Linda Godfrey is so sure about the existence of weird walking wolves that she's written a book titled "Real Wolfmen: True Encounters in Modern America." In more than 300 pages, she lays out dozens of stories about sightings of nasty-looking beasts running around on their hairy hind legs. Scientists are unconvinced — but they do admit that humans are virtually hard-wired to watch out for wolves on the darkness.

"The werewolf idea is strictly a product of our imagination, but it comes along with a culture of thousands of years of fear of wolves," said Michigan Tech's Rolf Peterson, who has studied wolves for decades at Isle Royale National Park in Lake Superior. "It's just an outgrowth of that. But there's nothing out there that's anything like a werewolf. It's all in our heads."

Try telling that to Godfrey and the people whose dog-man reports are featured in her book.

"I've received hundreds of reports over the years ... and that's probably a small percentage of the actual sightings of these creatures," she told me. "So many people are in denial when they have these experiences, because it sort of rocks their world."

Quest for the beast
Godfrey had her own world rocked in 1991 when, as a rookie reporter in Elkhorn, Wis., she wrote about a sightings of a creature that came to be known as the "Beast of Bray Road." The beast was said to be a 6-foot-tall, fur-covered wolflike animal that chased after witnesses on its hind legs.

Linda Godfrey

Linda Godfrey, author of "Real Wolfmen," created this sketch of an upright canid based on reports from witnesses.

"I can't find any scientific reason why feral canines should walk on their hind legs, in the absence of, say, a missing forelimb," Godfrey said. "I can't find any experts who can tell me why they should do this. But they do."

Sure, there have been hoaxes: The most famous case is the Gable Film, a home-movie reel that appears to show a dark shape attacking the person holding the camera. The film was eventually traced to a couple of guys trying to hype a "Michigan Dog-Man" tale.

Godfrey acknowledges that some of the wolfman reports actually turn out to be misidentifications of four-legged wolves, or bears rearing up on their hind legs. Other "wolfmen" have turned out merely to be weird men lurking around the countryside. And there's actually a rare malady known as hypertrichosis that can make people look like the wolfmen in the movies.

But Godfrey insists that even after all those cases are eliminated, there are solid sightings that can't be explained away.

She emphasized that she's not making claims about magical beings that change from humans to wolves and back again, like Jacob and his fellow shape-shifters in the wildly popular "Twilight" saga. "The thing about these creatures that people report to me is that they're not describing something that has human characteristics, only odd behavior that reminds them of humans," Godfrey said.

So if there are all these reports of "upright canids," why haven't scientists identified this, um, unusual species? "It has the ability to get around whichever way is most convenient," Godfrey explained. "If you saw one of these things on four legs, you would just say there's an extremely large, creepy-looking canine that's walking by on all fours."

In her book, Godfrey voices the hope that high-tech gear such as motion-sensitive trail cameras and night-vision imaging devices will eventually produce indisputable evidence to back up all the stories Godfrey has heard over the past 20 years. But so far, scientists aren't buying it. "I haven't had any that say, 'Yes, I know there are dog-men,'" Godfrey acknowledged.

Rabies and other reasons
Michigan Tech's Peterson is one of the scientists Godfrey has contacted in the course of her wolfman quest — and although he doesn't see any reason to believe the dog-man reports are real, he notes that there are plenty of reasons for werewolf tales to take root.

"The basis for people's fear of wolves is not totally without evidence," he told me. "The wolf is the species that has posed the most difficulty for us, aside from our own species."

For one thing, there's rabies, a disease that was common in Europe during the heyday of the werewolf saga, starting in the 16th century. It would have been unnerving to see someone who was bitten by a rabid dog or wolf sicken and go mad within a matter of days — and that would have added credence to the idea that such people were being transformed into a kind of wild animal.

Another reason is that wolves truly are predators: In the old days, children who were pressed into service as shepherds made for tasty targets, Peterson noted. And we're not just talking about the old days. Peterson pointed to a grisly string of wolf attacks on children in India that took place in 1996-97, as well as more recent episodes.

There's another side of the coin, of course: Thousands of years ago, humans domesticated wolves to create man's best friend. "We've been around wolves for tens of thousands of years, and we developed dogs out of it, so we have a long association with that particular species," Peterson said. With that kind of complex love-hate relationship, it's not surprising that the world's cultures have produced such a rich store of wolf-man archetypes — ranging from the skinwalkers of Native American lore to Jacob's hunky wolf pack. Our tendency to see wolves in the shadowy shapes of the night may well be a reflex that's been fine-tuned over countless millennia.

But what about the wolves? Peterson's specialty is the study of relationships between wolves and their prey, and he's noticed that the wolves of Isle Royale periodically change their perspective on people as well.

"Seven, eight years ago, after 45 years of being totally terrified of people, the wolves suddenly lost their fear of people," he told me. "Then, after about three years, they switched back to being afraid. I have absolutely no idea what caused either switch. They have their own cultural knowledge about us, and they transmit that from generation to generation, I suspect."

Did I just feel a chill going down my spine?

More Halloween stories to chew on:

• 2002: Ghostly mysteries solved
• 2003: Why we seek out an eek
• 2004: Sharing your scares
• 2005: Ghosts on the rise
• 2006: Bring me your ghost stories!
• 2007: The science of spooks
• 2008: Chasing phantoms on film
• 2008: The science of bloodsuckers
• 2009: Seven ghoulish discoveries
• 2010: Spooky stuff from NASA
• 2010: How your brain handles terror scares
• 2011: Why the 'paranormal' is just normal
• 2012: Sleuth finds the truth behind ghost stories

Stay tuned for a Halloween reality check on vampire legends.

Alan Boyle is NBCNews.com's science editor. Connect with the Cosmic Log community by "liking" the log's Facebook page, following @b0yle on Twitter and adding the Cosmic Log page to your Google+ presence. To keep up with Cosmic Log as well as NBCNews.com's other stories about science and space, sign up for the Tech & Science newsletter, delivered to your email in-box every weekday. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for new worlds.