Homo luzonensis

A new member of the human genus has been found in a cave in the Philippines, researchers report.

Fossils with distinctive features indicate that the hominid species inhabited the island now known as Luzon at least 50,000 years ago, according to a study in the April 11 Nature. That species, which the scientists have dubbed Homo luzonensis, lived at the same time that controversial half-sized hominids named Homo floresiensis and nicknamed hobbits were roaming an Indonesian island to the south called Flores (SN: 7/9/16, p. 6).

In shape and size, some of the fossils match those of corresponding bones from other Homo species. “But if you take the whole combination of features for H. luzonensis, no other Homo species is similar,” says study coauthor and paleoanthropologist Florent Détroit of the French National Museum of Natural History in Paris. ¹

If the find holds up to further scientific scrutiny, it would add to recent fossil and DNA evidence indicating that several Homo lineages already occupied East Asia and Southeast Asian islands by the time Homo sapiens [modern humans] reached what's now southern China between 80,000 and 120,000 years ago (SN: 11/14/15, p. 15). The result: an increasingly complicated picture of hominid evolution in Asia. ²

But some scientists not involved in the research say it’s too soon to declare the Luzon fossils a brand-new Homo species. Détroit’s group, so far, has been unable to extract ancient DNA from the fossils. So “all [evolutionary] possibilities must remain open,” says archaeologist Katerina Douka of the Max Planck Institute for the Science of Human History in Jena, Germany. ⁴

Implications of H. luzonensis for hominin evolution
The Late Pleistocene hominin fossils from Callao Cave show a combination of dental and postcranial (hand and foot) features that is distinct from currently known species of the genus Homo (Supplementary Table 3). The premolars of H. luzonensis combine size and shape features seen in other Late Pleistocene species of the genus Homo (for example, H. neanderthalensis,  H. floresiensis and H. sapiens) with primitive morphological features of the crown, EDJ and roots, which are typically found in earlier hominins, including Australopithecus and  Paranthropus  (Supplementary Table 3). The molars are extremely small and their external morphology resembles those of H. sapiens and—to a lesser extent—those of H. floresiensis, whereas some of their EDJ shapes show affinities with those of Asian H. erectus. Notable similarities are observed between H. luzonensis and Australopithecus in the anatomy of their manual and pedal elements. The morphologies of the hands and feet of Australopithecus, which are generally described as an intermediate between the morphologies of great apes and modern humans, are typically interpreted either as indicating adaptations to various degrees of bipedalism and climbing and/or suspension or as reflecting the retention of plesiomorphic features in obligatory bipeds. However, the partial and fragmentary nature of the H. luzonensis postcranial elements presently limits further interpretation of its locomotor and manipulative abilities.

The origin of H. luzonensis, as well as its phylogenetic relationships with other hominins present in eastern Asia at around the same time—including H. sapiens, H. floresiensis and Denisovans, and hominins recently discovered in China—remains to be determined. As is the case for most hominins recovered from tropical Asia, attempted DNA extraction from H. luzonensis fossils has been unsuccessful. Direct dates on H. luzonensis tooth and bone samples indicate it was present on Luzon before 50 kyr ago and the recent discovery of stone tools and a butchered rhinoceros in the nearby Cagayan Valley indicates that hominins, perhaps H. luzonensis, have been present on Luzon since more than 700 kyr ago. Clearly, both H. luzonensis and H. floresiensis were present east of the Wallace Line on Luzon and Flores, respectively, at the same time and perhaps even over a similar temporal interval. The skeletons of both species present anatomical traits that are either rare or absent elsewhere in the genus Homo but have similarities with those of Australopithecus. As is the case with the island of Flores, a substantial sea crossing has always been required to reach Luzon from any mainland, even during the lowest sea level periods of the Quaternary period (Fig. 1). The insular nature of Luzon and the Philippine archipelago east of Palawan more generally is reflected in the high rates of endemism recognized in vertebrate faunas. Given the highly endemic nature of the Luzon vertebrate faunas, evolutionary convergences and/or reversals under the effects of insular evolution may explain the distinct anatomy of H. luzonensis; however, further discoveries and more definitive evidence are needed. The discovery of H. luzonensis underscores the complexity of the evolution, dispersal and diversity of the genus Homo outside of Africa, and particularly in the islands of Southeast Asia, during the Pleistocene. ⁷

The mosaic of fossil features that the team interprets as distinctive, for instance, may have been a product of interbreeding between two or more earlier Homo species, creating hybrids, but not a new species.

Or perhaps a small population of, say, H. erectus that survived on an isolated island like Luzon for possibly hundreds of thousands of years simply acquired some skeletal features that its mainland peers lacked, rather than evolving into an entirely new species, says paleoanthropologist María Martinón-Torres. ⁸