"One in 10 billion trillion" sounds like a very large number, and it's put in italics for emphasis," And the author even asserts it's "irrational" to think rea

"One in 10 billion trillion" sounds like a very large number, and it's put in italics for emphasis," And the author even asserts it's "irrational" to think real-world probabilities are this small! It's easy to construct "unreasonably" small probabilities: take a few small ones and multiply them. If you path-sum all the evolutionary state transitions summing to P(intelligent life|planet), is it a shallow graph with many alternatives (additive probabilities), or a deep graph dominated by long, conjunctive sequences (probabilities multiply)?