There are instances in South America, North Africa, and Australia, where some prehistoric person took the foot of an animal such as a large bird or lizard, with feet that resemble human hands, and stenciled round it onto a wall. Is the repetition of this trope over wide distances just a freaky coincidence? Yes.

Well, there's probably something mimetic going on, like the idea of stenciling round your hand at all. "Neat! I'm gonna do that too! I'm gonna get my little brother to do it! And my chicken! And this leftover lizard foot!" Memes spread easily. Kilroy was here, nobody writes that one on walls any more, and hands were stenciled over thousands of years, but we have an evolving culture now.