More biology articles in the 'Biology' category

Skull cast and cast of the endocranial cavity (endocast) from the Royal
College of Surgeons in London of a modern adult human who suffered from
What may well turn out to be the definitive work in a debate that has been raging in palaeoanthropology for two years will be published in the November 2006 issue of Anatomical Record.

The new research comprehensively and convincingly makes the case that the small skull discovered in Flores, Indonesia, in 2003 does not represent a new species of hominid, as was claimed in a study published in Nature in 2004. Instead, the skull is most likely that of a small-bodied modern human who suffered from a genetic condition known as microcephaly, which is characterized by a small head.

"It's no accident that this supposedly new species of hominid was dubbed the 'Hobbit;'" said Robert R. Martin, PhD, Curator of Biological Anthropology at the Field Museum and lead author of the paper. "It is simply fanciful to imagine that this fossil represents anything other than a modern human." The new study is the most wide-ranging, multidisciplinary assessment of the problems associated with the interpretation of the 18,000-year-old Flores hominid yet to be published. The authors include experts on:

  • scaling effects of body size, notably with respect to the brain: Dr. Martin and Ann M. MacLarnon, PhD, School of Human & Life Sciences, Roehampton University in London;
  • clinical and genetic aspects of human microcephaly: William B. Dobyns, PhD, Department of Human Genetics, University of Chicago; and
  • stone tools: James Phillips, PhD, Departments of Anthropology at the University of Illinois at Chicago and the Field Museum.

Skull cast and cast of the endocranial cavity (endocast) from a 32-year
old woman who had the body size of a 12-year-old child.
This is just one of four separate research teams that have recently published evidence indicating concluding that the Flores hominid is far more likely to be a small-bodied modern human suffering from a microcephaly than a new species derived from Homo erectus, as was claimed in the original Nature paper.

Significantly, the second most recent publication to conclude that the "Hobbit" was microcephalic--another multidimensional study that was published in the September 5, 2006, issue of Proceedings of the National Academy of Sciences--includes a co-author who was also a co-author of the original publication in Nature. That scientist, R.P. Soejono of the National Archaeological Research Center in Jakarta, Indonesia, now writes that the Flores hominid was microcephalic rather than a new hominid species.

Rewriting science
The starting point for the new research in Anatomical Record was the realization that the brain of the Flores skull (at 400 cc, the size of a grapefruit and less than one-third of the normal size for a modern human) is simply too small to fit anything previously known about human brain evolution. In addition, the stone tools found at the same site include types of tools that have only been reported for our own species, Homo sapiens.

Brain size of the Flores hominid, originally called Homo floresiensis, is known only from the main specimen discovered there, the LB1 skeleton. Skeletal fragments have been attributed to eight other individuals, but nothing can be said about their brain sizes. (They are small-bodied, but that has never been at issue.)

The new exhaustive research shows that the LB1 brain is simply too small to have been derived from H. erectus by evolutionary dwarfing, as was claimed by those who discovered it. In fact, the size of the brain corresponds very closely to the average value for modern human microcephalics. Microcephaly is a term that covers many conditions. There are more than 400 different human genes for which mutations can result in small brain size. Accordingly, there is a correspondingly wide range of different syndromes that are recognized in clinical practice. Many syndromes involve pronounced deficits ("low-functioning microcephaly"), but some have milder effects ("high-functioning microcephaly"), permitting survival into adulthood and a surprising degree of behavioral competence in certain cases. Microcephaly is often associated with severely reduced stature, but some microcephalics have relatively normal body size.

Because the LB1 skeleton is clearly that of an adult, it should obviously be compared with "high-functioning" modern human microcephalics rather than with "low-functioning" microcephalics who died early. The new study shows that skulls and brain casts from two modern human microcephalics who survived into adulthood are actually quite similar to those of the LB1 specimen. This supports the likelihood that LB1 was microcephalic.

Also, it has been claimed that LB1 had unusually large teeth ("megadonty"). However, it turns out that the teeth are not particularly large, after allowing for the expected effect of dwarfing. They are actually closely similar in size to those of a modern human microcephalic.

Another area of controversy concerns the stone tools discovered in association with the Flores fossils. Initially, the discoverers claimed that the tools were sophisticated, as indeed they are. More recently, continuity has been claimed with tools from Mata Menge on Flores that are purportedly 800,000 years ago. This is simply implausible, according to the authors of the new research.

"Nobody has even claimed cultural continuity in stone tool technology over such a long period (800,000 to 18,000 years ago)," Dr. Phillips said. "To do so ignores the significance of tools found with the LB1 skeleton that were made with the advanced prepared-core technique, otherwise confined to Neanderthals and modern humans."

There has been too much media hype and not enough sound scientific evaluation surrounding this discovery, Dr. Martin concluded. "Science needs more balance and less acrimony as we continue to unravel this discovery." Source : Field Museum

October 9, 2006 01:45 PMBiology

Biology News Net
RSS 2.0 Feed