Source?

“Never doubt that a small group of thoughtful, committed citizens can change the world; indeed, it’s the only thing that ever has”: on NPR this morning, I heard this statement attributed to Rachel Carson. Wait a minute, said I. Isn’t that from Margaret Mead?

Possibly. The statement does not appear in the most recent editions (2002, 2012) of Bartlett’s Familiar Quotations. Quote Investigator finds “no substantive support for competing ascriptions” and tentatively ascribes it to Mead.