"If birth collapse occurs nearly every time a civilization goes into decline, which I believe it does, why hasn’t this evolutionary selection process happened before?"
Malaria resistance has been a major evolutionary driver in areas with Malaria, but not so much elsewhere. I recall a story about a spot in England with malaria. Men living there who survived it would often marry several wives in sequence from the surrounding areas. But no resistance was being evolved because importing fresh blood trumped any selection effects that might have been going on.
In the case of Rome and Greece's baby bust, large migrations occurred, swamping any selection effect.
It's hard to say how the modern open-ended experiment on this will go - there is a lot different about the situation than in those classical cases.
"If birth collapse occurs nearly every time a civilization goes into decline, which I believe it does, why hasn’t this evolutionary selection process happened before?"
Malaria resistance has been a major evolutionary driver in areas with Malaria, but not so much elsewhere. I recall a story about a spot in England with malaria. Men living there who survived it would often marry several wives in sequence from the surrounding areas. But no resistance was being evolved because importing fresh blood trumped any selection effects that might have been going on.
In the case of Rome and Greece's baby bust, large migrations occurred, swamping any selection effect.
It's hard to say how the modern open-ended experiment on this will go - there is a lot different about the situation than in those classical cases.
I agree, and intend to do a write up. But it certainly needs explaining.