David Brin - The Heart of the Comet

“The same holds for the entire organism, Carl. A normal human being has countless species of creatures living in him, depending on him as he depends on them. From gut bacteria that help us digest our food, to a special type of mite that lives only at the base of human eyelashes, scouring them, eating decayed matter and keeping them clean.”

Saul spread his hands. “None of these symbiotic animals can live independently of man anymore. Nor can we very easily do without them. They’re almost as much parts of the colony organism called Homo sapiens as human DNA itself.”

Carl blinked, as if trying to absorb this new leap. “It’s like a quantum field in physics, then. The boundaries of what I call ‘me’ are… are…”

“Are amorphous. Nebulous. Difficult to define. You’ve got it! They’ve found that married couples share much the same suite of intestinal flora, for instance. Make love to a woman, and you exchange symbionts. In a sense, you become partly the same creature by sharing elements that grow and participate in each other.”

Carl frowned. And Saul realized that he was skirting a touchy subject. He hurried on.

“But here is my main point. Carl. Probably few, if any, of these symbionts simply settled into their niches without an initial struggle. Evolution doesn’t work that way… at least not usually.”

“But—”

“Every symbiont, from digestion helper to follicle cleaner, started out as an invader, once upon a time. Every synergism began in a disease.”

“I don’t…” Carl frowned in concentration. “Wait. Wait a minute.” His brow was knitted with tight furrows. “You spoke of disease as negotiation between a host and an invading.”

“— Visiting—”

“— species. But… but even if that’s the case, this negotiation takes place over the bodies of uncounted dead of both sides!” Carl looked up, eyes flashing. “True, they may come to a modus vivendi someday, but that doesn’t help the individuals who die, often horribly, broken on the wheel of evolution.”

Saul stared, unable to hide his surprise. In his most pensive moments, Carl Osborn seemed to have come upon a new facility with words. With tempering, an awkward youth had turned into something of a poet.

“Well said.” Saul nodded. “And that’s exactly what we’re seeing here on Halley. Some die abruptly. Others fight the interlopers to a standstill. Some even profit a little from some side effect of their infestation.”

Carl slapped the desktop with a loud report and swiveled to face Saul fully.

“All very well and good, Saul. If— if — there were only one or two diseases, and if we had generations, with millions of people, in which to work all this out.”

“But that’s not the case! Say you’re like that green-colored character up in Hydroponics Two.”

“Old McCue? The one whose skin parasite seems to feed him nutrients made from sunlight?”

“Yeah. Great stuff. But— to quote from your own report— the man’s mind has also been reduced to the level of a moron by a peptide byproduct of that very same fungoid parasite!”

The younger man breathed heavily.

“I’m glad you read my studies,” Saul answered.

Carl snorted. “Besides Jeffers, and Virginia’s computer, you’re the only one who writes anything worth reading, anymore. I’m sure you’ll be more famous than ever, when you send your reports to Earth.”

That made Saul wince. How had he managed to make Carl misunderstand him again? “It’s not like that.”

“Oh? Then how is it, Mr. Great Man of Biology? Tell me! I’ve shown you 1 know plenty, for an amateur. Convince me! Tell me how the hell all these fancy theories about symbiosis are going to make one slice of difference to a tiny, overwhelmed colony, every member of which is a total, certain goner!”

The pause lasted. Saul waited until the other man’s breathing had settled— until Carl had slipped back into the webbing on his side of the desk, glaring at him.

“I already told you, but you weren’t listening,” he said softly. “There is one person on this planetoid who’s in no danger at all. Someone with attributes that make him safe in a totally new way.

“That person is me, Carl.”

For the first time, the full point of the conversation seemed to hit the spacer. He stood up.

“You?”

“Me.” Saul nodded. “My sneezing, my perpetual dripping are only surface features of that ‘negotiation process’ we spoke of. And it seams my immune system is a perfect diplomat. Except for the damage to my reproductive cells, my body has taken all comers almost without trouble. It accepts or rejects every new lifeform in short order, and each one soon finds its own niche.”

There was another silence.

“I am quite serious, Carl.”

“But… how ?”

“How?” Saul shook his head. “I only know part of it, as yet. For one thing, I’ve inherited a rare enzyme that some have called N Complex . A dozen or so others on Halley have it too.”

“And are they…”

“More disease resistant? Seems so. But also, there’s something else, something in my blood that got there back when I worked with Simon Percell.”

“Yes?” Carl’s voice was flat now, his expression guarded.

“It’s called a reading unit. We only used the things for a couple of years, until we found better ways to strip and analyze DNA in vivo. Nearly forgot completely about the little things… until I saw them floating around down there, where they’d taken over my spermetic cells.”

Saul shook his head. “Don’t know how they got into me, really. Must’ve stuck myself one day while doing a gene analysis. But however they got there, my body’s using them, somehow.

“Now I think I know why I was so lucky, three decades ago, when I developed the new cyanutes. I didn’t really develop them. My body did.”

The longest silence of them all followed this.

At last Carl spoke.

“I’ve also read psychology, Saul. You know, of course, that claims of invulnerability are symptoms of paranoia?”

Saul shrugged. “I am, in almost every basic sense, completely healthy. Completely. The only one in the colony. You don’t believe me?”

“Of course not! What do you take me for?”

Saul held out his hand. “Take it,” he said casually. After a moment’s hesitation, Carl’s callused fingers wrapped around Saul’s, still soft from so long in the slots.

Carl’s grim smile faded into intense concentration as Saul squeezed, talking on, casually.

“Diseases, microgravity deconditioning, slot fatigue…they’ve pounded all of you down until a drugged Cub Scout could beat any of you with one hand tied.”

Carl’s brow beaded. Obstinately, grunting, he tried to match Saul’s grip.

‘You know you can’t t knish the Nudge Launchers in time, even with all of Virginia’s mechs to help. You need people, and you don’t have ’em, Carl. Two hundred slotted for good, another hundred feeble as kittens—”

He let go and Carl sagged back with a ragged sigh, his eyes wide.

“I didn’t show you this to rub your nose in your weakness, Carl. I only want you to believe it when I say there may be a way. A way to give similar immunity to many, maybe even most of the members of this expedition.

“Carl, we just may not be doomed, after all.”

He said no more. There was no point in talking any longer. When the other man had questions, he would ask them. Let it have time to sink in, he thought.

Right now, Carl’s face was like a statue’s. He stood up— rocky, unsteady— staring at Saul even as he backed away, shaking his head. With one hand he touched the doorplate, spilling phosphor light into the darkened room.