Posted by ESC on May 12, 2000
In Reply to: Derrivation posted by Sharyn Finnegan on May 12, 2000
: "Well I'll be a monkey's uncle"
The Random House Historical Dictionary of American Slang, Volume 2, H-O by J.E. Lighter has "monkey's uncle - n. (used in mild oaths and expressions of surprise). 1926 Maines & Grant 'Wise-Crack Dict.' Be a monkey's uncle. Be surprised..."
I am guessing that the expression started in connection with an incorrect interpretation that Darwin's theory of evolution states that man is descended from monkeys. (Rather than man and monkey had a common ancestor.)