How strange is it if the sea life evolves to fit the new conditions?

How strange, if new life evolves capable of living on the garbage?

"That happened on Earth once," said Louis Wu. "A yeast that could eat polyethyline. It was eating the plastic bags off the supermarket shelves. It's dead now. We had to give up polyethyline."

Consider ten such worlds.

Bacteria evolved to eat zinc compounds, plastics, paints, wiring insulation, fresh rubbish, and rubbish thousands of years obsolete. It would not have mattered but for the ramships.

The ramships came routinely to the old worlds, seeking forms of life that had been forgotten or that had not adapted to the Ringworld. They brought back other things: souvenirs, objets d'art which had been forgotten or merely postponed. Many museums were still being transferred, one incredibly valuable piece at a time.

One of the ramships brought back a mold capable of breaking down the structure of a room-temperature superconductor much used in sophisticated machinery.

The mold worked slowly. It was young and primitive and, in the beginning, easily killed. Variations may have been brought to the Ringworld several times by several ships, until one variation finally took hold.

Because it did work slowly, it did not ruin the ramship, until long after the ramship had landed. It did not destroy the spaceport's cziltang brone until crewmen and spaceport workmen had carried it inside. It did not get into the power beam receivers until the shuttles that traveled through the electromagnetic cannon on the rim wall had carried it everywhere on the Ringworld.

"Power beam receivers?"

"Power is generated on the shadow squares by thermoelectricity, then beamed to the Ringworld. Presumably the beam, too, is fail-safe. We did not detect it coming in. It must have shut itself down when the receivers failed."

"Surely," said Speaker, "one could make a different superconductor. We know of two basic molecular structures, each with many variations for different temperature ranges."

"There are at least four basic structures," Nessus corrected him. "You are quite right, the Ringworld should have survived the Fall of the Cities. A younger, more vigorous society would have. But consider the difficulties they faced.

"Much of their leadership was dead, killed in falling buildings when the power failed.

"Without power they could do little experimenting to find other superconductors. Stored power was generally confiscated for the personal use of men with political power, or was used to run enclaves of civilization in the hope that someone else was doing something about the emergency. The fusion drives of the ramships were unavailable, as the cziltang brones used superconductors. Men who might have accomplished something could not meet; the computer that ran the electromagnetic cannon was dead, and the cannon itself had no power."

Louis said, "For want of a nail, the kingdom fell."

"I know the story. It is not strictly applicable," said Nessus. "Something could have been done. There was power to condense liquid helium. With the power beams off, the repair of a power receiver would have been useless; but a cziltang brone could have been adapted to a metal superconductor cooled by liquid helium. A cziltang brone would have given access to spaceports. Ships might have flown to the shadow squares, reopened the power beams so that other liquid-helium-cooled superconductors could be adapted to the power beam receivers.

"But all this would have required stored power. The power was used to light street lamps, or to support the remaining floating buildings, or to cook meals and freeze foods! And so the Ringworld fell."

"And so did we," said Louis Wu.

"Yes. We were lucky to run across Halrloprillalar. She has saved us a needless journey. There is no longer any need to continue toward the rim wall."

Louis's head throbbed once, hard. He was going to have a headache.

"Lucky," said Speaker-To-Animals. "Indeed. If this is luck, why am I not joyful? We have lost our goal, our last meager hope of escape. Our vehicles are ruined. One of our party is missing in this maze of city."

"Dead," said Louis. When they looked at him without comprehension, he pointed into the dusk. Teela's flycycle was obvious enough, marked by one of four sets of headlamps.

He said, "We'll have to make our own luck from now on."

"Yes. You will remember, Louis, that Teela's luck is sporadic. It had to be. Else she would not have been aboard the Liar. Else we would not have crashed." The puppeteer paused, then added, "My sympathies, Louis."

"She will be missed," Speaker rumbled.

Louis nodded. It seemed he should be feeling more. But the incident in the Eye storm had somehow altered his feelings for Teela. She had seemed, for that time, less human than Speaker or Nessus. She was myth. The aliens were real.

"We must find a new goal," said Speaker-To-Animals. "We need a way to take the Liar back to space. I confess I have no ideas at all."

"I do," Louis said.

Speaker seemed startled. "Already?"

"I want to think about it some more. I'm not sure it's even sane, let alone workable. In any case, we're going to need a vehicle. Let's think about that."

"A sled, perhaps. We can use the remaining flycycle to tow it. A big sled, perhaps the wall of a building."

"We can better that. I am convinced that I can persuade Halrloprillalar to guide me through the machinery that lifts this building. We may find that the building itself can become our vehicle."

"Try that," said Louis.

"And you?"

"Give me time."

The core of the building was all machinery. Some was lifting machinery; some ran the air conditioning and the water condensers and the water-taps; and one insulated section was part of the electromagnetic trap generators. Nessus worked. Louis and Prill stood by, awkwardly ignoring one another.

Speaker was still in prison. Prill had refused to let him up.

"She is afraid of you," Nessus had said. "We could press the point, no doubt. We could put you aboard one of the flycycles. If I refused to board until you were on the platform, she would have to lift you."

"She might lift me halfway to the ceiling, then drop me. No."

But she had taken Louis.

He studied her while pretending to ignore her. Her mouth was narrow, virtually lipless. Her nose was small and straight and narrow. She had no eyebrows.

Small wonder if she seemed to have no expression. Her face seemed little more than markings on a wigmaker's dummy.

After two hours of work, Nessus pulled his heads out of an access panel. "I cannot give us motive power. The lift fields will do no more than lift us. But I have freed a correcting mechanism designed to keep us over one spot. The building is now at the mercy of the winds."

Louis grinned. "Or a tow. Tie a line to your flycycle and pull the building behind you."

"There is no need. The flycycle uses a reactionless thruster. We can keep it within the building."

"You thought of it first, hmm? But that thruster's awfully powerful. If the 'cycle tore itself loose in here -"

"Yesss -" The puppeteer turned to Prill and spoke slowly and at length in the language of the Ringworld gods. Presently he said to Louis, "There is a supply of electrosetting plastic. We can embed the flycycle in plastic, leaving only the controls exposed."

"Isn't that a little drastic?"

"Louis, if the flycycle tore itself loose, I could be hurt."

"Well … maybe. Can you land the building when you need to?"

"Yes, I have altitude control."

"Then we don't need a scout vehicle. Okay, we'll do it."