Map of the Philippines showing the location of Callao Cave and Tabon Cave. Prepared by Geraldine Cave.
In 2019, what began as a few random finds around the island of Luzon eventually turned the Philippines into a human-evolution sensation. What’s happening there draws a parallel with the discovery of H. floresiensis in Indonesia. Could island South-East Asia be the new evolutionary frontier?
The Filipino connection began a world away in 1888, when a German geologist, Edmund Naumann, noticed a stegodont tooth among the collections in the Anthropological-Ethnographic Museum in Dresden. The tooth was labelled as having originated from the island of Mindanao. Naumann placed the fossil within a new species, Stegodon mindanensis.1 This was the first indication that the stegodont, an ancient, now-extinct mammal, had made it to the Philippines. Naumann’s observations, however, went largely unnoticed, languishing in an obscure publication.
The tooth turned out not to be an isolated find. During the early 1900s, keen-eyed workmen, collectors and geologists occasionally brought the odd fossil tooth or piece of bone into the Bureau of Science in Manila. In fact, right up until the 1930s, random fossil discoveries around Luzon quietly found their way to the bureau to be stored. These included a fragmentary molar of an elephant, a large piece of stegodont bone, a deer horn, thick bone from a large prehistoric turtle, fragments of ivory from a stegodont tusk, and from the mountains of Cagayan, sections of a jawbone (including molars) from a rhinoceros.2
Many of these fossils, once duly labelled and put away, lay forgotten. That is, until 1935, when leading paleoanthropologists Professor Henry Otley Beyer and Professor Ralph von Koenigswald, while attending the second Far Eastern Prehistory Conference in Manila, took the opportunity to delve into the collection at the Bureau of Science. For these professors, as for all researchers, it was an exciting prospect to rediscover fossils in the depths of museums. But more than that, they recognised the importance of what they were doing, and they soon started publishing their findings. By the early 1950s, it had become clear that, as Beyer wrote, extinct rhinoceros, elephants and stegodonts had roamed the Philippines during the Middle Pleistocene ‘not less than 250,000-300,000 years ago’.3
Professor Beyer remained intrigued by the fossils from the bureau and in 1957 invited Professor von Koenigswald back to the Philippines to have a look at the site in Cagayan where the rhinoceros molars had been found. Von Koenigswald undertook the trip with Larry Wilson (who had found additional fossils there), a Mr Shantz (an archaeology student) and DG Kelly (California Institute of Sciences). They found ‘four or five stone implements’ from a Pleistocene level but no Pleistocene fossil bones. Wilson had also discovered in the same place some objects called tektites. This was the second time that tektites had been found in association with fossil bones of stegodont and elephants, the first being the H. erectus site of Trinil on Java.4
Tektites are small pieces of natural glassy objects. They form when a large asteroid or meteorite hits the Earth at such speed that the explosive impact releases enough energy to eject melted soils and rocks out through the Earth’s atmosphere. The melted material cools and solidifies, and the glass-like objects plummet, showering hundreds and thousands of kilometres of terrain.5 The combination of tektites with fossil stegodont and elephant bones at the Cagayan site indicated to Von Koenigswald and Beyer that the Trinil and Cagayan sites were contemporaneous. The stone tools at the Cagayan site, then, were thought to be of Middle Pleistocene age.6
Through the 1950s and 1960s, archaeological exploration and large-scale excavations proceeded apace in the Philippines, with the country’s National Museum (the new incarnation of the Bureau of Science) taking a leading role under the head of the Anthropology Division, Professor Robert Fox. But it was not for several decades that things really took off in terms of human evolution research. Two key discoveries were eventually made, the first of which concerned a long-dead rhino that left the scientific community reeling.
