The tiny ancient humans dubbed hobbits, whose remains were discovered on an Indonesian island in 2003, were a previously unknown species altogether, according to two new studies.
Debate has raged in the scientific community since the fossils were found on the island of Flores, with some experts insisting they were descended from Homo erectus and others saying evolution could not account for their small brains.
About a metre (three feet) tall and weighing 30 kilos (65 pounds), the tiny, tool-making hunters may have roamed the remote island as recently as 8,000 years ago. Their fossils are about 18,000 years old.
Many scientists have said Homo floresiensis, as the creature is now formally known, was a prehistoric human stunted by natural selection over millennia through a process called insular dwarfing.
Others countered that even this evolutionary shrinking, well documented in island-bound animals, could not account for the chimpanzee-sized brain -- just a third the size of that in a modern human being.
The only plausible explanation, they insisted, was that the handful of specimens found had a genetic disorder resulting in an abnormally small skull or that they suffered from "dwarf cretinism" caused by deficient thyroids.
Two new studies in the British journal Nature go a long way toward settling the debate.
A team led by William Jungers of Stony Brook University in New York tackled the problem by analysing the hobbit's foot.
In some ways it is very human. The big toe is aligned with the others and the joints make it possible to extend the toes as the body's full weight falls on the foot -- attributes not found in great apes.
But in other respects it is startlingly primitive: far longer than its modern human equivalent and equipped with a very small big toe, long and curved lateral toes, and a weight-bearing structure closer to a chimpanzee's.
Recent archaeological evidence from Kenya shows that the modern foot evolved more than 1.5 million years ago, most likely in Homo erectus.
So unless the Flores hobbits became more primitive over time -- considered extremely unlikely -- they must have branched off the human line at an even earlier date.
For Jungers and colleagues, this suggests their ancestor was not Homo erectus "but instead some other more primitive hominin whose dispersal into southeast Asia is still undocumented."
Companion studies published by the Journal of Human Evolution bolster this theory and conjecture that these more ancient forebears may be the still poorly understood Homo habilis.
In any case, Homo floresiensis would be confirmed as a separate species.
But what still has not been explained the hobbit's inordinately small brain.
That's where hippos come into the picture.
Eleanor Weston and Adrian Lister of the Natural History Museum in London compared fossils of several species of ancient hippos found on the island of Madagascar with the mainland ancestors from which they had evolved.
They were surprised to find that insular dwarfing -- driven by the need to adapt to an island environment -- shrank their brains far more than had previously been thought possible.
"Whatever the explanation for the tiny brain of H. floresiensis relative to its body size, our evidence suggests that insular dwarfing could have played a role in its evolution," they conclude.
While the new studies answer some questions, they also raise new ones sure to spark fresh debate, Harvard professor Daniel Lieberman said in Nature.
Only more fossil evidence will indicate whether the hobbits of Flores evolved from Homo erectus, whose traces have been found throughout Eurasia, or from an even more ancient lineage not yet found outside Africa, he said.
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