First steps in farming

Credit: Scott Solomon

The success of our species has been in part because of our use of agriculture, but it is not a uniquely human occupation. Some social insects — such as fungus-growing ants and ambrosia beetles — have developed quite sophisticated cultivation and harvesting routines. A more modest form of fungal husbandry has been adopted by marine snails, but it comes as something as a surprise to discover a primitive form of agriculture in the soil-dwelling social amoeba Dictyostelium discoideum, familiarly known as slime mould. About one-third of D. discoideum clones isolated from the wild refrain from consuming all the available bacteria at a site, instead incorporating them into their reproductive assemblages. This ‘harvest’ is carried by the spores during dispersal and serves to seed a new bacterial crop at their next location. The connection between farming and sociality — in humans, insects and these symbiotic microbes — may be more than a coincidence since the multigenerational benefits generated are enjoyed by already established kin groups.