On one earth, mice planted orchards.

Monkeys eat fruit. They throw the seeds away or swallow and excrete them, effectively propagating whatever tree it is that feeds them. Rodents, however, have ever-growing, iron-reinforced incisor teeth, which they use to gnaw through wood, nuts, and seeds. This behavior, of course, does not propagate the food plant.

Unless it does. The ancestors of Fling were not exactly squirrels1, but they also had a habit of burying caches of nuts, which sometimes sprouted. Like the even more distantly related beavers, they gnawed through the bark of living trees to get at the sugary cambium. This killed the tree, but, importantly, never the same kinds of nut trees that these rodents depended on for food. Unconsciously, they planted and weeded their groves.

At first, these rodents simply piled up the dead branches of the trees they killed. Some of the weed-trees, however, were acacias of the sort called "myrmecophytes." These grew special chambers in their flesh to feed and house colonies of ants, which returned the favor by fertilizing and defending their home trees.

The orchard mice appreciated this intricate mutualism by eating the ants. The gift of protein rewarded those mice that cut down and gathered more acacia branches. Rewarded even more highly were those mice that cut acacia branches and stuck in them in ground where they could take root.

Soon, central Africa was dotted with groves of nut trees, surrounded by thorny, ant-infested acacias, tended by families of large, well-fed, silviculturally-minded rodents.

Then the climate changed and the jungles dried up.

There followed the familiar runaway feedback loop of cooperation, social sense, and reason. Familiar, except for the brain parasites.

Toxoplasa gondii is a single-celled parasite related to the malaria-causing Plasmodium, more distantly to the red-tide causing dinoflagellates, and even more distantly to kelp.2 Kelps and other brown algae are generally inoffensive, but T. gondii's clade gave up on photosynthesis in favor of parasitism.

These single-celled organisms burrow into the cells of cats, where they steal ATP, disrupt pro-apoptosis effector proteins, and perpetrate other nefarious deeds.3 The most famous crime of T. gondii, however, is the way it spreads itself from cats to their prey and back again.

Step 1: cat eats mouse. Step 2: T. gondii cysts between the mouse's muscle and brain cells hatch into mobile tachyzoites. Step 3: tachyzoites produce oocytes, which come out the other end of the cat's gut in the usual way.4 Step 4: mouse eats cat poop, but ignore that for a moment because what's even worse is step 5: the ingested T. gondii burrow into the brains of the mice and start changing their neurochemistry.5 When they smell cat urine, infected mice run toward it. A pounce and a bite later, we arrive again at Step 1.

Consider the effect of toxoplasmosis on an intelligent rodent. Granted the blessings of self-awareness and ratiocination, does it realize that its urge to run out onto the Veldt and be devoured by lions was caused by brain parasites? Does it exercise its budding will-power and resist the temptation?

No. It rationalizes.

The dawn of Toxoplasmotic civilization began when an intelligent rodent looked out beyond the hedge-walls of its home grove and thought that's where I belong.

The predator-rich night! Sniff that danger and opportunity! I will run there, yes! I will bound! I will throw myself into the teeth of adventure! And if I come back, it will with my cheek-pouches stuffed full of discoveries!

Some did. Those groves with a few—not too many—toxoplasmotics found themselves prospering. New varieties of nut and ant-thorn tree, new allegiances with distant groves, new ideas. Careful tending of the god-cats and their ecstatic ceremonial victims led to selective breeding of different strains of T. gondii, each with subtly different neurological effects. When they discovered the microscope, things sped up a great deal.

Oh, the tilted towers they built! The glorious maze-cities. The space-craft that zigzagged around the solar system, seeking out new forms of danger. The staggering number of religious wars.

The Toxoplasmotic civilization that eventually contacted the Convention of Sophonts was considerably tamed. The vast majority of the population was infected with ritual strains that produced no significant behavioral changes. Only arch-traditionalist cultic priests gave their brains over to the old, fierce parasites. Fling was one of these.

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"Honored Sophont, please convince your brain to forgive me," she said. "My nose smelled primate sweat and my ears heard a plains ape's footfalls, so I allowed my neocortex to assume that you, honored person, were Mr. Grumbles."

The sun glowed on her white, tan, and gold vestments—heavy paper folded like the carapace of an origami pill bug. Tasseled fringes blended with the white fur from which her stilt-like hind legs protruded. Her tail swept a luxurious plume up behind her back, which peaked over her shoulders, then hunched sharply back down. The high, segmented dome formed by her vestments parted at the front into an inverted V, framing her face.