In 1999, Professor John de Vos (Natural History Museum, Leiden) decided to accept a longstanding invitation from Angel Bautista (Senior Researcher at the Archaeology Division, National Museum University of the Philippines)7 to visit the Philippines. De Vos recalls:
I first visited the sites from which we know that there are fossils. The most promising site was Cagayan Valley, but I didn’t have money to excavate there. There I found artefacts, bones of stegodont, elephant and tektites.8
De Vos couldn’t forget those bones, but it would be fourteen years before he could return:
Later I had a French PhD student, Thomas Ingicco, a zooarchaeologist, who was on an exchange research programme [in the Archaeological Studies Program at the University of the Philippines]. He invited me to the Philippines in 2013 to give some lectures. After delivering my talks I had some time and some money to go with Thomas to Cagayan Valley. There we found a species of the same genus Celebochoerus [an extinct form of wild boar] as in Sulawesi. In 2014 I arranged some money by inviting Gert van den Bergh, my former PhD student, George Lyras from Athens, a student of mine, and of course Thomas. They brought enough money in and we could excavate. At about 2m deep we found a partial skeleton from a rhino with butchery marks, artefacts and tektites. It was published in Nature.9
Map of the Philippines showing the location of Callao Cave and Tabon Cave. Prepared by Geraldine Cave.
It was the butchery marks, found on some ribs and legs, that made these bones so special. Someone, or a group of people, had deliberately cut those bones, probably to strip off some flesh and eat it. Someone had also smashed the rhino’s two front-leg bones, perhaps to access the highly nutritious marrow inside. The culprit was no modern human, though, because the bone is dated to 709 000 ± 68 000 years ago.10 Who were these rhino-eating hominins?
Also on Luzon, the Filipino archaeologist Armand (Mandy) Mijares (National Museum of the Philippines), who had been excavating caves for many years, became particularly interested in the period of human history when, around 10 000—12 000 years ago, people in several parts of the world started switching from hunting and gathering to farming. He wanted to know the ‘how’, ‘when’ and ‘why’ of this transition in his own country, enormous questions requiring a lot of research, which saw Mandy start his PhD in 2003 at ANU under Professor Peter Bellwood.
With a lot of archaeological knowledge and experience behind him, Mandy’s choice of location to dig was Callao Cave, about 300 kilometres north of Manila. It was one of forty-three caves identified by the National Museum of the Philippines as having archaeological potential during extensive surveys in 1976–77.11 The cave is impressively large, the biggest in the area, and it is quite a tourist attraction. It has ceiling heights ranging from 10–45 metres and is so spacious that a chapel was built in the second chamber in the 1970s. Archaeologist Maharlika Cuevas and a team from the National Museum had partially excavated it in 1979 and 1980.12
Mandy’s team headed to the cave in 2003. But how do you decide where to start digging in such a huge cave? Peter Bellwood had the answer. Pointing to a spot at the base of the east wall of the cave, he said: ‘There’s a nice flat area over there, next to the cave wall. Good potential for discovering archaeological remains. Let’s get stuck in!’13 And dig they did. At a depth of 1.3 metres they found stone tools, burnt animal bones and a hearth. When these were dated, the results showed they had come from Late Pleistocene strata that was 25 968 ± 374 years old—way before farming emerged anywhere in the world.14
To further investigate the promising finds in Callao Cave, a partnership was established between the University of the Philippines Archaeological Studies Program, the National Museum of the Philippines and the Australian National University. At this time there was no intention of exploring the earlier history of the cave.15 The focus remained firmly on the research issue: the transition to farming in the Philippines.
Mandy happened to be back at ANU in 2004, where he was continuing his analyses, when Mike Morwood turned up to give a public lecture about a new species, H. floresiensis, that his team had discovered in Liang Bua cave on Flores. Most of us were astonished by the small, archaic-looking hominin bones Mike talked about. What impressed Mandy, however, was the sheer depth to which the Liang Bua team had excavated: 11 metres. Mandy realised then and there that ‘you just dig deeper’, and he thought: ‘I can do this!’16
By 2007, Professor Bellwood had secured an ARC grant that enabled the team to return to Callao Cave to dig deeper. A decade later, Mandy recollected: ‘Inspired by the work of Mike Morwood at Liang Bua, Flores, I went back to Callao and excavated my original trenches to a greater depth with the hope of finding evidence of early hominin activity.’17
Callao team, 2007; from left to right: Sandy De Leon, Archie Tauzon, Mandy Mijares, Nida Cuevas, Domeng Pagulayan and Kardo. Image provided by Armand (Mandy) Mijares.
