It seems as if every few weeks there’s another watermelon controversy. The Boston Herald got in trouble for publishing a cartoon of the White House fence-jumper, having made his way into Obama’s bathroom, recommending watermelon-flavored toothpaste to the president. A high-school football coach in Charleston, South Carolina, was briefly fired for a bizarre post-game celebration ritual in which his team smashed a watermelon while making ape-like noises. While hosting the National Book Awards, author Daniel Handler (a.k.a. Lemony Snicket) joked about how his friend Jacqueline Woodson, who had won the young people’s literature award for her memoir Brown Girl Dreaming, was allergic to watermelon. And most recently, activists protesting the killing of Michael Brown were greeted with an ugly display while marching through Rosebud, Missouri, on their way from Ferguson to Jefferson City: malt liquor, fried chicken, a Confederate flag, and, of course, a watermelon.

While mainstream-media figures deride these instances of racism, or at least racial insensitivity, another conversation takes place on Twitter feeds and comment boards: What, many ask, does a watermelon have to do with race? What’s so offensive about liking watermelon? Don’t white people like watermelon too? Since these conversations tend to focus on the individual intent of the cartoonist, coach, or emcee, it’s all too easy to exculpate them from blame, since the racial meaning of the watermelon is so ambiguous.

But the stereotype that African Americans are excessively fond of watermelon emerged for a specific historical reason and served a specific political purpose. The trope came into full force when slaves won their emancipation during the Civil War. Free black people grew, ate, and sold watermelons, and in doing so made the fruit a symbol of their freedom. Southern whites, threatened by blacks’ newfound freedom, responded by making the fruit a symbol of black people’s perceived uncleanliness, laziness, childishness, and unwanted public presence. This racist trope then exploded in American popular culture, becoming so pervasive that its historical origin became obscure. Few Americans in 1900 would’ve guessed the stereotype was less than half a century old...