To readers of the New Yorker the story, "Vengeance is Ours," published on April 21 last year, seemed like a classic our-man-in-the-wilderness - in this case Papua New Guinea - dispatch. Written by Dr Jared Diamond, it examined a violent inter-clan blood feud in the highlands.

But a year later, the "Annals of Anthropology" piece has morphed into a nightmare legal challenge for both Diamond and the New Yorker, after two tribesmen mentioned in the story, Henep Isum and Daniel Wemp, filed suit in a New York court last week, seeking US$10 million ($17.6 million) and possible punitive damages for what they allege is defamation.

The lawsuit alleges the article "falsely accused plaintiffs ... of serious criminal activity and intentional and negligent infliction of emotional distress, including murder".

It is the sort of claim that makes journalists blanch.

The story has been taken off the New Yorker's website, although it is still available to subscribers.

A report, "Jared Diamond's Factual Collapse," posted on the self-appointed media-watcher website, claims the New Yorker story is inaccurate, that the magazine failed to contact indigenous people painted as "unrepentant killers, rapists and thieves," and may have endangered Wemp's life.

The bombshell, which also highlights the challenge posed by new media to traditional gatekeepers, is enough to cause a collective gasp around Times Square, where the New Yorker, arguably the world's most prestigious weekly, is based.

While the suit is embarrassing for the magazine - whose fact-checkers are revered as an industry standard - it could demolish the academic reputation of Diamond, the Pulitzer Prize-winning author of Guns, Germs and Steel and Collapse: How Societies Choose to Fail or Succeed.

Diamond starts his piece by describing how a 1992 clan battle in the PNG highlands, which killed Wemp's "beloved paternal uncle Soll", precipitated a three-year revenge cycle that killed 29 people, plus "the sacrifice of 300 pigs" before "Daniel succeeded in discharging his responsibility" and exacted revenge.

Wemp, a member of the Handa clan, allegedly sought revenge from Henep Isum who belonged to a rival clan, the Ombals.

The identity of Soll's killer was kept secret but Isum was the "owner of the fight", directing the fight for the Ombal clan. Under highland code Wemp would have to kill Isum.

After a skirmish, in which Diamond says Wemp was wounded by a spear, Wemp allegedly hired "over 200 men as allies." Eventually, an arrow is supposed to have cut Isum's spinal cord.

"He's still alive today, 11 years later, paralysed in a wheelchair, and maybe he'll live for another 11 years," Wemp is quoted as saying. He says that sometimes he shakes Isum's hand and expresses sorrow.

Diamond says he heard this tale six years later, in 2001-2002, when Wemp, then an employee of ChevronTexaco, drove the anthropologist around the highlands on a field study.

Wemp's revenge tale got Diamond musing that vengeance "may not be so far from our own habits of mind as we might like to think", a hypothesis explored in his article.

"While acting on vengeful feelings clearly needs to be discouraged,"

Diamond concludes, "acknowledging them should be not merely permitted but encouraged."

Given that he is caught up in the US revenge cycle - litigation - this seems ironically prophetic.

The stinkyjournalism website was founded by Rhonda Shearer, who runs a science research lab in New York.

It claims to have looked into the article, to the lengths of sending three fact-checkers to the highlands of New Guinea to interview the central characters.

The widow of Stephen Jay Gould, the esteemed biologist and palaeontologist who wrote best-selling science books, Shearer describes herself as a "Marcel Duchamp historian and artist" and is the director of the New York-based Art Science Research Laboratory.

The stinkyjournalism report is scathing. It claims the New Yorker's fact-checkers never contacted tribesmen named by Diamond and that "dozens of tribal members and police officials deny Diamond's entire tale about the bloody Ombal and Handa war, calling it 'untrue'." It cites linguistic analysis that quotations attributed to Wemp are "fabrications". It also picks up inaccuracies; thus Isum is not an Ombal but a Henep [in PNG the first name identifies one's clan].

Perhaps most damningly the website posted photographs of a tall, bearded man, identified as Isum.

Not a wheelchair in sight. Could the New Yorker be wrong?

Well, yes, says Shearer. She is no stranger to journalistic exposes. Her scoops include her 2007 revelation that a so-called "Monster Pig," 477kgs of wild pork that became a US media sensation, was a far smaller domestic animal, killed in a fake hunt.

