithecus’ foot was chimp-like, leading to the theory, published in 2018, that young australopithecines kept to the trees for safety.)
They are not suggesting that H. luzonensis reverted to an arboreal lifestyle, Détroit stresses: Its feet may have regressed during their island isolation.
H. luzonensis’ proximal phalanx — the closest to the foot of the two bones in each toe — displays very marked curvature and very developed insertions for the muscles involved in flexing the foot, Détroit explains. “These characteristics do not exist in Homo sapiens. In contrast, this phalanx strongly resembles those of Australopithecus, known only in Africa and at much older periods.”
Which begs the question of why they would regress and return to the trees, if they did. It’s all speculation, but we know Luzon in the Middle Pleistocene had rhinoceroses: it may have had more dangerous animals. We are certain there were rats, for what that’s worth. Large hairy-tailed rats. They are prettier than their name might suggest.
Archaic hominins on the briny?
Taking H. Luzonensis’ features one by one, each can be found in one or several hominin species, Détroit says: But the entirety of their features is unique (especially the teeth) and warrant classification of a new species.
Not that he thinks this accomplishment, of defining a new species, is necessarily a big deal. Mainly they’re happy less because of “glory or absolute ‘scientific value,’” and more because the news attracts interest and fuels debate among peers and the public at large, he says.
“If in the future colleagues are able to show that we were wrong because the fossils can enter one of the already known hominin species, we will just lump it and forget about it. But in the meantime, I am convinced it is the way we had to do it to improve our knowledge and understanding of the evolutionary history of hominins,” Détroit says.
H. luzonensis isn’t the only hominin with a mix of primitive and modern characteristics that have researchers at each other’s throats: H. Naledi, discovered in South Africa in 2013, was another. Living a quarter-million years ago, its brain was about 40 to 45 percent the size of ours, like an Australopithecine, but speculation arose that it buried its dead. The jury is out on what a collection of Naledi bodies was actually doing in an extremely deep, inaccessible part of a cave system.
Another question that must remain unanswered for the nonce, and probably forever, is how archaic hominins reached islands in the first place hundreds of thousands of years ago. The Philippine islands have been isolated from mainland Southeast Asia for 2.6 million years. (Crete has been isolated for 5 million years, yet stone tools were found from at least 130,000 years ago — much later than the arrival on the Southeast Asian islands but still curious.)
It seems that Homo Erectus and/or Homo heidelbergensis could cross water.
But how? Accidentally drifting on some raft of vegetation or pumice? Or could they sail? The argument rages on, bereft of evidence other than their sheer presence. Détroit, for one, belongs to the school suspecting that they went to sea, though they wouldn’t necessarily have had a sense of knowing where they wanted to go.
“We can imagine hominins practicing something very different from what we now call ‘navigation’ i.e. just going on the sea for short distance trips,” he says, arriving without plan on a very distant island.
Note that you can’t establish a settlement on an island and develop a viable population with a single event of arrival of only few people, Détroit adds. “You need several individuals, of course, and you need several arrivals, at least at the beginning, so you have enough founders settled on the island.”
And then, Homo sapiens arrived. The earliest evidence of anatomically modern humans in the Philippines was found in Tabon Cave on Palawan island, and dates to 30,000 to 40,000 years ago — some 10,000 years after the latest H. luzonensis fossil. Which doesn’t mean the two species didn’t meet on Luzon, but we have no evidence they did.
It is pointless to speculate about whether Homo sapiens killed off the “rival” species, from the hobbit to the apparently outsized Denisovan. We simply don’t know and have no evidence other than our sunny natures.