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Fungus farm of a "primitive" farming ant, (c) Cauê Lopes. Ted Schultz, Smithsonian.Ants have been farming for far longer than humans have existed. They discovered fungus farming around fifty or sixty million years ago in the wet rainforests of South America, and have continued tending their underground fungus gardens through countless years as the planet changed and changed, and changed again. Much more recently — just a few years ago — I wrote about the fungus-farming ants (called “attine ants”), trying to imagine how they might view human agriculture. Our imaginary attine author closed with the hope that studying humans might help the attines understand their own history, “such as how the transition from primitive to advanced agriculture occured in our own ancestors”, and now a study by a group of humans has shed light on that very question.

Some species of attine ants are “primitive” farmers, cultivating fungi that haven’t been fully domesticated. The ants and the fungi both benefit from the relationship, but while the ants need the fungi to provide a crucial nutrient, the fungi are able to survive without the ants and can breed with their free-living relatives. The “advanced” attines, such as the famous leafcutters, grow fully domesticated fungi which can’t survive without their ant caretakers — the dependence is mutual and complete, just like our with our major crops.

To investigate how this happened, the researchers sequenced stretches of DNA from 119 ant species, 78 of which are fungus-farmers. Using this data and the geographic distribution of the ants, they built an evolutionary tree showing when and where particular traits (such as advanced agriculture) appeared. Their analysis revealed that advanced attine agriculture started around thirty million years ago, a time when glaciers spread across Antarctica and temperatures dropped around the world. As the world cooled, dry habitats like grasslands and deserts expanded through parts of the Americas.

Like us, ants excel at building and maintaining comfortable shelters, and some colonies managed to thrive in the drylands instead of the rainforest. That move proved crucial. In the drier habitats, the fungus crop needed the ants’ help to survive, needed the water they could provide and the shelter of their nests. Isolated from their kin, these fungi were set on an evolutionary course that entwined their fate with the ants: domestication.

This study resolved an evolutionary puzzle, but there’s also a broader message here. We tend to use mastery as a metaphor for our relationship with the world, casting it in terms of dominance and control, but like the attines, we are bound by ancient relationships and buffeted by greater forces. Domesticated crops may serve our needs, but only because we also serve theirs. And though our history may be shaped by social forces and steered by the decisions of individuals, our course is also pulled by other currents, shifts in climate and temperature that set wars and revolutions in motion. I’d love to learn more about the interaction between climate, geography, and human history, so if you know any good books (beyond Guns, Germs, and Steel), documentaries, or articles on the subject, please share them in the comments!

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Branstetter, M., Ješovnik, A., Sosa-Calvo, J., Lloyd, M., Faircloth, B., Brady, S., & Schultz, T. (2017). Dry habitats were crucibles of domestication in the evolution of agriculture in ants Proceedings of the Royal Society B: Biological Sciences, 284 (1852) DOI: 10.1098/rspb.2017.0095

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