Humans only invented agriculture some 10,000 years ago, but ants have been doing it for millions of years. New analysis indicates that, although ants operate farms in many environments, true domestication occurred 30 million years ago, in desert or near-desert conditions.
Attine ant species form a symbiotic relationship with fungi. The six-legged farmers propagate the fungus, providing it with nutrients and protection from other animals that might consume it more recklessly. In return, they get to eat the fungal growth.
Like bakers' apprentices taking precious starter dough to found their business, attine ants carry a small amount of fungus when they found a new colony. As with human agriculture, this has shaped the genetics of the species they farm, since varieties of fungus that best suit attine needs are more likely to be farmed.
Smithsonian Museum entomologist Dr Ted Schultz compared the DNA of 119 ant species, 78 of which are farmers. reporting his findings in Proceedings of the Royal Society B. He mapped the timing of when species diverged, using fossils for confirmation, to locate those closest to the trunk of the ant farmers' family tree.
The 250 known species of fungus-farming ants are divided into those that practice what is called "lower" and "higher" agriculture. Lower agriculture uses fungal species that can live without the ants' protection. Sometimes the fungus will spread beyond the colony to grow in the wild, becoming a resource for the ants to draw on if their crops fail.
Higher agriculture involves fungi that, like many human crops, have been so modified by the farmers as to be unable to survive independently. Since the ants cannot survive without their fungi, the two species are locked in mutual dependence.
Lower agriculture has previously been estimated to have begun in South America 55-65 million years ago. Schultz's work indicates higher agriculture dates back around 30 million years and began in a dry climate, contradicting previous assumptions of a wet origin.
Global climatic changes at the time dried much of South American out. Suitable ranges for rainforest fungi would have contracted, and Schultz thinks some were saved by ants that provided them with reliable moisture, collecting water for humidity-controlled fungal gardens.
"These higher agricultural-ant societies have been practicing sustainable, industrial-scale agriculture for millions of years," Schultz said in a statement. "Studying their dynamics and how their relationships with their fungal partners have evolved may offer important lessons to inform our own challenges with our agricultural practices. Ants have established a form of agriculture that provides all the nourishment needed for their societies using a single crop that is resistant to disease, pests, and droughts at a scale and level of efficiency that rivals human agriculture."
Given our own disastrous experience with monocultures, we've much to learn.
Ted Schultz (left) and Jeffrey Sosa-Calvo (right) excavate a lower fungus-farming ant nest in the seasonally dry Brazilian Cerrado (savanna). Photo credit: Cauê Lopes.The underground garden chamber of a primitive, lower fungus-farming ant colony. Higher agriculture colonies are larger. Cauê Lopes/Ted Schultz/Smithsonian