Lie #21:
The seventh planet was also a catastrophe planet. I was beginning to realize why we seemed to be alone in the universe - because we are. This planet was a mystery at first that slowly resolved into a horror. The usual causes were missing. There was no world ending planetary collision like Catastrophe Planet # 4. There was no evidence of technology run amok like a petite black hole (Catastrophe Planet #2) or a soupy, unlivable atmosphere (Catastrophe Planet #6). There were just fifteen thousand year old ruins inhabited by large herbivores, abandoned space platforms and habitats, and a decaying satellite system.

It took me almost two decades to realize the horror. What I was seeing was evolution at it's worst and most effective. The large, dumb herbivores were the descendants of the people who built the space stations. Evolution doesn't care about civilization. It cares only about perpetuation of the genetic line, not what that genetic line contains. Intelligence is only conserved as long as it is useful.

At some point about 30 thousand years before, some genetic shift happened and a trait that was more effective than intelligence arose. The people with that trait outbred and outcompeted the smart people. Over time, the population became less intelligent. Their cities fell apart because they didn't know how to keep them running, and eventually they lost everything, even language.

I still have nightmares.