The 1920s saw the advent of expensive and clunky contraception: condoms and STD treatments (Listerine mouthwash is a reformulated gonorrhea treatment. Mucous membranes are mucous membranes regardless of location.) and that information was lost in a general tech boom. The 70s and 80s saw sperm donation and host mothering take off. The S&L boom and 1994-2006 housing bubble followed. Increased selection, fewer adult children per mother, certainly should trip circuits in the primitive brain so that a great depression results. The goal being to get rid of the idiots that caused the selection pressure to go up.