"The autotrophs developed in a kind of Eden, where predation didn't exist. They developed technology more as an outgrowth of their own bodies than as a cultural phenomenon. Imagine their shock when they began to visit other worlds and discovered that creatures who actually ate one another were dominant nearly everywhere.

"We've met the autotrophs. But they won't speak to us. To them, we are the worst possible moral abomination, right down to the cellular level.

"Then there's the solitaires. They're individual creatures, we know that. Each one has built a starship around itself and they travel all over the galaxy. But they don't have the concept of language at all; they're solopsists. Since we haven't even met one, we can only theorize about how they developed technology; I think they reproduce by budding and the new bud takes away the knowledge of its elder. But who knows?

"And there's the sylphs, who are incredibly dangerous. We set up colonies on six sylph worlds before we even knew they existed. A biologist on one of the colonies made the discovery that every form of life on her planet had identical DNA— from the giant fern forests to sea slugs at the bottom of the ocean, it was one species, just expressing different genes to become different life-forms. And even the plants had nervous systems. What's more, the colonists had all reported various levels of radio and electronic interference on these worlds. It turns out the sylphs communicate constantly— it's a global network that passes experiential information back and forth. By the time we realized this, a good ten percent of the colonists themselves were sylphs— changelings, replaced in the womb by mimics.

"After an initial panic we realized the sylphs weren't attacking, they were just doing what they do— adapting to a new feature of the environment, in this case us. The changelings didn't even know they were sylphs— their human consciousness was completely separate from the underlying sylph mind.

"Discovering this, we made the fatal mistake: We tried to communicate with them.

"The result," said Herat sadly, "was the extermination of a colony of twenty-five thousand people and the subsequent cauterization of the continent they'd lived on by our navy. It turns out that to the sylphs, the highest ideal is adaptation. To them, the notion of adapting your environment to suit you is horrifying.

"They happily cohabited with us as long as they saw us as just another feature of the local environment. When they realized we were conscious beings like themselves, they were so outraged that they moved to destroy us. We had to wipe out one entire sylph culture in order to prevent the information spreading to the others. The sylphs have FTL and they're incredibly powerful. We're now in the midst of pulling our colonies off their worlds— slowly and carefully."

Rue took off her sunglasses and rubbed her eyes. "That's awful."

"Well, the R.E. became a lot more cautious after that. About eight years ago, I was assigned to explore the various ruins we'd found and try to come up with a general pattern for the rise and fall of galactic civilizations."

"Really?" She seemed fascinated by that idea. "Is that when you hired Mike?" She turned her dark eyes in his direction.

"Shortly after," said Herat. "We visited hundreds of worlds and we did find a pattern. But we resisted accepting it, until we visited a place called Dis and were hit over the head with it." He smiled ironically.

"Go on," said Salas. "I've heard of Dis— what's it like?"

"Dis is a rectangular piece of woven fullerene, ten meters thick, four hundred kilometers wide, and five hundred long. Three billion years ago, it was part of a ring-shaped orbital structure almost two thousand kilometers in diameter. It had two-hundred kilometer high walls on the edges of the ring to keep atmosphere in and it rotated to provide gravity. At some time after its abandonment it must have been hit by an asteroid, which tore it apart. The part we found is in a highly elliptical orbit around a white dwarf star that was once a G-class sun. This sun long ago swelled up, swallowed its planets, and shrank again. Dis is the only legacy of a magnificent species three billion years old.

"Most of the soil and structures that were on the inside surface of the Dis ring were knocked off it in the catastrophe, but we found one nearly intact city and thousands of kilometers of subsurface tunnels. They left records and we were able to piece together a little of their history.

"They wanted their civilization to last forever— that's the one thing we do know about them. They built for the ages in everything they did. The evidence is that they did last a very long time— maybe eighty million years. But early on, they discovered a disquieting truth we are only just learning ourselves. It is this: Sentience and toolmaking abilities are powerful ways for a species to move into a new ecological niche. But in the long run, sentient, toolmaking beings are never the fittest species for a given niche. What I mean is, if you need tools to survive, you're not well fitted to your environment. And if you no longer need to use tools, you'll eventually lose the capacity to create them. It doesn't matter how smart you are, or how well you plan: Over the longest of the long term, millions of years, species that have evolved to be comfortable in a particular environment will always win out. And by definition, a species that's well fitted to a given environment is one that doesn't need tools to survive in it.

"Look at crocodiles. Humans might move into their environment— underwater in swamps. We might devise all kinds of sophisticated devices to help us live there, or artificially keep the swamp drained. But do you really think that, over thousands or millions of years, there won't be political uprisings? System failures? Religious wars? Mad bombers? The instant something perturbs the social system that's needed to support the technology, the crocodiles will take over again, because all they have to do to survive is swim and eat.

"It's the same with consciousness. We know now that it evolves to enable a species to deal with unforeseen situations. By definition, anything we've mastered becomes instinctive. Walking is not something we have to consciously think about, right? Well, what about physics, chemistry, social engineering? If we have to think about them, we haven't mastered them— they are still troublesome to us. A species that succeeds in really mastering something like physics has no more need to be conscious of it. Quantum mechanics becomes an instinct, the way ballistics already is for us. Originally, we must have had to put a lot of thought into throwing things like rocks or spears. We eventually evolved to be able to throw without thinking— and that is a sign of things to come. Some day, we'll become like the people of Dis, able to maintain a technological infrastructure without needing to think about it. Without needing to think, at all…

"The builders of Dis faced a dilemma: The best way to survive in the long run on any world they colonized was to adapt yourself to the environment. The best survivors would be those who no longer needed technology to get by. They tried to outlaw such alterations, but how do you do such a thing for the long term without suppressing the scientific knowledge that makes it possible? Over tens or thousands of millennia, you can only do this by suppressing all technological development, because technologies intertwine. This tactic results in the same spiral into nontechnological life. So inevitably, subspecies appeared that were better survivors in a given locale, because they didn't need technology in that locale. This happened every time, on all their worlds.

"The inhabitants of Dis had studied previous starfaring species. The records are hard to decipher, but I found evidence that all previous galactic civilizations had succumbed to the same internal contradictions. The Dis-builders tried to avoid their fate, but over the ages they were replaced on all their worlds by fitter offspring. These descendents had no need for tools, for culture, for historical records. They and their environment were one. The conscious, spacefaring species could always come back and take over easily from them. But given enough time… and time always passes… the same end result would occur. They would be replaced again. And so they saw that their very strength, the highest attainments they as a species had achieved, contained the seeds of their downfall.