Light at the Edge of the World. Wade Davis

No holy shrine in the land could be approached unless the supplicant had a quid of coca in his mouth. No field could be planted, no child brought into being, no elder released to the realm of the dead unless the transition was mediated with an offering of coca leaves for Pachamama, the Goddess of the Earth. To this day in parts of the Andes, distances are measured not in miles or kilometres but in coca chews. When Runa people meet, they do not shake hands, they exchange leaves. Soothsayers divine the future by interpreting the patterns of leaves cast onto cloth and the patterns in the venation of the leaves, a skill that can only be possessed by someone who has survived a lightning strike.

      In time, Tim would solve the botanical mystery, identify the point of origin of the domesticated species and reveal how they had diverged through centuries as their cultivation had spread over much of a continent. But perhaps his greatest research contribution came about from a simple nutritional analysis, the results of which horrified his government backers, even as they transformed scientific thinking about this most sacred of plants. Coca leaves do contain a small amount of cocaine, but only about as much as there is caffeine in a coffee bean. When the leaves are chewed, the drug is absorbed slowly through the mucous membrane of the mouth; it is a benign and useful stimulant in a harsh and unforgiving landscape. Highly effective as a treatment for altitude sickness, the leaves proved also to be extraordinarily nutritious. Rich in vitamins, coca has more calcium than any plant ever assayed by the U.S. Department of Agriculture, suggesting a vital role in a diet that traditionally lacked dairy products, especially for nursing mothers. It was also suggested that the plant enhances the ability of the body to digest carbohydrates at high elevation, again an ideal complement for a diet based on potatoes. In one elegant scientific assay, Tim revealed that coca was not a drug but a sacred food, a medicinal plant that had been used without any evidence of toxicity, let alone addiction, for over four thousand years by the peoples of the Andes. This revelation put into stark profile the draconian efforts underway then and continuing to this day to eradicate the traditional fields with herbicides that poison the myriad streams cascading out of the mountains to form the headwaters of the Rivers Amazon.

      COCA WAS THE lens through which the ancient rhythms and patterns of life in the Andes gradually came into focus. Wherever Tim and I travelled, we encountered evidence of worlds that had never been vanquished, indigenous communities that despite desperate struggles remained inextricably linked to their homelands. Nowhere was the spirit of survival stronger than among the Ika and Kogi, descendants of an ancient civilization that had flourished on the Caribbean plain of Colombia for five hundred years before the arrival of Europeans. Since the time of Columbus, these Indians have resisted invaders by retreating higher and higher into the inaccessible reaches of the Sierra Nevada de Santa Marta, the highest coastal mountain range on Earth. Ruled to this day by a ritual priesthood, they consider themselves the Elder Brothers. We, who to their minds have ruined much of the world, are deemed the Younger Brothers.

      Tim and I entered the mountains from the south, along a narrow track that rose in a day and a night through cactus and thorn scrub to a steep river draw carved into the rising flank of the massif. Just after dawn, having made our way through the shadowy darkness, past scattered houses of stone linked one to another by small fields of coca, leaves translucent in the early morning light, we came upon a portal to the sun. Framed within its arch was a solitary figure, a silhouette blocking entry to the upper valley of a river known to the Indians as the Donachuí.