The earliest origins of that one Margaret Mead quote

Margaret Mead’s quote about how a small group of citizens can change the world can be found all over the Internet. But did she actually say it? And where? The quote is notoriously hard to track down. I’ve tried googling around through And Keep Your Powder Dry and other likely locations but haven’t had much luck locating the origin of this quote. Then something I read — alas, I forget what — pointed me to a book with the quote in it: Earth At Omega: Passage to Planetization by Donald Keys. The book appeared in 1982, but obviously with a title like the thought is pre-Reagan.

At any rate the quote appears on page 79, at the opening of chapter six. I wonder whether it was something she said at a conference, or often said in conversation? Here’s a screenshot of the quote. I wonder if we can push it back even later in time and find an earlier occurrence?