Let’s say my p(intelligent ancestor) is 0.1. Imagine I have a friend, Richard, who disagrees.
No wait, the order of these two things matters. Is P(intelligent ancestor|just my background information) = 0.1 or is P(intelligent ancestor|my background information + the fact that Richard disagrees) = 0.1? I agree that if the latter holds, conservation of expected evidence comes into play and gives the conclusion you assert. But the former doesn’t imply the latter.
No wait, the order of these two things matters. Is P(intelligent ancestor|just my background information) = 0.1 or is P(intelligent ancestor|my background information + the fact that Richard disagrees) = 0.1? I agree that if the latter holds, conservation of expected evidence comes into play and gives the conclusion you assert. But the former doesn’t imply the latter.