SingingGandalf:
if they are Gicantopithacus, they'd be an otherwise extinct species of giant ape; not our ancestor, but more similar to us than say, gorillas or orangutans.
That's actually the
opposite of the science:
Gigantopithecus, subfamily
Ponginae, is closely allied with
Sivapithecus and
Indopithecus, making them relatives of the orangutan,
closer in relationship to them than to us,
homo sapiens.
Gigantopithecus is also generally accepted to have moved quadruped style (bent over, supporting itself on all four limbs) from the evidence we have, not bipedal (standing upright and walking on just two limbs, as we, and supposedly the yeti, do), so that is another point against it as having anything to do with it.
FormulaFourteen:
Assuming that most sightings are claiming to see the "same things" is largely uninformed.
It's hard to take it any other way, I'd have thought, if I'm reading you right; to suggest that many people who sight yetis, for example, are all describing different things gives it less credibility, not more.
That is of course not to deny that that is how most of these legendary creatures come about.
However, scientific progress has been made through modern means, and Channel 4 here in the U.K. ran a fascinating short series last year, which traveled the world collecting eye-witness reports and (more importantly) samples for DNA analysis, from those who had hunted, tracked, or otherwise had sightings of yeti, migo, big-foot and what-have-you. The vast majority of these proved to be readily identifiable (and often hilariously inappropriate to the sort of encounter suggested - such as in one case, a cow).
Perhaps most interestingly the yeti came out in first place as a genuine "hidden" animal, although not a hominid. The DNA evidence connects it to a known, but thought to be extinct, ancient polar bear/ brown bear hybrid, which is right for the conditions.
You can read a report on the work done to identify the Yeti in this series
here.