Starting where the 2003 dig had left off, the team soon encountered a high concentration of bones in a thin layer lying 2.7–2.9 metres deep.18 This was well below the level in which they had earlier discovered the hearth, burnt animal bones and tools. At the end of the fieldwork season, the team duly packed up all the bones they’d found and took them back to the University of the Philippines to be identified. Zooarchaeologist Associate Professor Philip Piper had just joined the Archaeological Studies Program at the university.19 Mandy set the box of bones from Callao Cave on Phil’s desk and asked him to identify the bones therein, all 807 of them.
Where does a zooarchaeologist start? It’s not just a matter of picking out each bone, holding it up and figuring out its species. A zooarchaeologist needs to understand what happened to the bones before they were excavated, how they got into the cave, as well as what happened to them afterwards, and anything else that might be of future importance. This proved a challenging task. As Phil explains: ‘The bones were all covered or partly covered in hard sediment and they were very broken up because bones in caves get fragmented by trampling, or when transported by water, and when they get buried [by sediment].’20
An elaborate series of details was recorded for each bone, including measurements, and they were inspected for cut marks or trampling marks, and for evidence of being water-worn. Most of the 807 bones were from deer, some were pig bones, and there were also two tooth fragments from an extinct water buffalo. But Phil was on the lookout for something special, because when Mandy had handed over the box of bones, he’d given Phil a heads-up: ‘There’s a strange one in there, might be human.’21
And there it was—a possible human foot bone, albeit covered in a thin layer of calcite and broken into two parts. Phil immediately called Mandy: ‘Hey mate, you have human remains!’
‘What? Really?’
‘Yes, you have human remains.’
It was beers all round that evening.22
Tiny though this bone was, it was particularly significant because it had to be older than the material from the 2003 excavation that was dated to the Late Pleistocene. ‘We knew we were onto something,’ recalls Phil.
The team did a bit of wishful thinking, guesstimating the bone’s age as possibly at 50 000—60 000 years old. At that time, the earliest date for modern humans in the Philippines was 48 000 ± 10 000 years old, derived from a human tibia (lower leg bone) excavated at Tabon Cave.23 The team’s initial hope was that their bone would date to earlier than this.
Phil and Mandy now called in Dr Florent Détroit (Musée de l’Homme, Paris), an archaeologist and bone specialist who had long been involved in Philippines archaeology. Working with Florent were master’s student Guillaume Champion and, later, Dr Guillaume Daver (Université de Poitiers, Poitiers, France). Florent says:
I first visited Callao during the 2007 excavation, after our excavation season in Tabon Cave in March 2007, with several European masters students, including Clément Zanolli and Julien Corny at the time, and then I went again some months after to Manila to continue the work on Tabon. So, it was after visiting Callao Cave … that Mandy and Phil came to me with this possible human foot bone that Phil identified among the animal remains found in a deep layer at Callao … It was indeed a human bone: it was the 3rd metatarsal.24
The metatarsals are the long bones of the foot, the ones that join the ankle to the toe bones.
Clément, then a master’s student, was there at the time: ‘I still remember the puzzled face of Florent when he saw the metatarsal in the aluminium foil it was kept in at that time, and he recognised the bone as belonging to Homo but with unusual features for modern humans.’25
It was not a straightforward matter to study the bone. Ideally, the layer of carbonate would be physically removed, but as Florent explains:
Actual cleaning of fossils has always been a very ‘dangerous’ step in the preparation of the fossils so that they can be studied, measured, etc., especially when they are encrusted by carbonates, because the bone (even fossilized) just beneath is most of the time more fragile than the carbonate.26
So instead of physically cleaning bones, researchers these days use sophisticated CT imaging techniques. Florent continues:
This is really mandatory to be sure to preserve the integrity of all our precious fossils! [Using CT images] you virtually remove this extra material. You obtain a perfectly (though only virtually) cleaned fossil that you can study, analyse and even use to produce 3D printings of the cleaned fossils if you want to handle them and compare them visually with other fossils or casts.27
Expecting the bone to be modern, Florent and Guillaume were surprised to find it had some non-modern characteristics. As Florent recalls: ‘Many features of this bone do not fit into the variation known for H. sapiens (including fossil H. sapiens).’28 For example, the base of the modern human metatarsal is flat or slightly concave, while the Callao Cave bone is convex. The Callao Cave bone is also slightly convex in side view and it has a ridge running along the surface. Apart from its small size, the most striking thing about it is its unusual proportions.29
These anomalies were perplexing. From whom did this bone come? To get a handle on this question, Florent and Guillaume compared the metatarsal to the foot bones of primates of medium-to-large body size living in island South-East Asia: macaques, orangutans, gibbons, and Homo, including H. floresiensis. In these sorts of analyses, bones from the fossil record are also included. For foot bones this is tricky because so few have been discovered. However, there were some for the earliest species in our genus, so a H. habilis metatarsal was added into the mix.
