Where does ‘knocked up’ come from?

Anthony Horowitz (Diary, 4 February) tells us he was advised by a ‘sensitivity reader’ to remove the word scalpel from a book with a Native American character lest it suggest scalps (though the words are unrelated).

I’ve stumbled across the birth of a new forbidden phrase on Twitter, that social media swamp for the older swampster: knocked up. A California lawyer called Johnathan Perk declares in a tweet: ‘The phrase “knocked up”, referring to pregnancy, originated with US slavery. The Oxford English Dictionary traces the expression back to 1813. Back then the price of enslaved African women was “knocked up” by the auctioneer when she was pregnant – promoted as a deal for buyers.’ Even the evidence he produces shows this is not the case, but his tweet has been ‘liked’ 28,000 times. Now hundreds of people believe this story and many will think those who deny it are ‘slavery apologists’.

The example from 1813 cited in the OED has no reference to slavery. One from 1836 says: ‘N— women are knocked down by the auctioneer, and knocked up by the purchaser.’ (The word beginning with N is given in full.) The unpleasant play on words comes from a book attributed to David Crockett, Col Crockett’s Exploits and Adventures in Texas, published five years after his death. It was not Crockett’s own remark but one made by a thimblerigger (a swindler using three thimbles and a pea) whom the Colonel had asked to describe Natchez, Mississippi. Crockett himself had just proposed a toast, ‘The abolition of slavery’.

Knocked up here means ‘subjected to sexual intercourse’ or ‘made pregnant’. Mr Perk seems not to understand knocked down here – in use since the 18th century to mean ‘dispose of (an article) to a bidder at an auction sale by a knock with a hammer’.