A slime mold is precisely the sort of thing you don’t want to step in. That also means figuratively, if you’re the kind of person who likes their taxonomy neat. That’s because slime molds aren’t molds at all… except for a few species that are. And while some of them are very slimy indeed, they usually aren’t. What?
The aptly-named Dog Vomit Slime Mold.
If not a fungus, usually, what is a slime mold? Either a giant amoeba, or a collection of amoebae. A plasmodial slime mold is essentially one giant cell with thousands of individual nuclei: a gross puddle of cytoplasm. But a cellular slime mold, my favorite kind, is a loose assembly of individual amoebae who, when a chemical signal is released, band together to form one creeping pile of neon goo that patrols the undergrowth, hunting for new bacteria for its component amoebae to munch, and creating a reproductive organism. For an analogy, imagine a herd of caribou on a wide open expanse of tundra, each browsing on lichen and moss by itself. But instead of migrating as a herd when they’ve finished off all the moss on the meadow, the caribou exude a pheromone that tells them to meet in the center and merge into one Super-Caribou that then takes off in search of more moss. Some caribou become the hooves, some the antlers. Some become the Super-Caribou’s testicles, producing sex cells for future use.
All the ones on the right are going to become the ears. The ones on the left… you don’t want to think about it.
Slime molds may not have antlers — or many discernible features at all, really — but they do have sex cells. Incredibly, some of the amoebae will sacrifice themselves to become the cells of the stalks that elevate the colony’s sori, or spore-producing organs, while others become the sex cells which will produce the spores themselves. In this way, the amoebae that make up a slime mold are like stem cells that act freely and independently of each other when feeding, then become differentiated when they join to become a multicellular organism. Like the Portuguese Man-of-War, it is an animal made of smaller animals, or more appropriately, a fungus-like thing made of smaller amoeba-like things.
Teamwork rhetoric aside, being the sex cells is a pretty highly coveted position among the amoebae.
But here’s the exciting part: it turns out that certain slime molds have developed agriculture. In a recent study, it was found that certain amoeba “cells” in Dictyostelium discoideum, a species of slime mold, could actually cultivate the very bacteria that the organism eats in its sori. That’s right: a brainless, de-centralized collection of unicellular organisms learned how to farm. If this doesn’t instantly impress you, think about how many other organisms out there purposefully cultivate their own food: it’s pretty much the leaf-cutter ants and us. Farming may not seem sexy to some people, but the difference between hunting-and-gathering and making your own nourishment where you live was a quantum leap made a mere ten thousand years ago that established human dominance over the Earth. Art, science, technology, and civilization itself came from the simple act of planting a seed.
Imagine a tribe of nomads in a Mesopotamian valley, circa 8,000 B.C. Following their chieftain’s orders, they have returned to this field at the time of what would someday be known as the Harvest Moon. It is true, there is better game to the North, but two years ago, a young woman who had been picking berries had had the foresight to sacrifice some berries to the gods by burying them in Earth. Give to the gods, she reasoned, and the gods would give back to the clan, and the chieftain agreed. Now that the berries are ripe and purple along the trails, as they always are during that cooling moon, the chieftain has remembered the field of their tribute those years ago, and directs his wandering clan to the sacred ground. Indeed, the gods have smiled on their sacrifice: purple berries grow everywhere in thick brambles, fluttering with birds. The clan eats well and sleeps happily for the next three nights, staining their softened teeth with berry juice and hunting the boar that have come to this thicket seeking their share of the birds’ feast. The woman who first planted her humble sacrifice of berries did not know that what she left in the soil to awaken slowly was the seed of civilization, from which the garden of art and science and cities would spread its fruit over the Earth.
