The soldier steps into the immense, dense forest of the Amazon. She sniffs the air — picks up rotting wood, flower nectar, a damp breeze — and trots out among the towering trees.
Behind her, below ground and out of sight, sits one of the world's strangest societies. Tens of thousands of farmers tend to a vast garden beneath the earth. Nurses care collectively for the community's kids. Sanitation workers scurry around the subterranean city, meticulously scouring it of waste and weeds; the unwanted material is then carried to a garbage dump far away. Jobs in this society are assigned at birth on the basis of the individual's size and shape. But all members serve at the will of their queen.
The soldier stops and smells something strange — she doesn't know it, but it's cream of wheat. She walks toward the smell, picks up its large, white source, and turns to carry it home.
"Found one!" Ted Schultz scrambles to his feet, his gaze locked on the white speck and the tiny creature carrying it. He and his colleagues follow the soldier back to its colony, pinpoint the entrance and begin to dig. It's not till they've burrowed through several feet of earth that they find what they're looking for: a massive, white, sponge-shaped fungus swarming with ants.
"A lot of non-biologists are attracted to things like butterflies or ladybugs — certain charismatic insects — and ants are not among those," said Schultz, back in his office in the entomology department at the National Museum of Natural History. "But actually I think if people could see what ants look like really close up they would change their minds."
In front of him sit several of the ant colonies he's collected over the course of his 26-year career. The communities inside the clear plastic boxes are miniature cities teeming with tiny life — the rare specimens in the museum's 145-million-item collection that are still alive.
Schultz's ants are farmers, and that white fungus he pulled out of the ground is their crop. Between 55 and 60 million years ago, an ancient insect evolved the ability to feed a fungus and live off of its spores. Now there are some 250 ant species that farm fungi — tending to them, weeding them, ensuring that they have the nutrients they need. They depend on the fungus for food, and in turn, the fungus depends on the ants to grow.
"It was immediately like, 'holy moly,' just a light bulb going off," said Peter Peregrine, an anthropologist at Lawrence University, recalling the first time he heard about these ants. "That's agriculture. That's really interesting."
For years, Schultz has been tracking these ants in the tropics and scrutinizing them in the lab in an effort understand how the creatures evolved into farmers millions of years before Homo sapiens even existed on the planet. But recently he's teamed up with anthropologists like Peregrine to look for parallels between people and ants. If they can find them, perhaps the history of human agriculture will help illuminate how farming insects evolved. And in return, Schultz believes, perhaps the ants can teach us humans something about ourselves.
It's a high calling for a tiny bug with a trifling brain. But Schultz has long known that ants are not to be underestimated. When he was 8, his mother gave him a book called "The World of Ants" (he still owns a copy), which included three pages on fungus farmers.
"I remember reading that and thinking, like, 'What?' " Schultz recalled. "How can something seemingly so simple as an ant, with such a small brain, do things like agriculture that are so complicated? That always kind of stuck with me."
Ant colonies illustrate a phenomenon called emergence: Parts of a system acting in very simple ways can produce collective behaviors that are incredibly sophisticated, without anyone telling them how. The same phenomenon explains how individual birds can form a flock, and how the millions of neurons in our nervous systems can create consciousness. Many entomologists argue that social insects like ants should be studied on the scale of the colony, rather than the individual — it's by acting as a community that these creatures do what they do.
"The original ant 130 million years ago was social," Schultz said, "and on that foundation of sociality all kinds of ant lineages have evolved very, very complicated behaviors."
An agricultural ant colony begins with a single member, the queen. She seeds her garden with spores carried from her mother's home, and gives birth to the workers who will cultivate it. As the new colony grows, worker ants fertilize the fungus with bits of plant material collected from the outside — flower pollen, chewed up leaves. The most massive colonies can defoliate an entire tree in a matter of days, given the opportunity (though trees have evolved their own defenses).
Some species have learned to "herd" aphid "cattle." The ants keep their bugs docile with tranquilizing chemicals the ants secrete from their feet (there are probably more than a few human cattle ranchers who wish they could do the same), then feed on the honeydew that the aphids excrete, much the way that humans drink cows' milk.
