According to Joshua Foer, writing in The New Yorker,
Among the Wakashan Indians of the Pacific Northwest, a grammatically correct sentence can't be formed without providing what linguists refer to as "evidentiality," inflecting the verb to indicate whether you are speaking from direct experience, inference, conjecture, or hearsay.Sounds like a language made for genealogists . . .
Joshua Foer, "Utopian for Beginners," The New Yorker, 24 December 2012, pp. 86-97 (quote p. 89).
Harold Henderson, "The Language for NGSQ!," Midwestern Microhistory: A Genealogy Blog, posted 8 January 2013 (http://midwesternmicrohistory.blogspot.com : accessed [access date]). [Please feel free to link to the specific post if you prefer.]