[feliyur]

Humans have historically had much to fear from furry things with large teeth, so don't need to resort to questionable theories.

The word "Orc" itself used to refer to Norse invaders, who did much of the same stuff "real" orcs do and unfortunately more (which is also directly related to what is now called xenophobia, or intolerance to foreigners and their culture).

So a strange-looking humanoid with traits of a predatory animal is a natural monster.