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On 10 April 2019, our extended family got a bit bigger. A study in Nature reported the discovery of a new species of hominin called Homo luzonensis, from the Philippines. My colleague and fellow fossil enthusiast Colin Barras wrote about it for 快猫短视频.
It鈥檚 been five years since the announcement, so I thought now was a good time to revisit H. luzonensis: to see what else has emerged about it in the half-decade since it was revealed to the world, and how it might fit into the human story.
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First, let鈥檚 recap for anyone whose memory of 2019 is less than forensically accurate. (Honestly it feels like 20 years ago.) The remains of H. luzonensis were found in Callao cave on Luzon, the largest island in the Philippines, in the north of the archipelago.
The first fossil, a foot bone, was found in 2007 by a team co-led by Florent D茅troit at the French National Museum of Natural History and Armand Salvador Mijares at the University of the Philippines. It wasn鈥檛 clear what species it belonged to. However, fast-forward 12 years and the team had obtained 12 additional bones: seven teeth, two finger bones, two toe bones and part of a thigh bone. Dating studies suggested some of the remains were 50,000 years old.
This was enough for D茅troit, Mijares and their colleagues to declare this a new species. The bones didn鈥檛 match our species, Homo sapiens, nor did they map onto any other known hominin. Hence H. luzonensis, after the island.
That was five years ago. We鈥檝e learned a bit more since then.
Homo luzonensis
Let鈥檚 start by situating H. luzonensis more fully. If your Asian geography is hazy, the Philippines are south-east of China, in the westernmost part of the Pacific Ocean. Indonesia lies to the south.
The most obvious fact here is that Luzon is a long way from Africa, where hominins originated. However H. luzonensis got there, it鈥檚 a long story.
That story almost surely involves a sea crossing. During the glacial periods, sea levels were lower because so much water was locked up in the ice caps. As a result, many places that are now islands, like Borneo and Sumatra, were connected to mainland Asia 鈥� forming a vast expanse of land called Sunda. However, it seems Luzon was always an island.
The implication is that some population of hominins, wandering vaguely eastwards, made their way to Luzon 鈥� accidentally or on purpose. Isolated on the island, they evolved bodies different to those of other hominins, ultimately becoming the distinct species we call H. luzonensis.
Which hominins were the progenitors of H. luzonensis? This question is tricky, for two main reasons.
Unknown ancestors
First, Luzon has a tropical climate, so it鈥檚 unlikely ancient DNA has been preserved 鈥� and indeed, attempts to extract it from the H. luzonensis remains have been unsuccessful. This cuts off a key line of evidence.
Second, we only have one set of remains of H. luzonensis. This means we don鈥檛 know how long they lived on Luzon. A 2018 study found the earliest known hominin activity in the Philippines on Luzon, in the form of stone tools and butchered rhino bones. These artefacts were 709,000 years old. Conceivably the hominins involved were H. luzonensis or their direct ancestors, but no hominin bones were found so we have no way of knowing. The two findings could be completely unrelated.
This means a wide variety of hominins are in the frame. One candidate is Homo erectus, which was living outside of Africa at least 1.8 million years ago and survived at Ngandong on Java until as recently as 108,000 years ago. It seems distinctly possible that some H. erectus made it to Luzon.
Another possibility is the 鈥�hobbits鈥�, Homo floresiensis, known from the island of Flores in Indonesia. It鈥檚 conceivable that some of them made it to Luzon and then became isolated there. However, there鈥檚 no sign of the hobbits outside of Flores. The timings also may not work: the hobbits probably lived on Flores between 190,000 and 50,000 years ago, so if H. luzonensis turns out to be older than that, the hobbits can鈥檛 be their ancestors.
The third possibility is the Denisovans, whose remains have been found on mainland Asia in the Altai Mountains and Tibetan plateau. Today many people in island South-East Asia carry Denisovan DNA, suggesting the Denisovans roamed Sunda as well as what we now think of as the mainland. Intriguingly, a 2021 study found that groups called Ayta living on Luzon have the highest level of Denisovan ancestry in the world, hinting that the Denisovans visited the island. However, we have few confirmed Denisovan remains, so we don鈥檛 know how long they were around.
Finally, there is the most dramatic possibility: that H. luzonensis is directly descended from an Australopithecus. These earlier hominins have only been found in Africa, but it鈥檚 conceivable that some of them did wander outside the continent. In the original 2019 study, the researchers described a number of attributes of the H. luzonensis remains that are not found in other Homo species but are found in Australopithecus.
Recent studies of H. luzonensis may shed some light.
The latest data
Two studies point to a link with H. erectus. In 2022, D茅troit, Mijares and their colleagues published a study of H. luzonensis teeth. They compared the teeth with those of several other hominins. The crowns of the teeth were most like those of H. erectus in their external shape, while the internal structures were most similar to those of H. erectus and of hobbits. The team interpreted this to mean that both H. luzonensis and H. floresiensis were descended from H. erectus.
In line with this, a 2023 study by an independent group argued that H. luzonensis and H. floresiensis are both similar enough to known H. erectus fossils, and separated enough in time, that we should not be unduly surprised by their existence. Put another way, there was plenty of time for H. erectus populations to evolve into these different forms.
On the other hand, D茅troit, Mijares and their colleagues released a study in February 2023 that has yet to be peer-reviewed, also focusing on the teeth. They measured the layers of cement on the teeth, which are laid down yearly a bit like the growth rings of a tree. This suggested that one of the H. luzonensis individuals died age 31, or perhaps a little older. It also hinted that they had shorter childhoods than modern humans, more like those of chimpanzees.
This could fit with the fact that some of the H. luzonensis remains are pretty small, so, like the hobbits, they may have been small 鈥� in which case it wouldn鈥檛 take them too long to reach maximum size. It could also be evidence of a link with Australopithecus, which was more ape-like than any Homo species.
The Australopithecus idea is clearly the most radical and therefore the one that excites me the most. Nevertheless, I鈥檓 wary of claiming that H. luzonensis is a direct descendant of an Australopithecus. Yes, the similarities are there, but evolution often throws up the same thing multiple times in different species: it鈥檚 called convergent evolution. I would want to see a lot more of the skeleton and a lot more similarities to Australopithecus.
The other obvious issue is that we have plenty of evidence of H. erectus in South-East Asia, and no physical evidence of Australopithecus outside Africa. For that reason, I think H. erectus remains the most likely ancestor of H. luzonensis (although possibly via a Denisovan intermediate, if we assume Denisovans are descended from H. erectus).
But never say never. Maybe we haven鈥檛 found a non-African Australopithecus because we haven鈥檛 looked hard enough. Certainly, it seems odd to say that they were incapable of expanding beyond Africa, when so many other animals did (this is your regularly scheduled reminder that Britain was once home to elephants). A non-African Australopithecus would be a big find, but I wouldn鈥檛 bet my house on its non-existence.
After all, nobody in the 20th century was predicting H. luzonensis or the hobbits, yet here we are. The only thing that should surprise us now is if there are no more surprises.
