THE GIST

- DNA tests have not yet offered proof that Earhart lived as a castaway on a remote island in the Pacific.

- Genetic tests have not been able to answer whether a bone fragment is in fact part of a human finger.

- Researchers have, however, succeeded in extracting human DNA from clumps of a substance believed to be feces.

VIDEO: Amelia Earhart Search Continues

Scientific investigations have revealed that human DNA may be present in fragments of material which could provide crucial information about the fate of Amelia Earhart, the legendary pilot who disappeared 74 years ago while flying over the Pacific Ocean in a record attempt to circle the world at the equator.

Collected on Nikumaroro, an uninhabited, waterless tropical island in the southwestern Pacific republic of Kiribati where Earhart and navigator Fred Noonan might have made an emergency landing, the material consisted of a tiny bone fragment and clumps of material resembling soil or feces.

While human mitochondrial DNA was recovered from the clumps, tests on the bone fragment were less conclusive.

"There does appear to be ancient DNA present in the bones and material we collected but it's in very bad condition," Ric Gillespie, executive director of The International Group for Historic Aircraft Recovery (TIGHAR), which has long been investigating the Earhart mystery, told Discovery News.

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TIGHAR's investigations and theories challenge the assumption that Earhart's twin-engined Lockheed "Electra" crashed in the ocean when running out of fuel on July 2, 1937.

"A large and growing body of circumstantial evidence suggests that Earhart and her navigator landed and lived for a time as castaways only to eventually perish on the atoll," Gillespie said.

Discovered last June with several other artifacts during a month-long expedition, the bone fragment's features led forensic anthropologist Karen Burns to wonder if it might be part of a human finger.

Indeed, it was found at a site on the atoll where the partial skeleton of a castaway was discovered in 1940.

Recovered by British Colonial Service Officer Gerald Gallagher, the partial skeleton was described in a forensic report and attributed to an individual "more likely female than male," "more likely white than Polynesian or other Pacific Islander," "most likely between 5 feet 5 inches and 5 feet 9 inches in height."

Unfortunately the bones have been lost.

"No hand bones were found in 1940, so the presence of a surviving human finger bone seems plausible," Gillespie said.

This is one of the last photographs made in Los Angeles of Amelia Earhart with her navigator as they completed preparations for their ill-fated flight.Bettmann/CORBIS

Structurally finger-like, the bone fragment was initially attributed to a turtle. It was only when archaeologist Tom King catalogued the turtle bones found at the site that questions began to arise.

"All turtle bones were associated with the shell. No limb bones were identified. If whoever brought the turtle to the site didn't bring the legs, how did a phalanx-like bone get there?" said Gillespie.

In an attempt to solve the mystery, the bone fragment was sent to the Molecular Anthropology Laboratories at the University of Oklahoma in Norman, Okla.

Initial tests for the presence of human mitochondrial DNA in the bone fragment were positive, but subsequent testing was unable to replicate the results.

According to Cecil M. Lewis, who carried out the DNA tests, this suggests that either the initial detection of human DNA was attributed to a sporadic DNA contamination event, or there was human DNA in the extract, but it was too little, or of too poor quality for a consistent analysis.

Another possibility is that the DNA in the bone was non-human.

More general tests for animal DNA, human and non-human, provided "no positive results," suggesting three possibilities: there was no animal DNA in the bone; there was animal DNA, but it was too little or of too poor of quality to reliably analyze; or the real time Polymerase Chain Reaction method used to detect the DNA was ineffective for targeting the particular animal.

"For now, the question of whether the bone is human must remain unanswered," Lewis concluded.

The researchers decided to preserve a tiny fragment of the bone, hoping to use it in the future as less destructive, and more sensitive genomic methods develop.

Analysis of clumps of a substance recovered from the same site yielded more promising results.

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Archaeologically, the clumps are anomalous in the context of the site. Examined by University of Maine anthropologist Kristin Sobolik, the mass was found to possess some fecal properties.

The material has been analyzed by the Molecular Anthropology Laboratories at Oklahoma University. There, Lewis's team was able to extract human mitochondrial DNA.

"DNA from two individuals was detected but to date, the amount extracted is not sufficient for comparison to Earhart reference samples," Gillespie said.

According to Lewis, the most common explanation for multiple sequences is either the sample is associated with a temporary latrine used by more than one person, or the retrieved data still includes modern human contamination.

"We will continue to explore how well these explanations fit the data by further molecular testing," Lewis said.

In addition to the bacteria and human DNA analyses, future analysis will include targets for plants and animals.

According to Lewis, the presence of certain plant and animal DNA would be a further indication that the clumps are fecal matter and could provide information about the diet and general health of the individual.