As for her interest in Diamond's tale about internecine clan warfare in PNG, it all started with a komodo dragon.

"The stinky journalism website investigates different articles that strike us as dubious," she says. "In this case it was a coincidence. I was investigating an article that ran in the Australian and Pacific Island newspapers, where the government of PNG accused local newspapers of perpetuating a hoax about a komodo dragon running around and scaring villagers. There was no explanation about the accusation. But there was evidence. Like a footprint."

"Of the dragon?"

"Of the alleged dragon."

Long story short, the footprints were made by a cassowary. By then, Shearer had seen Diamond's piece [she tells me that according to his agent it was the most trafficked piece on the Boing Boing website] and sensed another scoop that would have far greater impact in New York and Los Angeles.

Her initial response on reading Diamond's piece was, "how do you keep someone with likely not the best medical care alive as a paraplegic in a wheelchair in that area? We can't keep Superman [Christopher Reeve] alive in New Jersey with millions of dollars? ... It just didn't make sense."

Efforts to contact Diamond and the New Yorker failed. Eventually, the magazine replied, "We stand by our story. No details are necessary."

It was a red flag to a bull.

Shearer was also uneasy that Wemp is the only cited source for Diamond's story, and that, while published in 2008, it was based on conversations from 2001-2002. Last July she emailed a statement from Wemp, who said he had no idea Diamond was writing a New Yorker article, to the magazine. Finally, she hired local scholars and journalists and asked them to visit the bush to try to verify Diamond's story.

Shearer says the New Yorker did confirm that Diamond spoke to Wemp again in May 2006 and backdated his notes, supposedly taken in 2001-2002. She sees this as deceptive and says Diamond reconstructed events.

Why, hadn't the New Yorker contacted Isum and Wemp?

Given the magazine's vaunted fact-checkers, this is a good question [her website says they finally spoke with Wemp in August 2008]. She had no problem doing so and was happy to supply telephone numbers.

Besides, she says, they could have contacted Wemp through the local World Wildlife Fund office, which supplies drivers like Wemp to Diamond.

But the axe falls heaviest on Jared Diamond, who enjoys an international reputation as a best-selling author. The stinkyjournalism postings allege Diamond was fast and loose with the facts, jumbling information to create a composite, or even inventing material.

Thus, far from Wemp apologising to Isum, the men say they never met.

The website quotes Committee of Concerned Journalists founder Bill Kovach who, damningly, describes Diamond's piece as "a complicated and in many ways confusing narrative based on what appears to be casual fragments of conversations" around which are "woven assertions".

It is not the first time a famous anthropologist has come under hostile fire. Margaret Mead - whose 1928 magnum opus Coming of Age in Samoa scandalised Americans by claiming Samoan girls were sexually active before marriage - was accused by New Zealand anthropologist Derek Freeman of being fooled by locals, who told her what she wanted to hear.

But if stinkyjournalism is correct, Diamond does not appear to have been hoodwinked by his subjects, but to have succumbed to that old journalistic temptation of not letting the facts stand in the way of a good story, even if, by using Wemp's name, he allegedly put him at risk.

When I rang the New Yorker to solicit their response to the allegations, the magazine was, perhaps understandingly in the litigious circumstances, reticent.

"Nothing's changed since last week for us," Alexa Cassa, the magazine's PR director told me. "So we don't really have any comment other than to say we stand by our story."

Anything else was off the record. I rang Diamond, a professor of geography at the University of California at Los Angeles, and left a message. He hasn't called back.

Shearer has plenty to say and her website promises a $40,000 rebuttal, a hefty response even by the standards of the New Yorker - no slouch when it comes to lengthy stories. But why had this story riled her so?

"The truth is unambiguously beautiful," she told me. While she concedes tight deadlines and fast-breaking stories can lead to errors, she holds publications like the New Yorker, where stories are fact-checked and time is lavished on editing, to a higher standard. Like peer-reviewed science papers, "the commitment to truth should be the same".

Does she think the New Yorker betrayed its values? "I think the facts speak for themselves."

Shearer's withering investigation of the New Yorker's methodology - including tracing people whom fact-checkers did call - shows news media can act as ethical watchdogs.

The story also highlights possible double standards: Diamond won critical acclaim yet refused to respond to Wemp's request to "sort out this problem" as the New Yorker piece "is very sensitive in my area". It will probably be an ongoing story.