Across from the Optimists sat the Pessimists, who genuflected before graven images of St. Fermi and a host of lesser lightweights. The Pessimists envisioned a lonely universe full of dead rocks and prokaryotic slime. The odds are just too low, they insisted. Too many rogues, too much radiation, too much eccentricity in too many orbits. If the galaxy were alive with intelligence, wouldn't it be here by now?

Equidistant from the two tribes sat the Historians. They didn't have many thoughts on the probable prevalence of intelligent, spacefaring extraterrestrials. But if there are any, they said, they're not just going to be smart. They're going to be mean. The reason wasn't merely Human history, the ongoing succession of greater technologies griding lesser ones beneath their boots. No, the real issue was what tools are for. To the Historians, tools existed for only one reason: to force the universe into unnatural shapes. They treated nature as an enemy, they were by definition a rebellion against the way things were.

Technology is a stunted thing in benign environments, it never thrived in any culture gripped by belief in natural harmony. Why invent fusion reactors if your climate is comfortable, if your food is abundant? Why build fortresses if you have no enemies? Why force change upon a world that poses no threat?

Human civilization had a lot of branches, not so long ago. Even into the twenty-first century, a few isolated branches had barely developed stone tools. Some settled down with agriculture. Others weren't content until they had ended nature itself. Still others had built cities in space. We all rested eventually, though. Each new technology trampled lesser ones, climbed to some complacent asymptote, and stopped. But history never said that everyone had to stop where we did. There could be other, more hellish worlds where the best Human technology would crumble, where the environment was still the enemy.

The threats contained in those environments would not be simple ones. Harsh weather and natural disasters either kill you or they don't, and once conquered — or adapted to — they lose their relevance. No, the only environmental factors that continued to matter were those that fought back, that countered strategies with newer ones, that forced their enemies to scale ever-greater heights just to stay alive. Ultimately, the only enemy that mattered was an intelligent one.