The call of nature
What's the meaning of the phrase 'The call of nature'?
Euphemism for the desire to urinate or defecate.
What's the origin of the phrase 'The call of nature'?
'The call of nature' is an ambiguous expression to choose to indicate the need to go to the lavatory. On the one hand it alludes to such an urge being natural and on the other it uses veiled language to cover it up.
Prior to its use as a euphemism 'call of nature' was used to describe our urge to enjoy the pleasures of rural tranquillity.
The euphemistic meaning was coined in the mid-18th century and begins appearing in print around that time. Here's an early example from Laurence Sterne's 1761 novel The Life and Opinions of Tristram Shandy, Gentleman:
Shew me a city so macerated with expectation - who neither eat, or drank, or slept, or prayed, or hearkened to the calls either of religion or nature, for seven-and-twenty days together, who could have held out one day longer.
Sterne's novel is famously obscure and difficult to interpret so, although 'call of nature' in the above appears to refer to urination it's possible that Sterne meant something else by it. There's no such doubt about this entry published in October 1852 in the Tailor & Cutter magazine:
The calls of Nature are permitted and Clerical Staff may use the garden below the second gate.