[The Working Man]

Just remember the Black Death. The plague years found many more dying than were born during them. Somehow the Europeans survived that disaster too.

[equalator]

Just like with all great civilizations, 1000 years from now, archeologists will dig up bones in what was America, and they'll say-- "These Americans went to the moon! Here is a typical American":

"According to our fidings--The Typical American was approximately 4 foot tall, was heavy-set and had AIDS."

[Boogieman]

Reproductive strategies automatically adapt to conditions. It’s counterintuitive, but people breed less in times of plenty, and more in the lean times. The 20th century was a time of unprecedented plenty, and I think that is what led to this seemingly suicidal lack of reproduction. All it will take is a bad decade or two, though, and we will be swimming in babies.