I'm also sure Shostak is thinking about probabilities. My point was that we shouldn't necessarily think about the probabilities along a presumed straight-line p

I'm also sure Shostak is thinking about probabilities. My point was that we shouldn't necessarily think about the probabilities along a presumed straight-line path. The logic Shostak is using here begins with a sort of reverse-engineering of how humanity made its progress, followed by an implicit presumption that other advanced civilizations will follow the same path, until such time as they advance beyond us (by way of AI). I don't believe we can confidently say that technology has to progress along the path we walked.