DAN SALADINO

In the early 1980s, an American plant scientist called Howard-Yana Shapiro climbed thousands of metres to reach remote villages in the eastern highlands of the Mexican state of Oaxaca. The area is home to the Mixe people. No one knew when or how the Mixe had settled in the rugged mountains, and there is little archaeology to explain their history. The soldier and explorer Hernán Cortés, who had conquered the Aztecs, was thwarted by the Mixe. ‘Their land is so rocky that it cannot be crossed even on foot,’ he wrote in 1525, ‘for I have twice sent people to conquer them, who were unable to do so because of the roughness of the terrain, and because the warriors are very fierce and well-armed.’ By the 1980s, just a few Mixe villages were still left in isolation, and when Shapiro reached the top of his climb and walked into one, he was confronted with the strangest plant he had ever seen.

The plant was a type of maize known as Olotón, but it grew nearly twenty feet high and had a bizarre, captivating root system. Most plants grow with their roots underground, but this plant also had them sprouting from high up its thick stalks, reaching out into the open air. From these bright orange, aerial roots, shaped like fingers, there dripped a glistening gel. The maize was oozing mucus. Also remarkable was that any maize could grow so high up the mountain and in such poor soil. The Mixe village was so remote that no chemical fertiliser could ever have made it there. The local farmers weren’t even growing the maize in a milpa (from the Aztec term for ‘maize field’). In this traditional system beans are grown alongside the cereal to fix nitrogen into the soil. Somehow, these alien-looking plants were feeding themselves.

At least, that was the hunch Shapiro left with; that the strange mucus dripping from roots growing above ground was providing the plant with all the nitrogen it needed. The theory seemed unlikely. It broke all the rules. If it was true then this could be a game changer. Fertiliser costs farmers around the world billions of dollars a year and has great environmental costs, from the energy used to make it, to the greenhouse gases it releases, and the rivers and oceans it pollutes. The problem was that forty years ago, Shapiro had no means of testing his hunch.

Other scientists also made the climb up the ‘scorched hill’, but still no one could figure out the glistening mucus. Meanwhile, at the University of Wisconsin a microbiologist named Eric Triplett, who hadn’t seen the maize, or even known of the Mixe village, published a scientific paper in 1996 which set out a radical hypothesis: the ‘holy grail’ of cereals – maize that can take nitrogen from the air and feed itself – was biologically possible and could evolve. Such a discovery, he added, ‘would be of enormous economic value’ and would ‘improve human health’ as it would decrease the amount of nitrate in our water and in our food. For years, Triplett’s theory remained just that, a theory. He did, however, have some advice for any plant explorers setting off in search of this holy grail. Echoing Vavilov a century earlier, if something this extraordinary did exist, he said, it would be found close to the origins of maize, in its centre of diversity where its gene pool was greatest: southern Mexico.