THE origins of the diminutive ancient human cousin nicknamed the “hobbit” are again in question after scientists in the United States challenged the claim that it constitutes a completely new species.

The discovery on an Indonesian island of bones of an 18,000-year-old creature just over 3ft (1m) tall was hailed in 2004 as one of the most significant fossil finds for 150 years. Analysis of Homo floresiensis’s skeleton, and a reconstruction of the brain, suggested that it represented a new branch of humanity’s family tree, a dwarf that had evolved from our ancestor Homo erectus.

The fossils, from a specimen known as LB1 after the Liang Bua cave where it was found, have become the subject of fierce controversy, a minority of scientists arguing that it was a modern human who had microcephaly, a congenital disorder that stunts brain growth.

Research led by Robert Martin, curator of biological anthropology at the Field Museum in Chicago, has now added weight to this rival hypothesis. In a study published today in the journal Science, Dr Martin casts doubt on the reconstruction of LB1’s brain and argues that details of its anatomy are consistent only with a microcephalic Homo sapiens. The stone tools found are too sophisticated to have been made by anything other than modern humans, he also writes.

The study suggests that while dwarfing sometimes occurs among mammals confined to small islands, it does so in proportions that do not fit the hobbit. The brain is too small for this to have happened: for LB1 to be a dwarfed form of Homo erectus, it would have to have been no more than 1ft.

Dr Martin said: “The tiny cranial capacity of LB1, smaller than in any known hominid younger than three million years old, is far too small to have been derived from Homo erectus by normal dwarfing.”

He added that the reconstruction of LB1’s brain done last year by Dean Falk, of Florida State University, was based on a poor cast of the skull, and had been compared with a microcephalic ten-year-old instead of with an adult. “This defective plaster copy of a microcephalic skull used in the study by Falk et al is inappropriate for any scientific study, especially one dealing with a topic as demanding and high-profile as this,” he said.

“There has been too much media hype and too little critical scientific evaluation, and it is unacceptable that papers should be published without providing proper details of the specimens examined. The principle of replicability is fundamental to good science.”

Dr Falk rejected the criticisms, noting that Dr Martin had put forward only line-drawings of skulls that lacked the detail to support his case. Without such evidence, she wrote in Science, “the assertions of Martin et al remain unsubstantiated and difficult to address in further detail”.

Chris Stringer, of the Natural History Museum in London, said: “There are valid questions about the brain, but when you look at all the evidence together — the mandibles, the skeleton, the story of the site — the evidence is incredibly strong that this is an unusual and distinct kind of human.”

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