Sunday, May 17, 2009

Two new papers support Homo floresiensis as new species

Two new research paper published by Nature last week support the evidence that the so-called Indonesian “hobbit” skeletons belong to a separate human species. Homo floresiensis arrived on the island of Flores in the Lesser Sunda Islands a million years ago and lasted until they were probably wiped out by a volcano 10,000 years ago. Scientists have been unable to agree on the characterisation of the hobbit because although its brain is tiny, it has developed complex tools. The two new papers corroborate evidence to suggest they are a new species and not modern humans with abnormally small brains.

The first Nature paper says the feet of recently discovered miniature hominins found on Flores have a combination of human and more primitive features. An analysis of a Homo floresiensis fossil shows the dwarf-like creature walked in a different way from modern humans. The research does not take a definitive position on whether h. floresiensis is a new species or not. However the shape of the foot’s navicular bone similar to those of great apes, which means that they lacked an arch and were not efficient long-term runners. "Arches are the hallmark of a modern human foot," says William Harcourt-Smith, one of the paper’s authors. "This is another strong piece of the evidence that the 'hobbit' was not like us."

The research backs up similar findings about the fossil’s skull announced in January. The skull’s uneven shape was compared to modern humans and apes, as well as the fossil brain cases of early human ancestors. Karen Baab, a biological anthropologist at Stony Brook University in New York State said the unevenness was due to fossilisation. "The shape of the skull is consistent with what we would expect for a small archaic Homo," she said.

However, some scientists remain sceptical about the controversial find. Robert Eckhardt is a professor of developmental genetics and evolutionary morphology in the kinesiology department at Pennsylvania State University and co-author of a 2006 paper which concluded the shape of the skull represented “developmental abnormality." Eckhardt’s concern is the fossil’s tiny brain. "If it was three million years old, it wouldn't be a problem,” he said. “The problem is it is only 18,000 years old and it sticks out like a sore thumb."

A thumb is an accurate simile for the one meter tall Homo floresiensis. The first fossil was discovered at Liang Bua cave on the Indonesian island of Flores in 2003. It had human-like teeth with a receding forehead and no chin. The fossil was deemed to be somewhere between 38,000 and 18,000 years old. Archaeological evidence in the area found more bones from other individuals dating from 95,000 and 13,000 years ago. The first (and most complete) find was fully bipedal with a very small brain size of 417cc. It is this last statistic that causes most angst in scientific circles. It is similar to chimpanzees but only about one third the size of modern human brains.

But the second paper in last week’s “Nature” may have an answer to that puzzle too. An American Museum of Natural History study showed that dwarf mammals that live on islands evolved much smaller brains in relation to their body size than those on continental landmasses. The study looked at extinct pygmy hippos that lived on Madagascar and found their brain mass was 30 percent less than similar species on mainland Africa. Natural History Museum palaeontologist, Dr Eleanor Weston, says it may be advantageous to have smaller brains on isolated islands. “The brain is a costly organ that uses a lot of energy,” she said. "Whatever the explanation for the tiny brain of floresiensis relative to its body size, it’s likely that the fact that it lived on an island played a significant part in its evolution.”

It was long believed that no humans arrived on the isolated island of Flores until relative recent times (about 11,000 years ago) when homo sapiens arrived on boats. However in the 1960s a priest and part-time archaeologist Theodor Verhoeven found signs of a much earlier human presence. In the Soa Basin he found stone artefacts near stegodont (elephant ancestors) fossils, he said were around 750,000 years old. In the 1990s his claims were backed up when tools were dated and found to be 840,000 years old.

But no-one could find remains of actual humans until the first hobbit was found in Liang Bua which means "cool cave" in the local Manggarai language. The finders took the bones back to Jakarta where Peter Brown, a paleoanthropologist from Armidale’s University of New England, supervised cleaning, conservation, and analysis. The pelvic structure told him the bones were from a female. Brown soon realised he was dealing with an entirely new human species: Homo floresiensis. "To find that as recently as perhaps 13,000 years ago, there was another upright, bipedal…creature walking the planet at the same time as modern humans is as exciting as it was unexpected," he said. This find will keep on giving to science for many years to come. The challenge will now to find out how widespread the hobbits were and whether they came into contact with homo sapiens.

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