Generations of students have learned that the dawn of settled agriculture, some 12,000 years ago, was a revolutionary change in human social development. When our ancestors domesticated plants and animals they created reliable food supplies, and with them grew cities and the fruits of advanced civilization and culture. Farming, we believed, was one of the things that set us apart.
But it turns out that we’re not so unique after all. In fact, compared to some species, humans are late to the game. Ants began farming fungi a staggering 65 million years ago, soon after the days of the dinosaurs. Ambrosia beetle and termite species have also raised such crops for eons—as evidenced by a 25 million-year-old fossilized nest. Damselfish cultivate gardens of algae, and some ants have even developed a form of animal husbandry that includes shepherding stocks of aphids and mealy bugs.
“Agriculture is a thing that’s happened repeatedly in the animal world, and we’re just one of those animals,” says Ted Schultz, an entomologist who heads up the AntLab at the Smithsonian’s National Museum of Natural History.
Schultz coedited The Convergent Evolution of Agriculture in Humans and Insects, a new book that explores the fascinating ways in which human and nonhuman farmers compare, and asks what we might learn from other agricultural species.
Are Other Species Really Farmers In The Same Way We Are?
When a termite feeds pre-chewed plants to its fungi, is it really the same thing as a human farmer fertilizing a soybean field? When ants milk mealy bugs for sweet secretions, is it actually akin to dairy farming? Schultz thinks about these similarities by using another example in the natural world—bird and bat wings aren’t identical, he says, but they are both wings.
“That kind of sameness isn’t by chance,” he notes. “It’s because they both had to tackle the same problem. Agriculture is the same in that sense. Instead of going out there and finding food, and eating it, you are cultivating your own food.”
Farmers of any species have to prepare their fields and plant their crops, battle weeds and parasites, and harvest the fruits of their labor. When they move to new locations they carry starter stocks to begin anew.
“I love the image of an ant flying off with a single (pregnant) mealy bug in its jaws, and it’s going to start a whole colony of mealy bugs from that one individual,” says Joan Strassmann, an evolutionary biologist at Washington University in St. Louis.
Perhaps most importantly human and other farmers all change once-wild cultivars into new domesticated species of plants or animals, modifying them to the extent that they become dependent on farmers for their survival.
Dorian Fuller, who studies the origins and evolution of agriculture at University College London, says on a basic level agriculture is a form of symbiosis, where two species have coevolved a relationship in which one is promoting the growth of another to feed off of it. “In that sense, what humans and insects do is the same,” he notes.
Fungus-growing ants, some 240 species, live across the Americas and the Caribbean. When they emerge en masse to forage they don’t collect food, they collect fertilizer. In leaf-cutting ants, arguably the most evolutionarily modified of the fungus-growing ants, droves of the ants gather tiny pieces of vegetation and take them underground where their gardens of fungi await. The edible fungi are raised by the ants on an industrial scale, sequestered in microclimates that offer no escape and thus create genetic isolation. The fungi found growing in ant-tended gardens has become so adapted to the arrangement it isn’t found in the wild, and is entirely dependent upon the work of the ant farmers.
Like the ants and their fungi, most farming species genetically coevolve with their crops over countless generations, so that each becomes entirely dependent on the other. In fact, it can sometimes be debatable exactly which of the species drives the arrangement. Ant behaviors and lifestyles, for example, have become entirely dependent on growing and eating fungi. And the relationship is deeper than behavioral. “You could easily say that the fungi domesticated the ants, because the ants are genetically changed,” Schultz says, citing results of ant gene studies. “They have become dependent on the fungi and they probably can’t go back.”
Human farmers, at least in our minds, are clearly the dominant species in our own agricultural systems. But, like the fungi, the crops and domesticated animals of human farmers do benefit from the arrangement. Wheat, rice and maize are likely the grasses with the highest biomass in the world. Chickens may be the most populous bird on the planet while their ancestor, the red jungle fowl, persists only in a few limited habitats.
“In a kind of Darwinian sense those domesticated species have benefited massively, you could kind of read it of them driving the relationship,” Fuller says. But domesticated crops are dependent on human engagement to persist in that relationship—and humans have choices. “If humans stop planting wheat in America or Britain, the wheat can’t really reproduce itself.”
Ancient agricultural sites repeatedly show that scenario, yielding extinct strains of former farm crops that humans chose to abandon in favor of something else. That’s something that nonhuman farmer species can’t contemplate.
“The real difference is that humans, once they move into an agricultural cultural system, start to domesticate lots of things,” Fuller explains. Humans are not genetically fixed to any particular agriculture because our agricultural evolution has been a cultural, rather than a genetic evolution.
We grow and eat many different foods. All the species domesticated, from wheat to goats, play different roles, some provide protein, some provide oils or textiles. That’s an arrangement really not found among nonhuman agriculturalists, which tend to have one-on-one relationships with a few interesting exceptions.
