The human family just got larger. Bones found in a cave in Northern Luzon in the Philippines have turned out to belong to a member of our own genus, but not our species, nor any species we have seen before. Scientists studying the bones have called their owners Homo luzonensis.
In 2007 a single thigh bone was found in Callao Cave, Luzon, and confirmed to be human (that is, more closely related to us than to any other living great apes) and at least 67,000 years old. The presence of a close relative in the Philippines was surprising, because even at the height of the last Ice Age, the islands were cut off from mainland Asia, limiting the mammals that reached there. At the time it was impossible to tell, however, if the bone came from a Homo sapien who had wandered further than expected, an already known species such as the “hobbits” (Homo floresiensis), or something new.
Now twelve more fossils, from at least three individuals, two adults and a juvenile, have been found in the same cave. The discoveries, reported in Nature, are a mix of hand and foot bones and teeth, the last of which have been found to be at least 50,000 years old. Some of the features, such as the shape of the toe bones, resemble ancient ancestors like Australopithecus aferensis, which died out more than 2 million years ago in Africa. However, other features, such as long narrow finger bones, are more reminiscent of Homo sapiens than even our closer relatives like H. erectus.
Other aspects, such as unusually small molars, are unlike anything we have seen before in the extended human family.
The bones indicate they are from individuals less than 1.2 meters (4 feet) tall, but tell us little about their lifestyle, other than that they probably climbed trees to escape danger or access food.
The Philippines is separated from the Asian mainland by sea lanes almost 100 kilometers (60 miles) wide. During the last Ice Age, however, sea levels were so much lower it was possible to walk from the Malaysian peninsula to Borneo. The island of Palawan nearly touched Borneo, and human fossils estimated to be 50,000 years old have been found there. However, the waters between Palawan and the rest of the Philippines are much deeper, leaving Luzon and the smaller islands ecologically isolated.
Last year much older stone tools, and bones that had clearly been cut with them, were found in a valley not far from Callao. “We know hominids have been on Luzon for at least 700,000 years,” Professor Philip Piper of the Australian National University told IFLScience. However, he added, “We don't know what sort of hominid.”
Piper said among the researchers, the explanation considered most likely is that H. erectus, known to have been in south-east Asia 1.8 million years ago, made it to the Philippines at some point, and evolved into H. luzonensis.
A similar explanation is popular for the Flores hobbits. However, given the limited remains, and the difficulties of extracting ancient DNA in tropical environments, this is still mostly a guess. It's possible an Australopithecus species left Africa millions of years ago, and somehow reached Luzon or H. luzonensis were more recent arrivals. Either way, Piper doubts H. luzonensis' ancestors were technological enough to build boats, instead they likely rafted from Palawan.
The first evidence we have for H. sapiens on Luzon comes from the same cave, around 28,000 years ago, so we don't know if modern humans overlapped with H. luzonensis, let alone had anything to do with their extinction.
Naturally, Piper hopes further digging will reveal more H. luzonensis fossils, but presently there is an unusual obstacle: A chapel has been built inside Cave Callao, and much of it has been concreted over.