Homo luzonensis: A small, ancient human species from the Philippines

The story of human evolution is not straightforward. It’s a tale that’s full of overlapping narratives and missing pages that’s constantly being revised.

One of the most enigmatic species in this evolutionary tale is Homo luzonensis, whose remains were discovered on the island of Luzon in the Philippines. Just 13 fossils of this ancient human species have been found so far. They come from at least two adults and one juvenile.

With so few fossils to study, it’s hard to say what these early humans looked like or how they lived. The size of the fossils suggests they were short, but many other details remain a mystery. As a result, the status of this hominin is uncertain. Research is ongoing to try and better classify Homo luzonensis and find out if it’s even a species at all.

Professor Chris Stringer, one of our human evolution experts, says, “some scientists have questioned the wisdom of creating a new species, given the small sample of fossils”.

“Others, including myself, wonder whether the Luzon finds might be related to the already known Homo floresiensis. We know that island isolation can be a catalyst for some odd evolutionary changes, including reversions to apparently primitive states.”

“Nevertheless, for the moment it’s probably reasonable to accept Homo luzonensis as a species while we await more finds.”

Southeast Asia: A human evolution hotspot

While human evolution was once thought to be a straightforward family tree, it now turns out to be more of a bush.

More and more ancient human species are now known to have lived alongside each other within the past 150,000 years. This suggests that there may have been significant overlap between our own ancestors and these ancient species.

Southeast Asia, in particular, was once home to numerous species of human. In an early migration out of Africa, the incredibly successful Homo erectus made it to China and Indonesia by about 1.5 million years ago.

The enigmatic Denisovans, a relative of the Neanderthals, may even have reached the area near Papua New Guinea. They later bred with the ancestors of people who live in the region today.

It’s thought these dispersals took place by land. Until recently, the seafaring ability of early humans was often dismissed. However, the discovery of Homo floresiensis on the island of Flores in the Indonesian archipelago changed all this.

When H. floresiensis was found, it sent shockwaves through the field of anthropology. There was a deep channel of water isolating the island of Flores when these small humans were alive, meaning their ancestors can only have reached it via a sea crossing.

Likewise, the island of Luzon has never been attached to the Asian mainland. So, H. luzonensis’ ancestors must have crossed the ocean to get there, further supporting theories that ancient humans were using rafts to explore.

When was Homo luzonensis discovered?

The site where H. luzonensis was found, called Callao Cave, was first explored in 2003. After excavating a few metres of sediment, the researchers found nothing of note and so abandoned the site. With no reason to assume that ancient humans had once made it over to Luzon, there was no reason to explore further.

That was until H. floresiensis hit the headlines. Suddenly, it was clear that ancient humans could reach these seemingly inaccessible islands, so the researchers went back to Callao Cave in 2007 to dig a little deeper.

Among a layer of animal bones, they made the discovery of a nearly complete human foot bone. Further excavations revealed more human material, convincing researchers they’d found a new species of ancient human.

Homo luzonensis description

In total, scientists have so far found 13 H. luzonensis fossils, including adult finger and toe bones as well as teeth. They also found an upper leg bone – femur – from a child. The features of the remains show an intriguing mix of both modern and ancient aspects.

For example, while the teeth look more like those of modern humans, the hands and feet seem to match more closely with australopithecines. These distant human relatives lived between about two and four million years ago in Africa and their skeletons suggest they spent at least some of their time in trees.

H. luzonensis has similar curves in the toe and finger bones to those of australopithecines. This suggests that it might have climbed trees too.

The lack of other fossils, especially a skull, means that many other characteristics, such as its brain size, remain unknown.

Homo luzonensis body size

The body size of H. luzonensis is difficult to estimate because of the small number of known fossils from the species. However, Professor Philip Piper – one of the team who named the species in a paper published in Nature – explains there are some clues.

“Homo luzonensis has some really interesting features,” Philip says. “For example, the teeth are really small.”

“The size of the teeth generally – though not always – reflect the overall body size of a mammal, so we think Homo luzonensis was probably relatively small too.”

“Exactly how small we don’t know yet. We would need to find some skeletal elements from which we could measure body size more precisely.”

How old is Homo luzonensis?

At the time of its discovery, Homo luzonensis was estimated to be around 67,000 years old. However, more recent research suggests they’re actually much older.

Chris and his colleague Professor Rainer Grün re-examined a variety of important human fossils in 2023 using a technique known as uranium series dating.

Their investigations revealed that the remains of H. luzonensis might have absorbed uranium after burial, making them appear younger than they are.

“Our analysis suggests that these fossils are even older than the 67,000-year age originally given to them,” Chris explains. “Instead, we found that Homo luzonensis could be at least 130,000 years old.”

Homo floresiensis and Homo luzonensis

Due to its short stature, H. luzonensis has been compared to H. floresiensis – another short, ancient human species – ever since its discovery.

While H. floresiensis was found thousands of kilometres from Luzon, the presence of two miniature humans with primitive features in southeast Asia raises intriguing questions. One possibility is that they’re both actually the same species or at least very closely related.

Alternatively, they might be separate species that evolved independently but both succumbed to island miniaturisation – where a lack of resources and competition on islands causes larger-bodied animals to shrink.

“Some will argue that the primitive features of H. luzonensis are evidence of a pre-Homo erectus dispersal out of Africa, perhaps more than two million years ago,” says Chris.

“H. floresiensis and H. luzonensis would represent some of the last survivors of that primitive early wave, lingering on at the fringes of the inhabited world. If this explanation turns out to be correct, it would even question whether these species really belong in the genus Homo.”

“Others would prefer to regard these island forms as descendants of Homo erectus, subject to isolation and island miniaturising over a considerable period of time.”

Homo luzonensis ancestors

While the current lack of DNA and fossil evidence makes it difficult to know who the ancestors of H. luzonensis were, there are signs of even earlier humans on Luzon.

A collection of stone tools and animal remains have been found around 50 kilometres from Callao Cave at a site known as Kalinga. Many of the animal bones, including the skeleton of an ancient rhino, show signs of being butchered.

While there aren’t any human remains to show what species might have been eating these animals, the site has been dated to around 700,000 years ago.

When did Homo luzonensis go extinct?

So far, the only fossils of this species that have been found are the ones in Callao Cave. As they’ve all been dated to the same time, it’s currently unknown when Homo luzonensis’ extinction was.

Fossil evidence of our species, Homo sapiens, first appears in the Philippines between 40,000–50,000 years ago, while genetic evidence suggests that they might have arrived at least 55,000 years ago.

Many other ancient human species, such as the Neanderthals and H. floresiensis, went extinct around the same time H. sapiens was spreading around the world. It’s possible that this is also true of H. luzonensis, but at the moment there’s just not enough evidence to prove this one way or the other.

Only with the discovery of more ancient human remains on both Luzon and other southeast Asian islands will we begin to discover the answers to questions such as these.