Scientists may have discovered a new human relative. It lived on a tiny island in the Philippines at the same time as Homo Sapiens.

• Anthropologists may have discovered a new human relative in the Philippines.
• Named Homo luzonensis after the island it was discovered on, this ancient hominin lived between 50,000 and 67,000 years ago.
• A new study discusses how H. luzonensis shares traits with both older human ancestors like Australopithecus and Homo erectus, and also modern-day humans.
• Not all anthropologists are convinced it is a new species, but the discovery indicates this time period in our evolutionary history was far more complicated that scientists thought.

In a hidden cave in the heart of the Philippine jungle, archaeologists have discovered a new human relative.

At the northern tip of the Philippines lies the tiny island of Luzon, and some 50,000 years ago, an ancient hominin species lived and thrived there, according to a study published April 10 in the journal Nature.

Hominins are any ancestors in the human lineage (including modern-day Homo sapiens) who are more closely related to each other than they are to chimpanzees. That includes everything from stone tool-wielding Homo erectus to our Neanderthal cousins.

Read More: Nibbled-on bones found in a cave revealed that our Neanderthal ancestors ate each other. Scientists may have figured out why.

Scientists already knew that hominins lived on Luzon, given the 2010 discovery of a single foot bone dated to 67,000 years ago in the Callao Cave on the northern end of the island. But they didn't know whether that foot bone belonged to a member of Homo sapiens or an individual that was part of a new species.

The new study describes the discovery of additional fossils - several other foot and hand bones, a partial thigh bone, and seven teeth - in Callao Cave, which helped anthropologists determine that a previously undiscovered ancient hominin once lived on Luzon tens of thousands of years ago.

The finding will help scientists "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," lead author of the study, Florent Detroit, told Business Insider.

Detroit and his colleagues named the species Homo luzonensis, after the name of the island. It's the first new hominin species discovery since Homo naledi was discovered in South Africa in 2015.

A mosaic of traits made this hominin species hard to categorize

The researchers assigned the bones that they found to three H. luzonensis individuals - two adults and one child.

"Overall these teeth and bones have a striking combination of characteristics never before reported together in a hominin species," Matthew Tocheri, an anthropologist from Lakehead University in Ontario who was not involved in the study, wrote in a follow-up article for Nature.

H. luzonensis' teeth, for example, have a hodge podge of traits that match the teeth of Homo sapiens, Homo erectus, and another smaller-brained human ancestor, Paranthropus, in different ways.

The new species' teeth are "astonishingly small," Tocheri said, with not a lot of complexity on the crown surfaces (those tiny grooves and crevasses on the tops of teeth) - suggesting that H. luzonensis' teeth were more like those of modern humans.

On the other hand, H. luzonensis' hands and feet retained more "primitive" features, like those found in our older ancestors like Australopithecus afarensis and Australopithecus africanus - despite the fact that this new species and Australopiths are separated by 2 to 3 million years of time and evolution.

The new species' hand and foot bones were curved, and according to Tocheri, its toe bones were "essentially indistinguishable" in shape from Australopith toes.

In the study, the authors pointed to the fact that the unique combination of H. luzonensis' Homo-like teeth and Australopith-like hands and feet hasn't been seen in any other specimens in the fossil record, which "warrants their attribution to a new species."

Is H. luzonensis actually a new species?

Jeremy DeSilva, an anthropologist from Dartmouth College who was not involved in the study, still isn't convinced that the individuals classified as H. luzonensis represent a new hominin species.

"Whenever there's a new discovery like this, it's like Christmas morning for me," DeSilva told Business Insider. "But I'm not sure that I'm willing to accept that this is a new species quite yet."

He added that he doesn't think the researchers have enough fossil material to make this claim. "I'd like to see more; I'm sure they would too," he said. "Maybe a skull, a knee, an ankle, or a heel - more than three footbones, when each individual has 52."

Another anthropologist who was not involved in the discovery, William Harcourt-Smith from Lehman College, agrees with DeSilva, and told Business Insider that he was "cautious" about the designation.

"Assigning this to a new species is right at the margin for what's acceptable," Harcourt-Smith said. He echoed DeSilva's desire for additional material before making a definitive case for a new species, saying that the current evidence is "too meager" to make a definitive case one way or another.

There just isn't enough evidence yet, according to some anthropologists

Two of the most recent hominin species discoveries were based on far more fossil material than Homo luzonensis' unveiling was.

When scientists discovered Homo floresiensis, nicknamed "the Hobbit" for its short stature, on the Indonesian island of Flores, they described a near-complete female skeleton, including a skull. Since the discovery in 2003, bones and teeth from some 12 H. floresiensis individuals have been recovered at the Liang Bua cave .

The discovery of Homo naledi included at least 15 individuals, which allowed the anthropologists to study and assess several specimens of the same bone.

But when it comes to Homo luzonensis, scientists have found just 13 bones total, and for DeSilva and Harcourt-Smith, that just isn't enough data to make the call on whether what Detroit and his colleagues found in the Phillippines is a new species.

"I'm going to consider myself a fence sitter on this one," DeSilva said about whether or not he agreed with the designation.

H. luzonensis probably lived undisturbed on the island for thousands of years

H. luzonensis' mosaic of traits makes it difficult to determine where it sits on the human family tree related to its other hominin brethren.

"Almost every aspect of the new fossils was (and are still) surprising," Detroit said. Almost all of them show unexpected features for a "recent" hominin that lived at the same time as Homo sapiens, he added.

All the anthropologists agreed that H. luzonensis' feet were of particular interest.

"The anatomy is eye brow-raising," DeSilva said. He said the new species' foot bones don't fit into the range of what scientists might find in modern humans - or other hominin species.

Typically, curved hands and feet like H. luzonensis' suggest that the species climbed trees at least some of the time. Australopiths with similar features likely walked on two feet while still being able to climb trees.

But the problem with this new species is that it lived at least 2 million years or so after Australopiths, during an era when anthropologists generally accept that all human ancestors only walked on two feet and did little else.

"We are certainly not pretending that H. luzonensis was "back to the trees," Detroit said. Instead, the study authors think the primitive, curved foot bones might have something to do with H. luzonensis' island habitat.

In order to get to Luzon from mainland Asia, H. luzonensis would have had to partake in a sea crossing. The surrounding water made accessing Luzon a challenge, limiting species migration onto and off the island.

Isolated habitats like islands are ripe for the appearance of unique sets of traits, which the study authors think could explain the species' distinct anatomy, including its "primitive" hands and feet.

What this species tells us about our human relatives' evolutionary history

According to Detroit, 15 years ago, scientists' conception of human evolution in Asia was very simple. Homo erectus migrated out of Africa to settle in east and southeast Asia around 1.8 million years ago, with "nothing happening until the arrival of H. sapiens" in the area until around 40,000 to 50,000 years ago, when modern humans eventually took the place of H. erectus.

That version of our evolutionary history no longer holds water.

Detroit's team dated H. luzonensis' age to somewhere between 50,000 and 67,000 years old. That means this hominin was alive at the same time as at least four other human relatives: Neanderthals, Denisovans, Homo floresiensis, and modern humans.

"We continue to realize that few thousands of years back in time, H. sapiens was definitely not alone on Earth," Detroit said. "The scenario was clearly much more complex than just H. sapiens replacing H. erectus."

There's no question that these fossil are something different, Harcourt-Smith said. "It's not modern human, doesn't seem to be a hobbit either, but we need more data. This is just a tantalizing glimpse of how diverse hominins really were."

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