The team found that the Callao Cave foot bone was smaller than those of orangutans, and larger than those of gibbons and macaques. Its length was similar to the metatarsals of Homo, particularly the small-bodied Philippine Negritos,30 H. habilis and H. floresiensis. Its particular form, though, was different from anything previously described in fossil specimens of the genus Homo from eastern Africa, southern Europe or the Caucasus. Palaeoanthropologists are wisely reluctant to declare a new species based on a single enigmatic foot bone. The team provisionally attributed the foot bone to a Pleistocene—but probably a small-bodied—human group.31
It was increasingly becoming important, then, to directly date the foot bone. It turned out to be 67 000 years old32—even older than the team’s earlier wishful-thinking guesstimate. Such an early date for humans in the Philippines was quite a find.
The team knew they needed more bones of this mystery group. But when they returned to Callao Cave in 2009 to continue the excavations, they found, well, nothing.33 Subsequent excavations in 2011 at first did not seem to be going too well either, in that no-one was finding any fossils. Mandy felt despondent until two things happened. First, a foot and a hand bone were recovered from sieving.34 Sieving is an essential process in which very patient archaeologists sieve all the soil removed during the dig—it sounds tedious, and it would be except for the camaraderie of your fellow sievers. The objective is to find any items that might have been overlooked as the team excavated. This is no reflection on the archaeologists: bones and artefacts can be unrecognisable as they are dug up, especially if, as occurs in Callao Cave, there is a high clay content that adheres to bones and artefacts. The process is that the soil is first dry-sieved through a 4-millimetre mesh. The material that does not go through is then sieved again using water to dissolve the clays and reveal what lies beneath.35
The second bit of excitement occurred when Phil Piper saw an upper leg bone sticking out from under a rock. On carefully extracting it, he saw that it was from a juvenile and he recognised it as at least primate-like.36
More fossils were to come. Mandy recalls that one lucky student, Archie Tauzon, who had a penchant for listening to the 1960s surf-rock band The Beach Boys as he excavated, discovered a fossil, then another, and another. Something strange began to happen—every time someone in the team played The Beach Boys, they seemed to find another fossil.37
One of the fossils was a pedal phalanx, or toe bone. Florent immediately noticed its ‘incredibly marked longitudinal curvature’.38 That is, the toe bone was curved from top to bottom, unlike ours. Some teeth were then discovered. Florent, who was in the excavation square at the time, recalls:
Callao Cave excavation (2011); from left to right: Florent Détroit, Archie Tauzon and Mandy Mijares. Image provided by Armand (Mandy) Mijares.
When we found the teeth, I immediately noticed their very small size and some striking features such as the 3-rooted premolars. All these features which could be easily observed immediately … gave me the feeling that the assemblage would most probably not fit into the frame of the species H sapiens.39
Over just a few days in August 2011, eleven fossils were extracted from the thin, concentrated bone layer.40 What was being uncovered in the Philippines was starting to shape up very much like the discovery of H. floresiensis. And the Callao Cave discoveries could well result in a similar bombshell. But at the time, the finds were a well-kept secret. So it came as a complete surprise when, on 31 August 2012, Professor Peter Bellwood popped into the office of Colin Groves at ANU, where Colin, Bill Jungers and I were discussing our H. floresiensis project. He casually said, ‘Mandy’s here. From the Philippines. He’s brought an upper [third] molar from their excavation at Callao Cave that Rainer is going to date. Come and see.’
