The Great Bone Hoax : UNRAVELING PILTDOWN: The Science Fraud of the Century and Its Solution.<i> By John Evangelist Walsh (Random House: $25, 270 pp.)</i>

In science we presume that an unsolved mystery will one day be unraveled because nature’s answers are sitting out there somewhere. In history, the answers are sitting back in time, and if they have been lost to the memory of their long-gone keepers (or covered up with a conspiracy), the mystery may be more than unsolved; it may be unsolvable. Who shot JFK? After decades of endless speculation, theorizing and conjecture, we are no closer to a final answer than we were in 1963.

What I have discovered in investigating mysteries for Skeptic magazine is that once a story takes on a life of its own, a satisfactory answer may be impossible simply because the mystery is more tantalizing than its solution.

In the history of science, there is one enduring mystery in this category of unsolvables: the Piltdown hoax, or what John Evangelist Walsh calls “the science fraud of the century” in his book, “Unraveling Piltdown: The Science Fraud of the Century and Its Solution.” Unfortunately, despite the author’s subtitle claim of “and Its Solution,” as with JFK, Walsh’s return to the lone perpetrator likely will be met with scorn by the Oliver Stones of Piltdown. The reason is simple: There is no smoking gun and the remaining speculative theories will continue being contested as long as imaginative people are interested.

What are they contesting and what is the mystery?

On Feb. 15, 1912, a British lawyer named Charles Dawson, who devoted every moment of his spare time to amateur archeology, presented to the renowned Keeper of Geology of the British Museum of Natural History, Arthur Smith Woodward, several cranial fragments that appeared to belong to an ancient hominid, or protohuman. Dawson told Smith Woodward that in 1908, workmen had unearthed the fragments from a gravel pit at Piltdown in Sussex, accidentally smashing them with their picks. The skull fragments were modern in appearance, yet they were found in deep, ancient layers, indicating great antiquity.

On June 2, 1912, Smith Woodward visited the pit with Dawson and a youthful Jesuit named Pierre Teilhard de Chardin, later to become the world-famous author of “The Phenomenon of Man,” the book that attempted a scientific proof of the spiritual nature of humanity. There, Dawson discovered the lower jaw of the skull, including two molars, which were very ape-like in structure but indicated human-like wear. Additional digs uncovered stone tools, chipped bones and fossil animal teeth that helped to place the ancient hominid well back in our evolutionary history.

Six months later, Dawson, under the auspices and endorsement of Smith Woodward, announced the great find to the Geological Society of London. A few skeptics voiced their doubts, but one of the crucial pieces of evidence that might have deflected their concerns--the jaw--was mysteriously broken in just the right places to preclude resolution. The following year Teilhard de Chardin found an ape-like lower canine tooth similar to the ones from the earlier discovery. In 1915, at another pit two miles from Piltdown, Dawson uncovered two more hominid skull fragments along with another tooth similar to those from the previous finds.

The scientific world was ecstatic. It was too good to be true: This new find had confirmed what they always assumed about human evolution--our large brain had lifted us above our simian ancestors. Now there could be no doubt.

Unfortunately, it was too good to be true. In 1953, scientists Kenneth Oakley, J. S. Weiner and W. E. le Gros Clark announced that new dating techniques had proved the skull fragments to be of modern origin, as was the orangutan jaw--all stained, chipped and filed to look ancient. The flint artifacts were worked with modern tools, the fossil animal teeth were from elsewhere and everything was carefully placed in the Piltdown pit. It was all a hoax--four decades’ worth.

Now the mystery begins. Who did it? Conspiracy theorists have produced an endless variety of combinations, most of which include Dawson as everything from patsy to accomplice to orchestrator. Walsh devotes a chapter to some 20 or so accused and additional chapters to the big-name conspirators, including Teilhard de Chardin, Oxford anatomist Sir Arthur Keith and even Sir Arthur Conan Doyle.

But Walsh dismisses them all. The case is now closed, he says. Dawson acted alone. His proof? Dawson had both the means and the motive: overweening ambition to make a name for himself in science and previous experience faking antiquities. Walsh carefully documents Dawson’s long history of questionable finds, including a Roman horseshoe (before there existed such a thing), an ancient boat with not-so-ancient timbers, some fraudulent British bricks from Roman times, plagiarism and more. Dawson had both the knowledge and the skill to hoax Piltdown all by himself. Plus, Walsh argues, there is no evidence beyond a reasonable doubt to convict anyone else and, to paraphrase the colorful language of another lawyer on a recent famous case, if the evidence doesn’t fit, you must acquit.

This is a fair and reasonable argument. If this were a court of law (especially in Los Angeles, considering its recent courtroom history), they would all walk. Walsh even dismisses Martin A. C. Hinton, a curator who worked for Smith Woodward at the British Museum and who was the subject of a May 23, 1996, paper in Nature magazine by King’s College paleontologist Brian Gardiner. Gardiner asserts that Hinton played the hoax for revenge against his boss, who apparently refused to pay his wages in a timely fashion.

Gardiner was given a trunk, found 20 years ago, allegedly belonging to Hinton, in which he found fossils, teeth and other remains similar to those found at Piltdown as well as a mixture of chemicals used in staining said items. “I was able to show that the stains in the teeth and the stains in the trunk were the same as those at Piltdown,” Gardiner said, also explaining that Hinton had done some staining for Dawson and planted the evidence for his dupe to take to his boss. Thus, Gardiner said, Dawson was a patsy, not a perpetrator. Walsh counters with references that the staining was done after the hoax was exposed in 1953 and that Hinton was only experimenting to see how Dawson did it.

Who faked Piltdown? Who knows? As it is with the Kennedy assassination, a lone perpetrator is a cleaner, simpler theory than a complex conspiracy, but conspiracies do happen in history, so we cannot dismiss them. Walsh builds an extremely strong case against Dawson, even though Gardiner claims that “Dawson was too ignorant--an old country solicitor” to carry off such a hoax. Lawyers may be many things, including the butt of jokes, but ignorant isn’t usually one of them.

The Piltdown mystery will not end with Walsh’s compelling work, but he has done a fine job of narrowing the field and acquitting those who are probably innocent. But as skeptics like to say, for those who believe, proof isn’t necessary; for those who do not believe, proof isn’t possible.