You may have heard that oysters are an aphrodisiac -- but what about potatoes, skink flesh, and sparrow brains? These things were once considered aphrodisiacs, too. Almost everything edible was, at one time or another.

Aphrodisiac recipes have been cooked up throughout the world for millennia. In Europe, up to the eighteenth century, many recipes were based on the theories of the Roman physician Galen, who wrote that foods worked as aphrodisiacs if they were "warm and moist" and also "windy," meaning they produced flatulence. Spices, mainly pepper, were important in aphrodisiac recipes. And because they were reckoned to have these qualities, carrots, asparagus, anise, mustard, nettles, and sweet peas were commonly considered aphrodisiacs.

An aphrodisiac, as we use the term today, is something that inspires lust. It usually isn't meant to cure impotence or infertility, problems that are now handled by separate fields of medicine. But until recently there was little distinction between sexual desire and function. Any lack of lust, potency, or fertility would have a common cure in an aphrodisiac. Galen thought that a "wind" -- or as one 16th-century writer put it, an "insensible pollution" -- inflated the penis to cause an erection, so anything that made you gassy would also make you erect.

Galen's theories were not the only basis for concocting aphrodisiacs. Mandrake root was eaten as an aphrodisiac and as a cure for female infertility because the forked root was supposed to resemble a woman's thighs. This was based on an arcane philosophy called the "doctrine of signatures." Oysters may have come to be known as an aphrodisiac only by their resemblance to female genitals. Few old medical texts listed oysters as an aphrodisiac, although literary allusions to that use are plentiful.

Parts of the skink, a kind of lizard, were thought to be an aphrodisiac for centuries. It's hard to say why exactly, but three different ancient authors make the claim. Potatoes, both sweet and white, were once known as an aphrodisiac in Europe, probably because they were a rare delicacy when they were first transplanted from the Americas.