Since 2007 a group of archaeologists have been probing through Callao Cave on the Philippine island of Luzon. And throughout the course of their investigations, these researchers have uncovered some rather curious fossils. But in April 2019 the truth about these finds finally came out – raising big questions about mankind’s evolution.
Callao Cave is actually a limestone landform found in the northern Philippine province of Cagayan on Luzon island. Located in the Sierra Madre mountain range, it is also one of Cagayan province’s biggest draws for tourists. Yet Callao is just a single cave out of some 300 others sprinkled throughout the region.
At one time, though, Callao Cave consisted of nine chambers. But an earthquake during the 1980s blocked two, leaving only the other seven accessible and enjoying natural illumination. Yes, gaps in the rocks allow light to travel underground and brighten up each chamber.
The biggest chamber in Callao Cave is around 160 feet wide and 118 feet high. And possibly because of the chamber’s grand scale, locals in the area saw fit to turn it into a chapel. Amazingly, too, this house of God – lit by that natural light traveling through slits in the ceiling – even has an altar of rock.
Yet environmental processes within the Callao Cave complex have promoted the formation of several other fascinating features within each of the chambers. Specific examples of these include cave curtains, flowstones and dripstones. And particularly within the more deep-seated chambers of the network, formations known as stalagmites and stalactites have also developed.
Both stalagmites and stalactites form from a build-up of minerals deriving from drops of water. A stalagmite specifically points upward from the ground, and its end tends to be relatively flat. A stalactite, on the other hand, points down from the top of the cave and tends to have a sharper end.
Of the many caves found throughout Cagayan province, then, Callao is known to draw the most visitors. Yet in addition to the fascinating features that Callao boasts, its attraction is also likely down in part to it being relatively easy to access. In fact, one can enter the cave simply by traipsing up a series of manmade steps.
Yet even though the cave is open to the average sightseer, Callao is also subject to interest from archaeologists. In particular, a Filipino researcher called Armand Salvador Mijares has spent his fair share of time exploring the complex. And the fruits of his labor may well prove significant to our understanding of the human species.
Back at the beginning of the 2000s, you see, Mijares was a student at the University of the Philippines. And around this time, he decided to start investigating Callao Cave in search of evidence of ancient farmers. But after a while, the focus of his research morphed into a pursuit for something else entirely.
That’s because in 2004 archaeologists in Indonesia uncovered evidence of a species, supposedly related to modern humans, called Homo floresiensis. So Mijares began to wonder if this species may also have managed to make its way to the Philippines. As he put it in a 2019 interview reported by The New York Times, “That inspired me to go back [to Callao] and go deep.”
So in 2007 Mijares and a team of archaeologists did just that. They in fact traveled to Callao Cave and started to excavate – eventually coming across bones. Initially, however, there didn’t appear to be anything particularly exciting about these new finds. In fact, it seemed that the bulk of the bones derived from deer and other known mammal species.
But then a specialist from the University of the Philippines called Philip Piper noted something different. After studying the discoveries, in fact, the researcher discerned a bone that appeared to be from a human foot. But it was relatively small, and, as Mijares put it, “there was something weird about it.”
Yet the researchers were unable to reach any solid conclusions based on the discovery of just one bone. So they continued to search through the network of caves. And over the course of the next few years, the archaeologists found teeth, parts of hands and a piece of a thigh bone.
The teeth were especially notable because they had some unusual characteristics. For instance, the teeth of modern humans tend to have merely a single root. But some of the newly discovered teeth actually possessed three roots. And on top of that, the teeth themselves could be considered to be extremely small.
Debbie Argue, a paleoanthropologist from the Australian National University, has expressed the potential significance of these finds. “These adult teeth are smaller than any hominin [the taxonomic tribe to which humans belong] known,” she said in April 2019, according to The New York Times. “Could it be that these teeth belonged to adults that were even smaller than Homo floresiensis?”
So the small teeth are apparently potentially indicative of a type of human smaller than four foot in height. Elsewhere, it was also noted that an uncovered toe bone is actually arched. And this is of a similar nature to that of a different species known as Australopithecus, which had only previously been found in Africa.
Owing to these apparently unusual traits, then, it’s been proposed that the bones actually belonged to an unknown kind of Homo. In fact, this is precisely the verdict of Mijares and several other experts. But given that only a small sample had been discovered at that time, it was far from a foregone conclusion.
On April 10, 2019, though, Mijares and his colleagues published a paper in the scientific journal Nature. And here they claimed that their investigations over the years had, in fact, uncovered a previously unknown species. They christened this species Homo luzonensis after the island where the bones had been found.
According to the study, then, examinations of some of the fossils suggested that they were at least between 50,000 and 67,000 years old. That means that the discoveries could draw yet more archaeological attention towards the Philippines. “This puts the Philippines – our scientific community – in the spotlight,” Mijares stated, according to Time. “Before, we [were] just peripheral in this debate of human evolution.”
Homo luzonensis’ discovery could ultimately prove to be significant within the context of our understanding of human evolution too. After all, it was once generally believed that modern humans derived from a relatively simple line of ancestors. But as the years have passed, and new evidence has been uncovered, this has increasingly appeared not to be the case.