Mystified but highly curious, we hotfooted it across to the dating lab run by Professor Rainer Grun in the Research School of Earth Sciences. Mandy and Phil had just walked over there. The tooth was tiny—we thought it the smallest adult tooth we’d ever seen, possibly smaller than H. floresiensis.41 This was the ‘exciting stuff ’ Mike Morwood had predicted back in 2005 in the wake of the H. floresiensis discovery: ‘Island South-East Asia—you’ve almost got a laboratory situation. Different islands, different environments, hominins could have got there at different times. What a fantastic research prospect! This is exciting stuff.’42
But there was more. Later that day, Mandy and Phil showed us images of five other teeth excavated from Callao Cave. In one image, three molars and two premolars were lined up, as they would sit in the palate. Seeing these clinched our initial impressions: we knew that this must be one tiny new hominin. Colin, Bill and I tried to get our heads around what this discovery meant for human evolution, feeling privileged to have been shown the premolar and the images of the other teeth. We could certainly well understand why Mandy and Phil really wanted the tooth dated, bringing it direct from the Philippines for that purpose.
The ANU Research School of Earth Sciences team undertook U-series dating, for which they laser-drilled a row of twelve minute holes into the tooth to extract the datable material. It sounds a bit destructive to drill into a fossil, but at 0.2 millimetres wide and 1–2 millimetres deep, the holes are tiny; they take up only a minuscule bit of space and can hardly be seen by the naked eye. The age of the Callao Cave tooth turned out to be a minimum of 50 000 years. So a tiny hominin lived in the Philippines fairly recently, in human evolutionary terms, and at the same time as modern humans. This really was looking like the H. floresiensis scenario.
When the Callao Cave team returned to the site in 2015, they employed their tried-and-true fossil-finding technique. And while playing The Beach Boys, they discovered an upper third molar. They now had three individuals represented among the remains.43
The fossil count as of 2020 was seven teeth, two hand bones, two foot bones and the femur shaft.44 As Phil and Mandy had shown Colin, Bill and me back in 2012, five of the teeth were from one individual. It was possible to know this because each fit neatly beside the others, so these teeth would have been inside the same mouth.
The team now had a foot bone and some teeth with primitive features. These were unlikely to be from a modern human, as the researchers had thought was the case with the foot bone back in 2010. This called for a team rethink about the identity of the Callao Cave remains, examining each element separately and then putting it all together.
Mandy first recruited two experts in tooth structure and form, introduced above: Dr Clément Zanolli, now a researcher from the Paris-based French National Centre for Scientific Research and also the Université de Bordeaux, and Dr Julien Corny from the Musée de l’Homme. Clément is adept at interpreting the internal structure of teeth from scans, and Julien’s expertise is the external, or outside, morphology of the teeth. Clément observes:
First we noticed modern-like features of the teeth: they are small and have a simple form. But the two premolars have three roots. This doesn’t occur frequently on moderns and even in the archaeological record they are rare, but they are often observed in fossil hominins. So this was our first clue that the teeth are more primitive than modern humans.45
So far, so intriguing, but it was time for more-comprehensive investigations. Zanolli and Corny’s first approach was to compare the teeth with those of H. erectus. Recapping our evolution history, H. erectus is known from Java, Indonesia and, as we saw in chapters 1 and 3, is considered by some to be the ancestor of H. floresiensis. Could it also be the ancestor of the Callao Cave hominin? The two researchers noted that a group called ‘late H. erectus’, which might have survived on Java until just 143 000 years ago,46 had third premolar teeth with the same three-rooted pattern as the Luzon teeth. But H. erectus teeth are very large. Zanolli and Corny’s thinking was that the Luzon hominin could possibly be a dwarf form of late H. erectus, much as had been proposed by some to explain the origin of H. floresiensis.
Another idea they considered was whether it could be a Denisovan, which was identified by DNA from a finger bone excavated in Denisova Cave, Siberia (see Appendix A). The Denisovan teeth are larger than those of H. erectus and thus much larger than the Callao Cave teeth. The Denisovan molars also have a more complex form.47 Clément: ‘We don’t see anything of the Callao Cave teeth in the Denisovans, so we discarded this idea.’48
Zanolli and Corny now broadened their comparisons to include the teeth of A. afarensis, A. africanus, H. erectus, H. floresiensis, H. naledi, Paranthropus, early Homo, the Neanderthals and modern humans. Professor Yousuke Kaifu (National Museum of Science, Japan, and the University of Tokyo) kindly provided the team with scans of one of the H. floresiensis premolars to include in their analyses. The French researchers have found that the shape of the Callao Cave upper molars as a whole is unique. Not only are they small, but they are narrow from front to back, unlike anything in our genus, Homo, the australopithecines or Paranthropus. Yet some internal structures, and the form of the lumps and bumps on their crowns, resemble modern human teeth.