"My ears hear I have made a mistake and my brain swarms with curiosity."

Another Toxoplasmotic would have observed the black, white, and tan stripes that radiated from the eyes to recognize the Admirable Self-Flinger. To Koen, though, her face was dominated by scimitar ears, black welders' googles, and thumb-sized, orange teeth.

"A dormouse," he said.

Self-Flinger's right ear swished like the baton of an orchestra conductor. "I forgive your faux pas, since after all, I called you a monkey."

"Oh! That's all right. And I apologize!" Koen flapped his hands, which annoyed General Graa.

He exploded off of Koen's shoulder like a feathered bomb and flapped into the acacia, screaming.

"Self-Flinger, Mr. Grumbles has gone missing. I am very upset and impatient and lonely!"

"You're holding up well." Self-Flinger gave a little hop, turning her body to face the tree. "Is there anything I and my body can do to help?"

"Tell me if you know any pertinent information."

"My hippocampus does not know."

"Then spread the word! There's a pet-thief on the loose."

Self-Flinger lifted a leg, stretching out a foot-hand to pet her jaguar. Her arm-hands stayed folded under her chin, supported by her staff. "My brain worries about what such a thief might want with a pet plains ape."

"I am worried! I'm sick with worry. Mr. Grumbles is of the finest stock. Some nefarious thief could make a fortune selling him to collectors." The crown of the acacia bounced with the Pick's bobbing. "I am furious and eager to fight! But I will not peck their eyes or claw their bellies or devise elaborate traps for them. I will pay them. I will pay them anything. Any ransom to get back my steed…" Graa hopped from branch to branch within the tree, making haw-haw noises. "I am crying."

"My insular cortex reacts in empathy with yours," said Self-Flinger. "But I prune back my passion in this serious time and call upon my outermost cortex to consider the situation." A scimitar ear twisted toward Koen. "My mouth asks: what part do you play in this, Honored Sophont?"

Another moment of truth. Who better to confess to, than this mouse-monk? But Koen kept himself frozen. "I—I don't know," he said.

Self-Flinger brought her cane to her teeth and absent-mindedly gnawed off a curl of wood. "My hippocampus doesn't remember seeing your species before."

"I'm human," said Koen, "from the United Nations embassy."

She hopped around. "With a body of some close kin to the Picks' domesticated steeds?"

"That's right. Our species are very similar, so I feel some empathy with Mr. Grumbles." Which is why I stole him away from that mad bird, Koen almost said.

He stared into his own face, reflected in Self-Flinger's black goggles. He swallowed, mouth suddenly dry. What if it knew, this giant rat? What if it pointed one of those clawed fingers at him? Or leapt for this throat with those teeth? Her smell was dry and sweet as old manure.

"Your insular cortex feels empathy, does it?" Self-Flinger said. "Then I pity you. The next step of your search will be hard on you and your body."

General Graa popped his head out of the tree. "I am annoyed that you are dictating our angle of attack. I have not told you my next step, which is to contact the kennel club and commiserate with them over fermented blackberries."

"No, it isn't." Self-Flinger hopped around, ears pointed up at the tree branches. "Your body's distress has distracted you, Graa, because your next step is obvious." The Toxoplasmotic's whiskers quivered as she took another bite of her cane. "The exotic meat market."

1Technically they were stem-Sciuromorphs, equally distant from dormice and squirrels and the enigmatic mountain beaver.

2Cavalier-Smith, Thomas (2018). "Kingdom Chromista and its eight phyla: a new synthesis emphasising periplastid protein targeting, cytoskeletal and periplastid evolution, and ancient divergences". Protoplasma. 255 (1): 297–357. doi:10.1007/s00709-017-1147-3.

3Besteiro S. Toxoplasma control of host apoptosis: the art of not biting too hard the hand that feeds you. Microb Cell. 2015 May 30;2(6):178-181. doi: 10.15698/mic2015.06.209.

4Dubey, J. P. (2010). "General Biology". Toxoplasmosis of Animals and Humans (Second ed.). Boca Raton, London, New York: Taylor and Francis Group. pp. 1–20.

5They hypomethylate arginine vasopressin-related genes in the medial amygdala. See Hari Dass SA, Toxoplasma gondii infection reduces predator aversion in rats through epigenetic modulation in the host medial amygdala. Mol Ecol. 2014 Dec;23(24):6114-22. doi: 10.1111/mec.12888.