Islands of Human Evolution

The cast of an H. luzonensis metatarsal

Lannon Harley, ANU

In 2007, archaeologist Armand B. Mijares, of the University of the Philippines in Quezon City, discovered a 67,000-year-old foot bone of an early human relative in a limestone cave on the Philippines’ largest and most populous island, Luzon. While the bone’s exact Homo species was not clear, it was the earliest direct evidence of hominins in this Southeast Asian archipelago. Since the original find, Mijares and an international research team have continued to excavate the Callao Cave Complex in Northern Luzon, where they have found twelve additional early human fossils from the same layer. They have determined that these bones and teeth belong to a distinct hominin species, which they have named Homo luzonensis.

The team found seven teeth, two hand bones, two foot bones, and the shaft of a child’s femur. In all, they represent the remains of three individuals who lived at least 50,000 years ago. The fossils showed a unique combination of ancient and more modern traits—a “very ‘mosaic’ overall morphology,” said paleoanthropologist and team member Florent Détroit, of France’s National Museum of Natural History in Paris.

The teeth of H. luzonensis are particularly small, which suggests H. luzonensis had a potentially small stature. (This can only be confirmed by filling in more of the skeleton.) Their premolars are especially large relative to their molars and showed some features similar to more recent members of the genus Homo, including H. sapiens. Their molars also appear more like ours. The shape of H. luzonensis premolars, however, resemble those of older members of Homo and of Australopithecus, with two or three roots rather than the more typical single root of modern humans. The hand and foot bones of H. luzonensis also resemble those of Australopithecus.

Not far from Callao Cave, other researchers have recently found more signs of hominin activity: 700,000-year-old stone tools and rhinoceros bones with cut marks. These findings in the Philippines and the 2004 discovery on the Indonesian island of Flores of H. floresiensis—all sharing many traits of Australopithecus not found in other species of Homo—raise many questions about human evolution among the islands of Southeast Asia. (Nature)