The premolars are large relative to the molars, more so than seen in H. floresiensis and other hominins, except Paranthropus. They also have some primitive features, some of which are seen on H. floresiensis and some of which are not. The premolars have multiple roots, spread widely as found in Australopithecus, Paranthropus and the earliest species in our genus, Homo, and H. erectus. One of the premolars, thought to be an upper fourth premolar, has three roots, which is rarely found in fossil hominins and H. sapiens.
If this sounds complicated, spare a thought for the researchers trying to figure it all out. Overall, the odd size of the premolars compared to the molars and the smallness of the Callao Cave teeth is a pattern not seen in any other species of Homo.49 Clément sums it up: ‘The molars of H. floresiensis and H. luzonensis are modern-like but their premolars having three roots—that’s old.’50
Bones from feet are also useful when looking for similarities and differences between species. But one of the three foot bones excavated in Callao Cave is proving perplexing; ‘bizarre’ is how Florent Détroit describes it.51 It is very curved when you look at it side-on, nothing like what we see in the Neanderthals, H. naledi or H. floresiensis, and it does not have the ‘hourglass’ form of our toe bones. Phil Piper notes that it ‘has a remarkable resemblance to 3.2 million-year-old Australopithecus afarensis—really intriguing!’52
Another toe bone discovered in the excavations is an intermediate pedal phalanx, which is the toe bone that joins with the tip-most of the toe bones. Unfortunately, these toe bones are not particularly useful in species identification because they are variable, even among H. sapiens.53
The remaining foot bone is the one that first alerted the team to the antiquity of humans in the Philippines. It is the third metatarsal that the team published on in 2010, provisionally placing it in H. sapiens.54 Since then, however, the third metatarsal of Australopithecus sediba has been described. The Callao Cave bone shares some similarities with this two-million-year-old extinct hominin from Africa.55
The Callao Cave excavation yielded two finger bones. One is a middle finger bone, technically known as an ‘intermediate phalanx’, the bone that fits between the first- and second-finger knuckles. It is from the left hand of an individual. It is flat as well as incredibly long for a supposedly small bodied hominin,56 and it has characteristics seen in the australopithecines and to a lesser extent H. habilis, but not in other Homo.57 It is relatively longer than that of H. sapiens, A. afarensis, the Nariokotome Boy (also known as Turkana Boy),58 and H. floresiensis.59
The other finger bone is a distal phalanx, one of the tip-most finger bones. The shape of this bone is within the range of H. sapiens and the australopithecines but it’s unlike the finger bones of H. floresiensis and the Neanderthals.60 The Callao Cave fossils are proving to be a quite a complicated puzzle.
The upper leg bone that was found protruding from under a rock in Callao Cave is frustratingly incomplete. With the upper and lower parts missing, all that can be gleaned about this bone from CT scans is that it was the bone of a growing individual. The plan now is to get a better handle on the internal characteristics of this bone. As Clément explains:
The femur is very interesting because even if it is an infant it still probably retains information internally. So from the bone thickness, for example, we can infer its locomotion, if it walked on all fours or on two legs, and the way it was walking. We can also use the foot and hand bones in this way. This is just the start of our work.61
Early on, the fact that the enigmatic Denisovans were identified from DNA drawn from a single finger bone prompted the hope that DNA might be similarly preserved in the Callao Cave bones and teeth. Attempts at extracting DNA from another hominin species in the tropics, H. floresiensis, had had disappointing results; none was preserved. Nevertheless, the H. luzonensis team figured it was worth a try, and Mandy and Florent took the upper third molar to the Max Planck Institute for Evolutionary Anthropology in Leipzig in 2013. Very limited DNA material was recovered from this tooth, however. The Max Planck Institute wanted other hominin remains from the excavations, but Mandy considered the technique too destructive given the small number of hominin remains they had recovered from the cave.62 So he came up with an alternative: to have DNA tests performed not on the precious hominin bones but on the animal remains found in the bone layers. ‘So I first sent cervid teeth for them to test if they can extract DNA,’ he says. ‘Unfortunately this also failed.’63
It is therefore not worth testing for DNA in the H. luzonensis hominin remains, at least not in the conventional way. But there has been a remarkable recent development in DNA research. Dr Viviane Slon and colleagues have been able to isolate DNA from, of all things, cave sediment.64 This they did for caves in France, Belgium, Croatia, Spain and Russia, including the famous Denisova Cave. They have shown that cave sediments contain lots of DNA, including traces of hominins. For example, Neanderthal DNA has been identified in caves that also contained Neanderthal bones, but it has even been found in caves with no signs of Neanderthal visitation. DNA from animals such as hyenas, bovid, deer, horses and related animals that visited the various caves has also been found.
