Q From Michael Josett; Chuck Emery: I’ve always been curious where monkey’s uncle came from and what it means.
A What it means is nothing very profound. It’s just an exclamation of surprise: “Well, I’ll be a monkey’s uncle!”
It has been assumed to be a reference to Darwin’s Origin of Species of 1859, in which he argued the close evolutionary relationship between humans, apes and monkeys. You may recall the famous debate between “Soapy Sam” Wilberforce, the Bishop of Oxford, and Thomas Huxley, in which the bishop is said to have asked sarcastically whether “it was through Huxley’s grandfather or grandmother that Huxley claimed his descent from a monkey.”
A direct link with Darwin’s book would place the expression’s genesis later than 1859 and indeed most reference books suggest it dates from the 1920s, most probably accepting the first example in the Oxford English Dictionary, which is from an Ohio newspaper of 1925. It had become a catchphrase in the US earlier than that: an advertisement in the El Paso Herald on 31 July 1917 for the comedy play Brass Monkey at the Unique Theatre is headlined “Well, I’m a monkey’s uncle!”
But I suspect the origin is much earlier. This parody of Longfellow’s Song of Hiawatha appeared in James Parton’s compendium The Humorous Poetry of the English Language in 1856. It’s said to be from Punch:
Out came sundry comic Indians
Of the tribe of Kut-an-hack-um.
With the growling Downy Beaver,
With the valiant Monkey’s Uncle.
This may be just an accident of invention, but two British newspapers a decade earlier included reviews of a comic play, The Wigwam, which takes place in an Indian encampment in Canada.
Mr. Frank Matthews was all that a runaway “governor” could hope to be in savage life, with a plurality of wives; while Mr Oxberry was a veritable monkey’s uncle in his rage and jealousy.
The Morning Post, 26 Jan. 1847.
These two examples precede the publication of Darwin’s book, but the ideas behind evolution had been “in the air” before then. In any case, the idiom didn’t really need to be backed by ideas of evolution in order to be generated as a humorous cry.