I was going to post a comment here saying, "Aha! It was not an astrophysicist, or Bertrand Russel (as Hawking claimed), but rather William James with whom the story originated!" I went looking for a good source... and discovered I was wrong. What a fascinating little urban legend. Apparently, the aphorism goes way back, as does the tissue of myths and legends surrounding it. Misattributions all the way down!

I know wikipedia articles are (justly) frowned upon here, but the article on this phrase does seem to have links and citations to all the useful texts.

This is probably not quite what you're looking for, but I do know some pagan Iroquois. They wouldn't consider the turtle to be literal, but they do practice much of the old beliefs.