Larry Niven - The Ringworld Engineers

Phssthpok came tracking a Pak colony ship that had reached Earth more than two million years earlier.

The Pak were in a constant state of war. Previous colonies to nearby worlds in the galactic core had always been overrun by subsequent waves of ships. Perhaps that was the reason this ship had come so far.

The colony was large and well-equipped, and guided by beings tougher and smarter than humans. It had failed nonetheless. Tree-of-life grew in Earth’s soil, but the virus didn’t. The protectors had died out, leaving a lost population of Pak breeders to fend for themselves… and leaving records of a cry for help that had crossed thirty thousand light-years to the Pak home world.

Phssthpok found those records in an ancient Pak library. And Phssthpok crossed thirty thousand light-years, all alone in a slower-than-light craft, seeking Sol system. The resources that built that craft, in knowledge and minds and materials, were resources Phssthpok had conquered and held by war. His cargo pod was jammed with tree-of-life roots and seeds, and bags of thallium oxide. His own research had discovered the need for that unusual soil additive.

It might have occurred to him that the breeders would mutate.

Among the Pak a mutant stood no chance. If the children smelled wrong to their protector forefathers, they were killed. On Earth — perhaps Phssthpok counted on a lower mutation rate, this far from the savage cosmic-ray density among the core suns. Perhaps he took his chances.

The breeders had mutated. By Phssthpok’s time they showed little resemblance to the Pak breeder — barring certain changes at middle age, when the production of eggs stopped in females, and when both sexes showed wrinkling of skin, lost teeth, swelling of joints, and a restlessness and dissatisfaction that was all that remained of the hunger for tree-of-life. Later in life, heart attacks would result from the lack of the second heart.

Phssthpok learned none of this. The rescuer died almost painlessly, with no more than a suspicion that those he intended to rescue had become monsters, and had no need of him at all.

Such was the tale that Jack Brennan told to United Nations representatives before his disappearance. But Phssthpok was dead by then, and Jack Brennan’s testimony was doubtful. He had eaten tree-of-life. He had become a monster; his braincase in particular was expanded and distorted. Perhaps he had become mad too.

It was as if a load of spinach noodles had been spilled all over this rocky area. Strips of greenery, fuzzy to the touch, hugged the ground in places where dirt had packed itself between the boulders. Clouds of insects buzzed around their ankles, staying within inches of the ground.

“Pak protectors,” said Louis. “That’s what I thought, but I’ve been having trouble making myself believe it.”

Chmeee said, “The vacuum suits and the Grass Giant’s armor show their shape: humanoid, but with enlarged joints and a face pushed forward. There is more proof. We’ve met so many hominids, all different. They had to be derived from a common ancestor: your own ancestor, the Pak breeder.”

“Sure. It’d also tell us how Prill died.”

“Does it?”

“Boosterspice was tailored for the metabolism of Homo sapiens. Halrloprillalar couldn’t use it. She had her own longevity drug, and it could be used by a number of species. It struck me that Prill’s people might have made it from tree-of-life.”

“Why?”

“Well, the protectors lived thousands of years. Some factor of tree-of-life, or a subcritical dose of it, might trigger just enough of the change to do that for a hominid. And the Hindmost says Prill’s supply was stolen.”

Chmeee was nodding. “I remember. One of your asteroid mining craft boarded the abandoned Pak spacecraft. The oldest man in the crew smelled tree-of-life and went mad. He ate beyond the capacity of his belly, and died. His crewmates could not restrain him.”

“Yah. Now, is it too much to expect that the same thing happened to some UN lab assistant? Prill walks into the UN building carrying a flask of Ringworld longevity drug. The UN wants a sample. A kid barely too young for his first dose of boosterspice — forty, forty-five — opens the flask. He’s got the eyedropper all ready. Then he gets a whiff. He drinks it all.”

Chmeee’s tail lashed air. “I would not go so far as to say that I liked Halrloprillalar. Still, she was an ally.”

“I liked her.”

The hot wind blew around them, filled with dust. Louis felt harried. They wouldn’t get another chance to talk in privacy. The probe that relayed signals to and from Needle would soon be too high up the Arch for this kind of trick to work.

“Can you think like a Pak for me, Chmeee?”

“I can try.”

“They put maps all over the Great Oceans. Instead of mapping Kzin and Down and Mars and Jinx, can you tell me why Pak protectors wouldn’t just exterminate the kzinti and Grogs and martians and bandersnatchi?”

“Uurrr. Why not? The Pak would not flinch at exterminating alien species, according to Brennan.”

Chmeee paced as he mulled the problem. He said, “Perhaps they expected to be followed. What if they lost a war; what if they expected the winners to come hunting them? To the Pak, a dozen burnt-out worlds within a dozen light-years of one another might indicate the presence of Pak.”

“Mmm… maybe. Now tell me why they’d build a Ringworld in the first place. How the futz did they expect to defend it?”

“I would not attempt to defend a structure so vulnerable. Perhaps we will learn. I have also wondered why Pak would come to this region of space in the first place. Coincidence?”

“No! Too far.”

“Well?”

“Oh… we can guess. Suppose a lot of Pak wanted to run as fast and as far as they could. Again, say they lost a war. Got kicked off the Pak world. Well, there was one safe route out into the galactic arms, and it was mapped. The first expedition, the one that settled Earth, got to Sol system without running into any danger they couldn’t handle. They sent back directions. So the losers followed them. Then they set up shop a good safe distance from Sol system.”

Chmeee mulled that. Presently he said, “However they came here, the Pak were intelligent and warlike xenophobes. That has implications. The weapon that vaporized half of Liar , the weapon you and Teela persisted in calling a meteor defense, was almost certainly programmed to fire on invading ships. It will fire on Hot Needle of Inquiry or the lander, given the chance. My second point is that the Hindmost must not learn who built the Ringworld.”

Louis shook his head. “They must be long gone. According to Brennan, a protector’s only motivation is to protect his descendants. They wouldn’t have let mutations develop. They’d never have let the Ringworld start sliding into the sun.”

“Louis—”

“In fact they must have been gone hundreds of thousands of years. Look at the variety of hominids we’ve found.”

“I would say millions of years. They must have departed soon after the first ship called for help, and died soon after completing the structure. How else would all of these varieties have had time to develop? But—”

“Chmeee, look: suppose they finished the Ringworld a mere half million years ago. Give the breeders a quarter of a million years to spread out, with the protectors fighting no wars because the territory’s virtually unlimited. Then let the protectors die off.”

“From what?”

“Insufficient data.”

“Accepted. Well?”

“Let the protectors die off a quarter of a million years ago. Give the breeders a tenth the time it took humans to evolve on Earth. A tenth of the time, and a lot of nice gaps in the ecology because the protectors didn’t bring anything to prey on the breeders, and a base population in the trillions .