Matthew Tocheri, a paleoanthropologist from Canada’s Lakehead University, phrased it succinctly to The New York Times. He said, “The more fossils that people pull out of the ground, the more we realize that the variation that was present in the past far exceeds what we see in us today.”
At the moment, then, humans are thought to be able to trace their lineage back to Africa. Traditional notions of human evolution in fact subscribe to the idea that human ancestors remained there until roughly 1.5 million years in the past. Then around this time a type of human known as Homo erectus started to emigrate.
Homo erectus was actually first discovered by a paleoanthropologist from the Netherlands named Eugène Dubois. Bearing in mind the work of Charles Darwin, Dubois purposely made for Asia in 1886 in search of human progenitors. And after some five years, he and his colleagues eventually stumbled upon precisely what they sought.
Between 1891 and 1892, in fact, Dubois uncovered several fossils on Java – an island in what is today Indonesia. Retrieved from the sides of the Solo River, these finds included the top of a skull, a tooth and a thigh bone. Dubois claimed that these bones belonged to a species that he initially dubbed Pithecanthropus erectus – later revised to Homo erectus.
Then archaeologists in 1921 uncovered additional evidence of Homo erectus in the Zhoukoudian cave complex in Beijing, China. Here, in a site today named for Peking Man, remains were found that painted a clearer picture of the species. In fact, scientists identified some 200 fossils belonging to more than 40 different beings.
So, in the wake of discoveries suggestive of a species known as Homo erectus, experts had some questions to ask. And during the 1900s opinion was divided within the anthropological community about how Homo erectus related to the evolution of man. Some initially had thought that the species may have derived from Asia, while others had believed that it had come from Africa.
Nowadays, though, there is a stream of thought claiming that Homo erectus developed around two million years in the past. However, evidence of the species roughly dating back some 1.8 million years has been uncovered in Africa and western Asia. So there is still some dispute over where exactly it first came from.
It has also been hypothesized that Homo erectus survived as a species for as long as two million years. This would make it one of the more long-lasting species of Homo known to have inhabited the planet. For context, modern humans – or Homo sapiens – are thought to be only around 250,000 years old.
There has therefore been no agreement within the scientific community about whether or not Homo sapiens evolved from Homo erectus. It is, however, thought to be a possibility that it did. And in that vein, the chances are that the newly discovered Homo luzonensis may itself be related to Homo erectus.
In fact, presently there appears to be two primary strands of thinking as to the origins of Homo luzonensis. The first relates to the aforementioned suggestion that Homo luzonensis derives from Homo erectus. This would mean that the latter species showed up on Luzon island and over time evolved into the former.
A paleontologist named Gerrit van den Bergh from Australia’s University of Wollongong has elaborated on this idea. “You get different evolutionary pathways on islands,” he told the Nature journal. “We can imagine [that] Homo erectus arrives on islands like Luzon… and no longer needs to engage in endurance running but needs to adapt to spend the night in trees.”
Yet the other theory about the origins of Homo luzonensis contends that it evolved from a species with similarities to Australopithecus afarensis. This is a contentious view, as Australopithecus afarensis has thus far only been known to have inhabited Africa. But there are still reportedly notable similarities between it and the recently discovered fossils of Homo luzonensis.
Regardless of Homo luzonensis’ ancestry, though, there are also some other significant questions that need to be addressed. For instance, how is it that this species actually managed to show up on Luzon island in the first place? After all, the island itself has reportedly never actually been joined with the mainland.
One argument suggests that these early humans actually arrived on Luzon island completely by accident. The theory goes that this may have occurred due to a naturally occurring weather event dragging them out into the ocean. Managing to stay afloat by holding onto trees, Homo luzonensis may then have washed up along the shores of the island.
The other assertion states that the early humans actually purposely entered the ocean aboard a type of boat. Some dispute this theory on the ground that early humans had not yet developed an aptitude for sailing, though. But one of the researchers who worked on the paper announcing Homo luzonensis’ discovery has argued otherwise.
“Arrival by accident… is favored by many scholars,” Florent Détroit has stated, according to The Guardian. “But this is mainly because of arguments like, ‘Homo erectus were not clever enough to cross the sea on purpose.’ But the fact is that we have… evidence that they successfully settled on several islands in the remote past in Southeast Asia.”
So there is still so much to learn about Homo luzonensis and its lineage. But the very idea of the species’ existence has already called into question past notions related to human evolution. For instance, some of the fossils dating back 50,000 years suggest that the species existed in the same period as Homo sapiens.
Chris Stringer, an expert on human origins from London’s Natural History Museum, has also suggested that we need to discover how Homo luzonensis died off. He has even questioned whether or not modern humans may have been involved, as reported by The Guardian. “It is too early to say whether the spread of Homo sapiens into the region… might have been a factor in [Homo luzonensis’] disappearance,” he said.
Yet the ability of scientists to answer the questions posed by the discovery of Homo luzonensis will likely require more fossils. And in that vein, the initial discoverer of the species plans to keep searching. Yes, according to Time, Armand Mijares has pledged to resume excavations some time in the near future.
And Mijares is hopeful that his team may discover more sizable fossils or even tools during the next investigation. But already his work has added an additional layer to the perplexities of mankind’s development. For even though his discoveries have raised many questions, ultimately they are sure to lead us to a clearer understanding of human origin.