Schultz and his colleagues have reconstructed the evolution of these abilities by comparing the genomes of more primitive species with those of advanced ones. DNA analysis of the ants' fungi shows that the crops' evolution mirrors that of the species that farms them. Many of the ant species have adaptations that make them better farmers, including crevasses on their bodies containing microbes that produce an antibiotic they can apply to their crops. Likewise, the fungi have evolved to become more appealing to their ants.
"They're true farmers," Schultz said of his insects. "I suppose if you didn't want to call it farming you could also call it symbiosis. But then you’d have to also talk about human agriculture as a symbiosis too."
Strange as it may seem, humanity's relationship with our cultivars is a mutually beneficial one. Like ants with their fungus, we fertilize our crops, protect them from weeds and insects and help them spread around the globe.
"Domestication is really successful for the plant or animal being domesticated," said Peregrine, the anthropologist. "For example, corn began as this very localized, weedy grass, and now it's the most widely planted crop on Earth. ... So who is to say that corn doesn't have a stake in this relationship as well?"
Three years ago, after hearing about farming ants from one of his colleagues, Peregrine convened a meeting of archaeologists, anthropologists and entomologists at the Santa Fe Institute to discuss possible parallels between human farmers and insects (in addition to ants, beetles and termites have also evolved the ability to farm). Agriculture could be a rare example of convergent evolution — unrelated organisms evolving a similar trait — happening across entirely different orders of animal.
"We wanted to see, do the same sort of ecological rules and laws and forces govern both systems?" Shultz said.
The answer seems to be "yes." As was the case with humans, insects became sedentary when they became farmers. Initially, farming wasn't as profitable as being a hunter-gatherer — both primitive ants and early subsistence farmers are thought to have been malnourished — but as agriculture became more advanced, it became more productive. These more sophisticated farms were able to sustain larger populations, which promoted division of labor, which gave rise to incredibly complex civilizations. Farming societies built the pyramids and the Internet, wrote the Bhagavad Gita and "Pride and Prejudice," sailed the seas and visited the moon, and began to divine the fundamental nature of the universe.
And ants? Well, ants became one of the dominant ecological forces on the planet. If you weighed every living thing in the American tropics (there are no ant farmers in the Eastern hemisphere), agricultural ants would make up 25 percent of the weight.
"Ants are super successful," said Schultz, a hint of pride in his voice. "They really shape their ecosystems, way more than any large, charismatic herbivore."
Among both ant and human farming communities, all participants in the relationship have been irrevocably changed by it. Farming ants and their fungus have fundamentally different DNA than their non-farming relatives. Human farmers have evolved genetic adaptations that allow us to digest milk and metabolize fats; our crops, meanwhile, bear little resemblance to their wild ancestors.
That said, ant farmers are not directly comparable to people. They're not consciously manipulating their fungi (indeed, Schultz said, you can imagine a scenario in which the fungi rule the relationship, bending millions of tiny ant servants to their will). Ant agriculture is a product of natural selection, of innumerable accumulated genetic accidents. New strategies aren't learned, they're evolved. But humans have consciousness and culture, and that allowed us to achieve in a few thousand years what took ants five hundred thousand centuries to accomplish. Even though ants have been farming for much longer, Peregrine said, there isn't much they can teach us about agriculture that we don't already know.
"One thing that is really important and a little scary is that it places humans in the natural world," Peregrine said. "The development of agriculture, which we see as this great watershed in human history ... is not a unique moment. We have our own twist on it, and we do things way faster because we have culture, but at the base of it we are creatures that are subject to evolution just like all other organisms."
"Some people find that as taking away our humanity or something, but I find it humbling. It says, we’re part of nature too."
Tales from the Vault: Science museums are home to vast research collections, most of which the public never gets to see — until now. Once a month, Speaking of Science will go behind the scenes at our favorite museums to introduce readers to the fascinating objects and people we find there. Read past installments here.