Coca leaves contain a range of chemical compounds known as alkaloids. In modern times, the most notable among them is cocaine, extracted and purified by complex chemical means.
But the chewing of coca leaves for medicinal purposes has long been known to be a pastime at least as old as the Inca civilisation.
Other alkaloids within the leaves have mildly stimulating effects, can reduce hunger and aid digestion, and can mitigate the effects of high-altitude, low-oxygen environments.
Evidence of the chewing of the leaves has been found from around 3,000 years ago, but the addition of calcium-rich substances – which draw out far more of the alkaloids – was seen to be a much more recent development.
Now, Tom Dillehay of Vanderbilt University in the US and his colleagues have found evidence both of chewed leaves and calcium-rich rocks that were burned and scraped to supply ash for chewing.
The modern coca plant has ancestors with the same chemical properties
The evidence was found beneath the buried floors of the homes of foraging peoples from northwestern Peru, where the conditions were favourable to preserve what is normally a fleeting, organic remnant of a bygone civilisation.