Permutation City

The red-tagged molecules wandered the cell at random, part-digested mixed with raw indiscriminately. Neat process diagrams of metabolism -- the real-world Embden-Meyerhof pathway, or the Autoverse's Lambert pathway -- always gave the impression of some orderly molecular conveyor belt, but the truth was, life in either system was powered by nothing at the deepest level but a sequence of chance collisions.

A few red tags turned orange. Stage two: an enzyme tightening the molecule's hexagonal ring into a pentagon, transforming the spare vertex into a protruding cluster, more exposed and reactive than before.

Still nothing new. And still no hint of violet.

Nothing further seemed to happen for so long that Maria glanced at her watch and said "Globe," to see if some major population center had just come on-line for the day -- but the authentic Earth-from-space view showed dawn well into the Pacific. California would have been busy since before she'd arrived home.

A few orange tags turned yellow. Stage three of the Lambert pathway, like stage one, consisted of bonding an energy-rich group of atoms to the sugar. With nutrose, there was a payoff for this, eventually, with twice as many of the molecules which supplied the energy ending up "recharged" as had been "drained." Stage four, though -- the cleaving of the ring into two smaller fragments -- was the point where mutose gummed up the works irretrievably . . .

Except that one yellow speck had just split into two, before her eyes . . . and both new tags were colored violet.

Maria, startled, lost track of the evidence. Then she caught sight of the same thing happening again. And then a third time.

It took her a minute to think it through, and understand what this meant. The bacterium wasn't reversing the change she'd made to the sugar, converting mutose back into nutrose -- or doing the same to some part-digested metabolite. Instead, it must have modified the enzyme which broke the ring, coming up with a version which worked directly on the metabolite of mutose.

Maria froze the action, zoomed in, and watched a molecular-scale replay. The enzyme in question was constructed of thousands of atoms; it was impossible to spot the difference at a glance -- but there was no doubt about what it was doing. The two-atom blue-red spike she'd repositioned on the sugar was never shifted back into its "proper" place; instead, the enzyme now accommodated the altered geometry perfectly.

She summoned up old and new versions of the enzyme, highlighted the regions where the tertiary structure was different, and probed them with her fingertips -- confirming, palpably, that the cavity in the giant molecule where the reaction took place had changed shape.

And once the ring was cleaved? The fragments were the same, whether the original sugar had been nutrose or mutose. The rest of the Lambert pathway went on as if nothing had changed.

Maria was elated, and a little dazed. People had been trying to achieve a spontaneous adaptation like this for sixteen years. She didn't even know why she'd finally succeeded; for five years she'd been tinkering with the bacterium's error correction mechanisms, trying to force A. lamberti to mutate, not more rapidly, but more randomly. Every time, she'd ended up with a strain which -- like Lambert's original, like those of other workers -- suffered the same handful of predictable, useless mutations again and again . . . almost as if something deep in the clockwork of the Autoverse itself ruled out the exuberant diversity which came so effortlessly to real-world biology. Calvin and others had suggested that, because Autoverse physics omitted the deep indeterminacy of real-world quantum mechanics -- because it lacked this vital inflow of "true unpredictability" -- the same richness of phenomena could never be expected, at any level.

But that had always been absurd -- and now she'd proved it was absurd.

For a moment she thought of phoning Aden, or Francesca -- but Aden wouldn't understand enough to do more than nod politely, and her mother didn't deserve to be woken at this hour.

She got up and paced the tiny bedroom for a while, too excited to remain still. She'd upload a letter to Autoverse Review (total subscription, seventy-three), with the genome of the strain she'd started out with appended as a footnote, so everyone else could try the experiment . . .

She sat down and began composing the letter -- popping up a word processor in the foreground of the workspace -- then decided that was premature; there was still a lot more to be done to form the basis of even a brief report.