I was watching a nature documentary the other night about slime (The Secret Mind of Slime, PBS). Scientists have experimented on slime and discovered that it can perceive, process information, learn, memorize, and even decide. Slime is smart. Slime is intelligent. One of the scientists (“slimatologists”) speculated agreeably that slime could be the evolutionary origin of brains: because slime uses electrical circuits to conduct its intelligent business, and that is what the brain uses too. Electricity is the source of intelligence in slime and in brains, with brains just a more sophisticated form of slime. We must therefore think again before we denigrate something with the word slime. A slimy brain is a smart brain. In the course of elevating slime’s image, the program also drew attention to roots—because roots also turn out to be intelligent. They can perceive, learn, and decide—at least in a primitive form. One of the scientists put it by saying that the plant’s brain is under ground with its reproductive parts above ground, thus inverting the typical arrangement. He illustrated the point by producing a plant pot with a human doll head down in the soil, feet pointing upwards. It is as if the tree has its head buried in the earth with its limbs held aloft: the clever parts of the tree spend their lives under ground while the lowlier parts waft in the breeze. It is a striking image, illustrating the power of images, and one that set me thinking. Apparently two types of life-form are conceivable and even actual: a brain-up form like almost any animal you can think of, and a brain-down form exemplified in a primitive fashion in plants. Head in the air or head buried in the ground—two possible phenotypes, two evolutionary options.
This raises intriguing questions. Why haven’t plants capitalized on the brain-down option, having already blazed the trail? Why don’t we see sophisticated brains stuck in the ground while the rest of the organism pokes out above ground? Wouldn’t natural selection favor the emergence of such brains, as it has favored brains that float above the earth’s surface? Slime and roots are pretty impressive intelligence-wise, but why not ascend to the heady heights (so to speak) of lizards and llamas? Yet nothing like this populates our planet. That is an evolutionary puzzle to be set beside other evolutionary puzzles such as the origins of sex or consciousness. There seems no natural obstacle to it, and better brains are generally a good idea. The sense organs needn’t be buried as well, preventing them from responding to events above ground; they could hover in the clear air and relay their messages to the brain lurking beneath. After all, the sense organs of terrestrial animals are generally at some distance from the brain, with non-zero time intervals between reception and response. The eyes could be attached to branchlike structures (think giraffes) and still serve the visual cortex hidden under ground. The brain could then issue orders to sway or withdraw or bristle or spray poison—whatever might prove useful in the battle to survive. Plants already have ingenious ways of thwarting predators, and they could no doubt use some more intelligent adaptations orchestrated by a smart root-brain. Is it that given their niche they simply have no need for smarter brains? That is hard to credit: other things being equal, brains are handy organs to possess, which is why so many roaming animals possess them. Is it that plants don’t move and so don’t need brains? Now we are talking, but again this doesn’t really explain the absence of brain-down creatures, since it is not clear that locomotion is the sole reason that brains evolve. There could be plenty of aboveground limb motion to organize–and why shouldn’t the creature move around under ground? Why shouldn’t the brain-down creature be a burrowing creature? It might even withdraw its air-dwelling appendages as it burrows, thus making subterranean motion easier, protruding them again when it finds a new place to live; or it might simply slice through the earth with parts both below and above ground. There is no good reason why its dual ecosystem should rule out developing a bigger brain. So it is a real question why we don’t find truly intelligent trees with the brains the size of an elephant’s. After all, some animals are amphibious, or exist partially under water and partially above water: why shouldn’t the same be true of the earth medium? Wouldn’t the brain be safer ensconced under ground away from predators that exist only on the surface of the planet? That is how many whole animals lead safer lives, so why not keep the vital brain under ground with only the organism’s leaves and branches sticking out? Trees have been around for an awfully long time and you would think that evolving a better brain might have occurred to them. It seems peculiar that only brain-up organisms have taken advantage of this dandy little adaptation.
