Since the reporting of the so-called "hobbit" fossil from the island of
Flores in Indonesia, debate has raged as to whether these remains are
of modern humans (Homo sapiens), reduced, for some reason, in stature,
or whether they represent a new species, Homo floresiensis.
Reporting in this week's PLoS ONE in a study funded by the National
Geographic Society Mission Programs, Lee Berger and colleagues from the
University of the Witwatersrand, Rutgers University and Duke
University, describe the fossils of small-bodied humans from the
Micronesian island of Palau. These people inhabited the island between
1400 and 3000 years ago and share some - although not all - features
with the H. floresiensis specimens.
Palau is situated in the Western Caroline Islands and consists of a
main island of Babeldaob, with hundreds of smaller rock islands to the
south west, colloquially known as the ''rock islands." These rock
islands contain caves and rock shelters, in many of which, fossilized
and subfossilized human remains have been found. The specimens
described by Berger and colleagues came from two such caves, Ucheliungs
and Omedokel, which appear to have been used as burial sites.
In both caves, they found skeletons of individuals who would have been
small even relative to other such populations and are approximately the
size of H. floresiensis or small members of the genus Australopithecus.
These fossils were radiocarbon dated to between 1410 and 2890 years
ago. The entrance to Omedokel cave also contained the remains of larger
individuals dated to between 940 and 1080 years ago.
These two caves have provided and will continue to provide a wealth of
specimens, which will need more intensive study. However, preliminary
analysis of more than a dozen individuals including a male who would
have weighed around 43 kg and a female of 29 kg, show that these
small-bodied people had many craniofacial features considered unique to
H. sapiens.
These include: a distinct maxillary canine fossa, a clearly delimited
mandibular mental trigone (in most specimens), moderate bossing of the
frontal and parietal squama, a lateral prominence on the temporal
mastoid process, reduced temporal juxtamastoid eminences and an en
maison cranial vault profile with the greatest interparietal breadth
high on the vault. Thus, these individuals are likely to be from a
human population who acquired reduced stature, for some reason.
It is well established that populations living on isolated islands
often consist of individuals of smaller stature than their mainland
cousins - a phenomenon known as island dwarfism. This is true not just
for humans but for many animals including extinct mammoths and
elephants from islands off Siberia, California and even in the
Mediterranean.
Alternatively, the island may have been colonized by a few small
individuals, between 3,000 and 4,000 years ago who, through extensive
inbreeding, and other environmental drivers, produced a small-bodied
population, which continued to inhabit Palau until at least 1400 years
ago.
As well as having characteristics of H. sapiens, the Palau fossils also
have features seen in H. floresiensis, such as their small bodies and
faces, pronounced supraorbital tori, non-projecting chins, relative
megadontia, expansion of the occlusal surface of the premolars,
rotation of teeth within the maxilla and mandible, and dental agenesis.
Berger and colleagues do not infer from these features any direct
relationship between the peoples of Palau and Flores; however, these
observations do suggest that at least some of the features which have
been taken as evidence that the Flores individuals are members of a
separate species, may be a common adaptation in humans of reduced
stature.
Detailed analysis of the Palau specimens is unlikely to settle
arguments over the status of H. floresiensis as there are features of
Flores man, such as small brain size, not found in the people of Palau.
Nevertheless, they do suggest that at least some of the unusual
features seen in Flores are a result of environment rather than
ancestral heritage.
Above all, the skeletons from Palau should greatly increase our
understanding of the process of island dwarfism in human populations
and of the ancient colonizations of Oceania.