Smithsonian.com

Llamas can still be found at Machu Picchu today (image courtesy of flickr user Santiago S.V.)

The Incas dominated much of South America for centuries, building a vast empire that stretched high into the Andes where the terraced city of Machu Picchu still inspires wonder. Now scientists in France and Peru, reporting in the journal Antiquity, reveal what made it all possible: llama dung.

The researchers analyzed mud cores from the bottom of a lake near the Incan town of Ollantaytambo in Peru. These sediment samples contain a record of past environmental conditions in the area. (In some places, scientists have found cores that give records stretching back tens of thousands of years). In the Peruvian sample, the researchers found a sudden increase in maize (corn) pollen starting around 2,700 years ago. Unlike the wild-grown quinoa that the Incas had previously relied upon to survive, cultivated maize provided more energy and could be stored or transported long distances, perfect for fueling a growing empire. But how were they able to grow maize high up in the mountains?

The mud samples also provide that answer. About the same time that there was an increase in maize pollen, there was an increase in oribatid mites, tiny insects that live in soil and feed on feces. The researchers conclude that dung from llamas—which the Incas had domesticated hundreds of years previously—provided food for all those mites. Llamas “defecate communally so [their dung] is easily gathered,” Alex Chepstow-Lusty of the French Institute of Andean Studies explained to the Guardian. The Incans could then use the poop as fertilizer for their maize fields, which reached elevations up to 11,000 feet above sea level. “This widespread shift to agriculture and societal development was only possible with an extra ingredient—organic fertilizers on a vast scale,” Chepstow-Lusty says.