Imagine a planet on which things are very different: here there are many organisms that have adopted the brain-down lifestyle. It is nothing unusual, with colonies and even cities composed of such inverted (to us) creatures. They might have developed technologies that compensate for their relatively static mode of life, such as flying machines for delivering mail. They stay put but they like it that way (like Phillip Larkin). Perhaps the atmosphere on this planet is toxic to brains like theirs, or just too hot or too cold. In any case their brains do better comfortably placed under the planet’s surface; indeed, they might be the dominant life form on the planet, with the up-brainers relatively low in the biological order. Here it pays handsomely to store your brain snugly under ground. It is as if plant life has undergone the kind of acceleration that animal life underwent on planet earth during the Cambrian—with many types of intelligent and brainy organism now enjoying the partially belowground lifestyle. It may even be thought de rigueur to exist in this form—a cut above, so to speak. The brain-downers may find the brain-uppers rather a pathetic lot, not fully “evolved”, mildly absurd. Why carry your brain around in a bony box in the open air where it can easily get knocked about? Better to keep it within the soft embrace of the earth sheathed in a nice flexible waterproof membrane. Brain injury is virtually unknown among these creatures, and not having to keep the brain aloft enables brains to grow to enormous size. These are some seriously smart subterranean brains. So there is nothing logically problematic about the brain-down lifestyle—nothing contrary to sound biological theory. It is just an accident that earth is devoid of such eminently reasonable creatures. We brain-uppers suffer from a prejudice that makes us think that our way is the only way, but plants already contain the seeds of a different way of living—the head down, genitals up way.
From a broader perspective, indeed, the difference is not as great as we might parochially suppose. After all, plants do move around a fair bit: they sway and bend in the wind, they grow upwards and downwards, they drop their leaves, they swarm up walls, they send out their pollen, and they travel with the earth’s diurnal rotation and orbit round the sun. They are not the static entities we are apt to imagine. They are a lot livelier than mountains or rocks. On the other hand, how much do organisms equipped with legs or wings actually move? Some never stray far from their place of birth during their whole life, a matter feet in some cases. Even the sprinting cheetah doesn’t cover that much ground and is a good deal slower than light. From the point of view of the universe, things on planet earth are pretty sluggish, pretty earthbound. The brains of animals are stuck in the earth’s atmosphere, even if not buried under ground, and they really don’t move that much more than plants. To an alien species used to freer modes of travel, all of life on earth might seem as if it is rooted to the spot. And what exactly is the difference between under ground and over ground? In addition to the gases of earth’s atmosphere there is dust, water vapor, pollutants, flying insects, and birds—all contributing to the solidity of what we call the air. Compared to empty space, earth’s atmosphere is part of the ground, just a bit less cluttered (compare the oceans). And our heads encounter all sorts of resistance as we wander strenuously around: wind, water, obstacles, and projectiles. It is true that our brains are located above our feet, but in the wider scheme of things this doesn’t seem so crucial (consider snakes); and anyway they are not always above our feet, as when lying down or upside down. The difference between creatures with their heads in the sand or mud and creatures with their heads in the air is just not that deep. So, again, it is puzzling why we don’t find organisms whose brains are stowed under ground like roots. There is nothing about the location of our brains—and those of most animals on earth—that sets the standard for how a brain has to be located. Other brains might live out their days enjoying other accommodations. Other creatures might be like that scientist’s doll with its head stuck in the soil. Elsewhere in the universe subterranean slime might be the material basis of most intelligence.Co
 Let me note that it is the function of roots to keep a plant rooted in place (among other functions), i.e. to keep the plant at rest. This enables plants to avoid the depredations of wind and other forms of displacement—which less rooted organisms have more trouble with. As the function of legs is to enable movement, so the function of roots is to prevent it—both are locomotive functions. A tree is not like a rock, which doesn’t move as a matter of simple physical inertia; roots are ingenious devices of motion prevention.
 Someone should write a science fiction story based on this possibility entitled Slime Wars or Under Dune or Planet of the Trees. What about the idea of creatures whose brains exist at the center of their planet with the rest of their life conducted at the surface?