Mandy is inspired by the fact that DNA can be retrieved from cave sediments. In time, he and the team plan to utilise this discovery and collect soil samples from Callao Cave for DNA testing.65 What a sublime breakthrough it would be if DNA in soil is preserved under tropical conditions. Could we eventually get H. floresiensis DNA in this way?
But back to the Philippines. The particular mix of characteristics observed in the Callao Cave hominin remains has not been seen in any other species: this suite of teeth and bones is unique to this group. Under the International Code of Zoological Nomenclature, the researchers involved declared this group of fossils a new species: H. luzonensis, named for the island on which they were found.66 This is exciting, but even more it demonstrates that there were two small, archaic hominin species living in island South-East Asia at about the same time.
In terms of current thinking around human evolution, the Luzon connection has other implications. We see characteristics in H. luzonensis that were present in species that existed more than two million years ago in Africa, just as we saw for H. floresiensis. Yet both H. luzonensis and H. floresiensis are known from relatively recently (geologically speaking) times, and both are half a world away from Africa. We have been able to hypothesise where H. floresiensis fits on the human evolutionary tree because so much of its skeletal form is available to us. However, although most of the H. luzonensis fossil material is clearly diagnostic, and there is ample evidence for it being a new species of Homo, there are not enough body parts to make a call about where it fits on the tree or who its ancestors might have been. To resolve this, we need a few more clues from a skull or jaw or two; some leg and arm bones and a shoulder bone would help, too. Fortunately, archaeologists and their colleagues are a passionate, optimistic and patient lot. It looks like the Callao team will be well funded and able to return to the cave to excavate for many fieldwork seasons to come.
We might not know where H. luzonensis fits on the family tree, but we do know something about its behaviour. When studying those 807 bones from the excavation in Callao Cave, and knowing that no stone tools had been discovered in the layers that bore the hominin bones, Phil Piper noticed something unexpected. ‘We’ve got bones with cut marks. Not many of them, but what we have is really lovely,’ he explains. ‘I say lovely because the marks are very clear. There is no ambiguity about them.’67
Eleven of the deer and pig bones had cut marks on them. To investigate these, the bones were placed under a scanning electron microscope (SEM). This tool, which can magnify an object from around ten times to up to 30 000 times, can create images of otherwise invisible worlds regarding anything from fungi to stones and bones. And the images produced look three-dimensional, which is one of the beauties of this process. Phil could see a distinctive ‘V’-shaped incision that is typical of human-made cut marks. Also visible were ‘shoulder effects’ along the outside edges of these cut marks, a typical consequence of someone using stone tools to deliberately cut bone. There were also incisions running parallel to the main incision, caused by imperfections in the cutting edge of the blade.68
This means that these were the remains of hunted or scavenged animals. So despite not having many hominin fossils, Phil has found out that the bones from the excavations are at least partially left over from hominin activity, and importantly, that H. luzonensis was a tool-using hominin.
Many puzzles remain. Where are the tools that produced the cut marks on the bones? The Callao Cave team suspects that the answer to this might well be related to the nature of the archaeological record. The configuration of the bones into ‘alignments’ within flow channels in the cave suggests that they were transported further into the cave by wet-season water action from what is now the cave entrance area. What might have happened is that the stone implements, being heavier, remained closer to where they were discarded. This is a hypothesis at the moment. It could be that the hominins used organic implements, but some details of the cut marks suggest stone was used.69
With the fossil remains of this new species being found in a cave, it would be easy to assume that these hominins were living right there. After all, Callao Cave is huge, with an inviting massive entrance, and offering safe and relatively salubrious accommodation. Mandy has been thinking about the form of the cave, though. For a long time, a large slab of rock on the floor of the cave near the entrance was thought to have fallen from the ceiling. But Mandy has concluded that it was part of a wall that collapsed during the mid-Holocene (a period that extends from roughly 7000 to 5000 years ago), opening up a walk-in entrance well after the bones of H. luzonensis had accumulated in the cave.