Over the years, and after many seasons of sacrifice to the soil, the clan stays closer to the sacred field, guarding its wealth jealously against the other roving families. They become the first farmers. The visionaries among them possess crucial imagination, planting the grasses whose grains they thresh from the stalks and eat in great fistfuls. Others have the wisdom to plant olive and pomegranate trees that will not fruit until newborn infants have become mothers themselves. It is a hard life, hacking at the soil with sharpened sticks to impregnate the wilderness with date palms, but at least they have ceased their constant journeying. (That is, except for the hunters, who must travel farther and farther into the hills to find animals.) The clan, much larger in number now, still fashions spears and arrows with which to defend their orchards, but the clever ones modify them to ease the back-breaking work of cultivation. It is easier to cut millet with a sickle than a knife, to dig with a shovel rather than a spear.
And so the sword becomes the ploughshare, and technology eases work even as it gives mankind the capacity to work even harder. The plough is eventually hitched to the ox, and gives way to the tractor. The abacus, used to calculate quantities of grain, becomes the computer, which marries the rain with the automated irrigation system. The grasshopper-eating sparrows in the berry shrubs become the cropduster, then ascend higher to become satellites that track stormclouds and measure the relative greenness of desert fields for farmers who live hundreds of miles away in great cities. The ox gives way to a new technology, the slave, which becomes the sharecropper, which is crushed under the wheels of the remote-operated thresher like a nest of dormice. The thresher, once controlled by a distant hand at a keyboard, gains a level of sentience and becomes a robot. And the robot plants its own seeds: the nanobots.
I just pulled one of these on you.
Nanobots, or nanites, are machines built so small that they are invisible to the naked eye, often constructed from single molecules. They exist mainly in the hypothetical, but already some impressive examples of nanotechnology has proven their potential as the next dominant tool. Organic nanites have been constructed using bacteria and nucleic acids, and there has been one case in which scientists built a nanorobot car out of a single molecule. The most promising use for nanotechnology has been in the field of surgery, where microscopic robots could repair bodily damage at the cellular level. But I suspect, on a hunch, that the nanites of the future might be used for the same purpose as the very first technology: for agriculture. If we can build a microscopic car, why not a microscopic tractor? If nanorobots can repair the cell of a human body, why not use them to attack diseases in the roots of a corn stalk?
One of the science fiction genre’s favorite doomsday scenarios involves a substance we call “grey goo.” If nanorobots can reproduce themselves, which they would have to in order to be cost-efficient, they could conceivably replicate themselves indefinitely, consuming organic material to power their robot bodies. The result of such replication gone amok might be a “grey goo,” a liquid machine made of smaller, microscopic machines, reproducing exponentially until it has entirely swallowed all life on Earth. Technology, which made cultivation and thus civilization possible, eventually supplants and destroys both.
The idea of robots in the soil seems like a far-fetched nightmare to me, but I don’t doubt that it’s been and being considered by corporate agri-businesses in the increasing mechanized, anti-life form of farming we have today, so it’s worth our consideration. How would those future scientists limit our organic machines so as to avoid the “grey goo” scenario? We make them function like slime molds. Imagine a teaspoon of soil, filled with bacteria-based robots, each individual machine browsing on pathogenic bacteria. When this fuel source runs out, a chemical or electronic signal gathers the nanites together into a reproductive stage, a slime bubble of sorts, from which a sort of robo-sexual cell is produced. But with the robot gametes, in a special chamber: a nursery for the bacteria that fuels the robots. The robots that do our farming are farmers themselves: self-sustaining, capable of nourishing themselves. And from there? Evolution, with the now “sexual” machines changing with successive generations. Robot leaf-cutter ants. Robot civilization. Robot cities. Instead of a grey goo, the world ends in a new regime made of animals made of smaller animals.
Still far-fetched sci-fi nightmare? Yes, I hope. But it’s worth meditating on. Revolutions are born from cultivation, and gardens lead to new wildernesses. Though the humble slime mold isn’t poised to take over the Earth with its farming skills, this is how empires begin. And the slime molds, those dualistic and protean biological force living under the leaves of a forest floor, have already established their subtle empire.