In damselfish, scientists have discovered an exceedingly rare kind of agriculture involving the first known case of a nonhuman vertebrate domesticating another animal. Longfin damselfish raise, and live on, algae that they farm on coral reefs. “The algae that grow in those gardens really can’t grow anywhere else, they are vulnerable to being outcompeted by other kinds of algae,” says Strassmann.
But the fish also herd swarms of tiny mysid shrimp, floating clusters that fertilize the algae with their waste to provide a better crop. In turn, the damsel fish protect these farmer’s helpers from being eaten by other fish species. “It’s hard to evolve a new trait, it’s a lot easier to capture someone else that already has that trait. That’s really what’s going on here,” says Strassmann.
Why Does Agriculture Happen At All, And Why So Infrequently?
Humans have adopted agriculture at least a dozen and likely more than 20 different times, as recently as 4,000 years ago and as far back as 20,000 years or more. Though a handful of other species have adopted agriculture, their numbers are tiny when stacked up against nature’s predators, grazers and gatherers. If agriculture isn’t uniquely human it’s still extremely rare. And adopting it isn’t a simple matter of intelligence, since primates and dolphins don’t farm while slime molds do, cultivating crops of bacteria.
So why do select species settle down to farm? “It takes a lot of contingencies co-occurring for it to be successful and that alignment can be kind of rare,” Schultz says. Future farmers must first be foragers who store and distribute food at a central location. The species they already use have to be naturally suitable for domestication, and then must undergo favorable genetic changes for many generations. The process also requires a period of favorable and stable climate.
This is the path our hunter-gatherer ancestors followed, gradually engineering local ecosystems to slowly domesticate favorable weeds or fruits, or animals from dogs to ducks that tended to hang around near human settlements.
Nonhuman farmers also tend to be highly social species that communicate with each other and share resources. Over evolutionary time, insect farmers divide up the chores of raising crops, and work together to produce a communal food source that in turn benefits all. When Fiji’s ants live on and eat the Squamellaria plant, then fertilize it with their poop to sow the seeds of a new crop, the behavior is genetically hard-wired as the product of long evolution.
Our own case is very different. “A baby isn’t born knowing how to farm,” Schultz says. “It’s cultural evolution, and that is much faster and much more malleable than genetic evolution.”
Can We Learn From Nonhuman Agriculture?
Earth’s population is booming, its climate is shifting, and human farmers are in need of better, more efficient agriculture. Can we learn from species who’ve been at it for millions of years?
Nonhuman farmers don’t make conscious choices to be sustainable. But being part of an evolving ecosystem for countless generations may create natural efficiencies. “I think, through trial and error over 66 million years in the case of the ants that I study, the way that they practice agriculture has been optimized,” says Schultz.
Some ants control pests like mold with antibiotics secreted by bacteria that they cultivate on their own bodies. This arrangement has proven effective for so long, it seems likely that the antibiotics continually evolve, as the mold does, to be sustainably effective. Might these insect systems hold the seeds for pest control options better than chemicals to which pests continually evolve their own resistance?
Nonhuman farmers, whether ants growing fungi or fish growing algae, also raise clonal crops—meaning they are genetically identical. “What we’ve really learned from the biological systems is that plants grown in close proximity, as clones, do better,” Strassmann explains. When a crop is genetically homogenous there’s no evolutionary pressure to compete so plant resources instead fuel better productivity. But the arrangement is dangerous, because genetically identical crops can be wiped out more easily by a single pathogen.
Humans promote crop diversity to hedge against such dangers, but nonhuman species seem to weather them just fine. “How do they manage to have a single clone kept for so long without all the vulnerabilities of having a single clone?” Strassmann wonders. “If we could find ways to reduce the conflict within a field of plants, we can achieve higher yields, but that’s a complex thing to do.”
Nonhuman farmers also tend to occupy different spaces within the greater ecosystem.
For example, leaf cutter ants function like giant herbivores, a colony’s ants weigh as much as a cow and also eat a cow’s share of grass and leaves. But unlike large mammals, the ants don’t overgraze all the vegetation in the area around their colony.
With their numbers in the millions they are more diverse foragers, yet that’s not the only reason. Local plants and animals have coevolved with the ants and developed defenses against them. When being devoured some trees express chemicals into their leaves which make them unappetizing to the ant’s fungi crop. “Within a day or so their gardens start doing poorly, and the ants realize they need to move on and feed elsewhere,” Schultz says.
Developing that kind of dependency takes a long time. But some human farmers are becoming attuned to the benefits of integrating the local environment instead of entirely replacing it. Some coffee plantations, mingled with rainforest species, have reported fewer problems with pests. On North America’s Great Plains strips of native prairie, interspersed with crops, may help with everything from crop yield to erosion.
“I think as we develop agricultural systems we want them to be much more embedded in their environment,” Schultz says, “and the protocols we use for controlling things like pests and weeds may need to be informed more by evolutionary principles.”
If humans hope to farm for another 65 million years, to match the ants, embracing their kind of balance with the environment may be a great place to start.
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