With this possibility in mind, Mandy suspects that before the wall collapsed the cave was a sinkhole: ‘I don’t think H. luzonensis was living there—I think the bones were washed in. There was no entrance before the mid-Holocene. Even the animal bones have been eroded, evidence that they were washed in.’70
During the next fieldwork season, the team will try to find out from where the slab fell. Now there’s a thought … I wonder what they’ll find under the slab?
And we can’t forget about those rhino bones with ‘butchery marks’ discovered by Thomas Ingicco and colleagues. Who were those rhino-eaters? While it is tempting to think they were H. luzonensis’ forebears, we simply cannot assume this. They are, after all, 709 000 years old, around 659 000 years older than H. luzonensis. At the moment, we have no evidence for any hominins in the Philippines during the 659 000 years between the rhino hunters and H. luzonensis.
H. luzonensis certainly presents us with a fantastic research project with a very promising future. We know that with the generous support of the University of the Philippines and the country’s Commission for Higher Education, a substantially larger team will return to Luzon to further excavate Callao Cave and others in the region. And it is exciting to know, as I understand Mandy has confirmed, that our Beach Boys–playing, fossil-finding Archie Tauzon will be there when they do. Idly thinking, I have planned the playlist for the best results: ‘Wouldn’t It Be Nice?’, ‘I’m Waiting for the Day’ and ‘It’s Just a Matter of Time’. And when more fossils are found: ‘Celebrate the News’.
Despite being on many digs, I have never found a fossil. This is always a thrill for anyone in the world of archaeology, so I live in hope. In the meantime, one thing I’ve always been curious about is what happens behind the scenes when archaeologists find fossil bones. Do they show people? Do they ask other experts for their opinions? Or do they keep the discovery a secret until they publish on it?
I took the opportunity to ask Dr Florent Détroit these questions when I met him in Brisbane in June 2019 at the Asia-Pacific Conference on Human Evolution. Florent first responded that, yes, his team did show the H. luzonensis fossils to colleagues:
We had various reactions about the fossils, but I can say that all of them [the colleagues] were quite puzzled after seeing them. Some colleagues were very doubtful, telling me that they were probably from a large primate, but not human. But since we know of no other primate than H. sapiens—and macaques, most probably introduced by humans—in the Philippines, they would have belonged to an unknown species of large primate that was morphologically very close to a hominin, and able to cross the sea gap and settle on Luzon island … which does not sound [like] a very parsimonious hypothesis.1
Others thought that the fossils might correspond to ‘abnormal’ H. sapiens, though Florent was quick to add that this was not the same kind of argument as those published during the H. floresiensis debate (see chapter 3). Instead, behind one or two people’s view that H. luzonensis might be H. sapiens was the notion of widening the definition of H. sapiens to include Neanderthals and other recent hominin species.
On the other hand, Florent commented: ‘Some were very enthusiastic, seeing a clear parallel with H. floresiensis from Flores Island.’ Still others wanted to see a skull before they would accept that the fossils represented a new species, to which Florent’s response was: ‘Well, I clearly do not agree with those palaeoanthropologists who think that only skulls are good and interesting for human evolution.’2
In chapter 2 we saw the uproar when H. floresiensis was announced. Mandy and the team expected a similar reaction over H. luzonensis, but this hadn’t happened. ‘We had some concerns when we published because of the controversy over H. floresiensis, but so far, nothing,’ he said, adding with a smile: ‘We’re hoping to get at least some controversy!’3
I can see his point. It is well understood that science thrives on robust discussions, and human evolution is no exception to this. Perhaps H. floresiensis paved the way for acceptance of the late survival of hominin species in island South-East Asia. But news of H. luzonensis was published only recently, and rarely do announcements of new hominin species go unchallenged. Maybe, then, it is a case of ‘Watch this space’. The team might yet have to face the controversy it expected.
