Adventures Among Ants - Mark W. Moffett [131]
OF ANTS AND MEN
Close examination of the evolution of leafcutters from lower attines suggests uncanny parallels with the history of human agriculture. Some early records of human subsistence farming document marginally domesticated species: like the lower attines, farmers frequently added wild specimens to their breeding stock, which in turn sometimes went wild, as cassava does in the Amazon. As a result of their limited inbreeding and frequent crossbreeding with free-range populations, the crops of lower attines and subsistence farmers were hearty, buffered from disease and environmental change by their genetic versatility. Since they weren’t strongly modified for cultivation, however, yields were low, limiting the societies of lower attines and subsistence farmers to a few hundred or few thousand individuals.
The emergence of fully domesticated crops—modified for high yield in such a way that they are no longer able to revert to life in the wild—has permitted both leafcutters and modern humans to scale up their farming efforts to fully exploit novel resource opportunities such as those available in open habitats. Not that their lives have been made easier by it. Early on, human farming turned into backbreaking, multistep work that became the only viable option for survival when the press of high populations made a return to harvesting wild food impractical, a difficulty referred to as “the plant trap.”35 Leafcutters likewise invest massively in maintaining their gardens. Their specialized laborers, who, in addition to their other tasks, must still forage, but now to feed their fungus, toil at a tempo no less exhausting than that of their more predatory sisters, from army ant to weaver ant. But the efforts of both leafcutters and people have in turn supported (and to some extent required) their big populations. The agriculture-fed civilizations of both exploded in size, eventually into the millions.
Humans have been adept at cultivating many species, as reflected in our urban diets today. No ant has achieved this versatility (although those feeding on honeydew often tend several insect “cattle” species). The colonies of both lower attines and leafcutters subsist on a single cultivar, growing no more than one kind of fungus in a nest. All leafcutters, in fact, rear the same fungal species. That fungus comes in many subtle varieties, however, and each colony devotes itself to one strain, propagated by asexual cuttings in much the same way humans farm bananas. That strain is established by the tiny, and as a result probably genetically uniform, sample of fungus the queen uses to start her nest, which she carries on her mating flight in the same pouch in her cheek that her workers use to gather up disease organisms and debris.
The gardens’ isolation underground must help keep a fungal strain pure. At the same time, ants will actively work to maintain genetic purity. If a scientist transfers a clone from one nest to another of the same species, for example, the ants will weed it out, even though it should serve them just as well as their own strain. Whether today’s ants can detect and select improvements in their stock, judging differences in nutrition or yield, is unknown. Their predilections may amount less to selection for the ideal fungus meal than to a kind of imprinting on its chemistry—flavor or odor—much as ants imprint on their nestmates; like people who insist on particular childhood recipes, gardening ants seem to tolerate only what they are familiar with, relegating anything else to the trash heap.
Still,