In March of 1999, a man reported a strange occurrence in northern California. He was driving up Interstate 5 to visit friends in Oregon, and around 10:00 p.m., he took an exit off the highway to see if he could find a place to get some dinner. When he couldn't find a restaurant, he decided to pull onto the side of the road and make do with some snacks he had in the car. After he ate, he dozed off, and was soon awakened by a loud thump. When he got out to investigate, he found a good-sized rock on the hood of his car. He got back behind the wheel, started the car up and turned on the headlights. In the beams, he saw an 8-foot-tall creature covered in thick, dark hair. The creature watched him for a minute, turned in the road and walked slowly off into the woods.

Artist's rendition of what a bigfoot might look like, based on descriptions from eyewitnesses

People have been telling stories like this one for hundreds of years -- this creature was part of Native American folklore long before Europeans arrived on the continent. In the past 50 years alone, there have been thousands of reported bigfoot sightings in the United States and Canada, and many people claim to have seen a similar creature in the Himalayas. But in all this time, with all of these alleged encounters, nobody has unearthed bones or other conclusive proof of the giant primate. This has led many zoologists to dismiss the stories as hoaxes, hallucinations and misidentifications.

In this edition of HowStuffWorks, we'll examine the reports of bigfoot, also known as sasquatch, and its Asian cousin the yeti, to find out what these creatures might be and where they might come from. We'll also look at the compelling evidence for and against their existence and find out why so many people believe in them.