A single bone
In 2007, an archaeological team led by Armand Salvador Mijares was excavating in Callao Cave on the island of Luzon. They discovered a single, small foot bone—a third metatarsal from a right foot. Using uranium-series ablation, the bone was dated to a minimum age of 66,700 years old, making it the oldest known human fossil in the Philippines at the time. The bone's gracile structure was consistent with the genus Homo, but its specific species was unclear. Morphologically, it was similar to small-bodied Homo sapiens but also fell within the size range of earlier species like Homo habilis. This lone bone represented the first direct evidence of a human presence on the island so long ago.
The discovery was puzzling because Luzon has always been an island, never connected to the mainland by land bridges. This implies that the ancestors of "Callao Man" must have made an open-ocean crossing, a significant technological feat for any hominin of that era. The find predated the previous oldest human remains in the Philippines, the 47,000-year-old Tabon Man from Palawan island.
A new branch of humanity
Subsequent excavations in the same stratigraphic layer of Callao Cave between 2011 and 2015 yielded twelve more hominin fossils. These remains included teeth, two finger bones, more foot bones, and a partial femur, belonging to at least two adults and one juvenile. In 2019, analysis of this collection of fossils led Florent Détroit and the team to announce a new species: Homo luzonensis.
The bones display a unique mosaic of features from different hominin lineages. The teeth are small, with molars that are even smaller than those of Homo floresiensis, the "hobbit" species from Indonesia. The premolars have characteristics, such as three roots, that are more similar to much older hominins like Australopithecus. The finger and toe bones (phalanges) are distinctly curved, a primitive trait also seen in australopithecines that suggests an adaptation for climbing.
Small teeth and bones suggests Homo luzonensis was a small-bodied hominin, possibly under four feet tall. This points to a phenomenon known as insular dwarfism, where species isolated on islands with limited resources evolve smaller body sizes. This process also likely occurred with Homo floresiensis on its island home. The existence of H. luzonensis shows that human evolution in island Southeast Asia was a complex process, with multiple distinct hominin species co-existing with early Homo sapiens.