Not give a monkey’s

The expression 'not give a monkey’s' as in a person saying or writing, 'I don't give a monkey's', is a more refined form of ' I don't give a damn' or ' fuck' about something or other, whatever it may be. The exact origin remains obscure but it is first attested from the early 20th century. It does seem, however, that something is missing here - a monkey’s what? The most likely candidates found on record are ‘uncle’, ‘arse’, ‘toss, and even 'left testicle’ but there are many others. In The Merchant of Venice Act III, Scene I, Shakespeare wrote, “I would not have given it for a wilderness of monkeys.” A wilderness of monkeys is certainly a step up in class from not giving a monkey's 'uncle' 'arse', 'toss' etc. but citing Shakespeare as the source is definitely a step too far. See also Monkey's uncle.