I agree with CitizenPaul - I think we're alone in sapience/technology, and that possibility is so terrifying that it's never discussed. It's a much smaller burd

I agree with CitizenPaul - I think we're alone in sapience/technology, and that possibility is so terrifying that it's never discussed. It's a much smaller burden if there's tens of millions of other civilizations flying around, but we have 0 evidence after 2 centuries of searching. I think there's some step that's very rare - either bones, or more likely evolving on a planet with wood. It's an easy building material that is also a fuel, and abundant. If we had to make due with rocks when we were just kind of smart apes, we wouldn't have gotten very far.