Beneath the rain forest canopy, a low roar from insects builds to periodic crescendos as auburn- and tangerine-colored leaves bigger than dinner plates drift down from branches above. Scarlet macaws and yellow-ridged toucans issue raspy calls. Capuchin monkeys drop detritus from the trees onto four biologists who are inching their way along a stretch of Amazon rain forest, just a few hours’ drive north of Manaus, Brazil. Inside this vast tract of jungle, which runs unbroken for hundreds of miles to the Venezuelan border, they’re hunting for clues to explain an extraordinary evolutionary event.
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Somewhere near this spot 50 million years ago, after the dinosaurs disappeared, certain ant species began cultivating and eating fungus. Of all animals on earth, only these particular ants, several kinds of beetles and termites—and, of course, human beings—grow their own food. Somehow, this new tribe of ants, the attines, went—in anthropomorphic terms—from being hunter-gatherers to farmers. How and why they did so remains a tantalizing mystery.
Ted Schultz, a research entomologist from the Smithsonian Institution’s National Museum of Natural History, kneels with the intensity of a supplicant at the entrance to an ant nest. He has a mop of tar-black hair and eyes that resemble large charcoal orbs behind thick lenses. The object of his interest is a nest of leafcutters, the showiest of the attine ants.
Twenty feet up a nearby trumpet tree, the ants set upon freshly sprouted leaves, mandibles open, carving out elegant half-moons. They load these cuttings, which weigh up to ten times more than they do, over their backs and head for home, streaming back down the tree in an undulating line not unlike a band of tipsy piano movers. From a little distance, the ants, wearing stylish neon-green hats, look to be dancing.
Other streams of leafcutters flow from the shadows across brittle, dying leaves, into a clearing of vermilion sandy soil around craters in the dirt. They amble past larger ants with oversize mandibles standing vigil near the nest entrance, vanishing into long, curving subterranean channels, which open up to thousands of chambers spreading down and out through rock-solid dirt.