"The Hobbit" was a distinct species that adapted to an island habitat.
Homo floresiensis, our 3-foot tall hominin cousin also known as “The Hobbit,” lived approximately 18,000 years ago on the Indonesian island of Flores. There has been a great deal of debate about whether the skeletal material was from a unique species as originally described or was in fact a human with a growth disorder.
In the new edition of Science (subscription required), Matthew W. Tocheri and colleagues have analyzed the wrist bones of this controversial specimen and determined that the species retains a primitive morphology from before the origin of modern humans. Wrist elements can be powerful diagnostic tools in classification because the bones are so numerous and can undergo evolutionary changes through both adaptive pressures (such as morphologies necessary for grip structure or style of locomotion) or because of neutral changes as the result of reproductive isolation.
As the authors described the bones in the article released today:
Each is well preserved and shows no signs of pathology or abnormal development. . . . [T]hese three articulating bones display none of the shared, derived features of modern human and Neandertal carpals. Instead, they show the general symplesiomorphic pattern exhibited by all extant African apes, as well as fossil hominins that preserve comparable wrist morphology and date before 1.7 Ma.
A symplesiomorphy is any trait that exists in multiple living species and also in the most recent common ancestor of those species. Tocheri and his team determined that three of Homo floresiensis’ carpals (the trapezoid, scaphoid, and capitate) have more in common with living apes and extinct hominins (such as Homo habilis, Homo erectus and the Australopithecines) than they do with either modern humans or Neandertals. This places them as a distinct species whose lineage branched from the human family at least 1.7 million years ago and which lived contemporaneously with modern humans.
Homo floresiensis likely evolved from a population of Homo erectus that migrated into South East Asia. There is evidence from Sangiran and Mojokerto in Java (Indonesia) for three cranial specimens of Homo erectus from between 1.6 to 1.8 million years ago. Populations of erectus are known to have been in Zhoukoudian, China until sometime between 500,000 and 230,000 years ago. One population may have ended up trapped on the Indonesian island of Flores as the seas rose following the Gunz or Mindel glaciation (roughly 690,000 and 125,000 years ago respectively). The species then underwent a selection pressure for insular dwarfism, in which individuals are selected for smaller stature in order to adapt to the more limited resources that island habitats offer (examples include dwarf elephants from Malta or Crete, Channel Island mammoths and the pygmy dinosaur Europasaurus).
In this way, perhaps our smaller hominin cousins became the original cast of Survivor. Isolated on a remote island, cut off from the resources they'd formally been accustomed to and pitted against the elements in a life or death struggle. However, unlike the modern human contestants, our hobbit cousins didn't rely only on their wits and endurance in order to survive. Homo floresiensis adapted with their environment rather than trying to be masters of it. By doing so they ended up being the last remaining survivors of an ancient hominin lineage. If only they'd been able to survive a few thousand years longer. What we might have learned from each other would have been truly staggering.
Matthew W. Tocheri, Caley M. Orr, Susan G. Larson, Thomas Sutikna, Jatmiko, E. Wahyu Saptomo, Rokus Awe Due, Tony Djubiantono, Michael J. Morwood, and William L. Jungers. (2007). The Primitive Wrist of Homo floresiensis and Its Implications for Hominin Evolution. Science 21(317):1743-1745. DOI: 10.1126/science.1147143