The most popular theory is that Sasquatch is a remnant population of Gigantopithicus, a Sasquatch-like hominid for which fossil evidence has been found in Asia.  The Gigantos probably came over to North America from Asia on the Bering land bridge along with modern humans.  In order to avoid competition with humans, they likely became nocturnal and avoided humans by living in high mountains, deep forest, and swamps. I live in Washington state and I can tell you that you can drive for hours looking at a horizon of trees and not see evidence of human habitation.<p>You can go to BFRO.net and read for yourself the thousands of eyewitness sightings by park rangers, law enforcement, military, biologists, and others of Sasquatch. They also have photos, videos, and an FAQ that deals with a lot of the common questions like why no body has been found. This is a perfect topic for Hacker News since mainstream science is not interested in an unclassified species, so individuals (hackers) have taken it upon themselves to do the science with the means they have available.