Chocolate is made from the seeds of the cacao, an evergreen tropical shrub and member of the mallow family, related to hibiscus, okra, cotton and the notorious durian fruit (the smell of which was once described by Anthony Burgess as ''like eating raspberry blancmange on the lavatory’’). A mature cacao tree only produces 30 fruit pods a year, and once their seeds (which we confusingly call beans) are scraped out and dried the yield is less than a kilogram of beans per tree per annum. They are also tricky to grow, with a low pollination rate. Scientists still can’t agree which insects are doing the pollinating: most suspect tropical midges, but ants and aphids may also play a role. Honeybees definitely don’t like chocolate: the flowers are odourless and produce no nectar.  The chocolate tree’s scientific name, Theobroma cacao, comes from theobroma, or ''food of the gods’’ in Greek and cacao from the Olmec word kakawa. The Olmec were the prehistoric inhabitants of Mexico and probably the first consumers of chocolate. The oldest trace of cacao found was in an Olmec jug dating to 600BC, excavated near Colha in Belize. The Mayans who followed them called the drink cacahuatl (''atl’’ means water). They liked their chocolate hot and frothy, flavoured with chilli and vanilla, sculpting tubes into their pots so they could blow the liquid into a foam. The Aztecs also went for foam, but preferred theirs served cold. They also used the beans as currency: a rabbit was worth 10 beans; a slave, 100 beans. The standard weight measure was a carga, which was the total weight of cocoa beans a healthy person could carry (24,000 on a good day). Chocolate was the ultimate man’s drink, drunk by warriors to stimulate aggression and sexual performance and sacrificial victims just before they had their chests cut open and their still-beating hearts pulled out. Conquered peoples had to pay the Aztecs tribute in beans.  The arrival of the conquistadors introduced an important new ingredient: cane sugar from the Caribbean. This sweetened the bitter drink of the Aztecs called xocolatl (xoco pronounced ''choco’’ and meaning ''bitter’’). The result became so popular among the Spanish invaders that when the Bishop of Chiapas banned the drinking of it during church services his congregation poisoned him – with a laced cup of xocolatl. When Hernán Cortés took the beans and the foaming equipment back to Spain in 1527 he kick-started a European love affair with chocolate that shows no signs of abating. Previously the black ''almonds’’ had baffled Europeans (including Columbus) – one pirate raid on an Aztec ship had assumed they were rabbit droppings and threw the precious cargo overboard.  Is chocolate good for you?  The early uses for chocolate were medicinal and in recent years bold claims have been made for its therapeutic benefits. Chocolate contains serotonin, phenylethylamine (the so-called ''love chemical’’) and endorphins which, it is claimed, can relieve pain, reduce stress and reduce the risk of heart disease and cancer. Unfortunately, the beneficial chemicals come wrapped in a thick coating of sugar and (often) dairy fat, the negative effects of which more than outweigh the chemical upside. Interestingly, in blind tests where chocolate lovers were given cacao capsules (containing the same balance of chemicals) they didn’t report any of the same psychological benefits they had experienced when allowed to eat a bar of their favourite chocolate. This suggests that the positive effects come from having satisfied a craving; like other sweet and fatty foods, chocolate is habit forming. And yet, so powerful are the pleasure centres in our brain, that sucking on a piece can make your heart beat faster and for longer than a passionate kiss.  Chocolate is definitely bad news in quantity. It contains high levels of theobromine, a powerful stimulant of the central nervous system. Theobromine poisoning can cause heart failure, seizures, acute kidney damage and dehydration. A lethal dosage of chocolate for a human being is about 22lb (or 40 bars of Dairy Milk). On the other hand, one Smartie would be enough to kill a robin or a blackbird.
A quietly intriguing column from the brains behind QI, the BBC quiz show. This   week: QI unwraps chocolate