Bruce Charlton has been talking a lot about mutation accumulation, the best introduction of which is probably The Demise of Mouse Utopia.
So this has been percolating around in my brain since it is the sort of thing that changes your view of things quite drastically.
Meanwhile I have this basic idea that Christendom was lobotomized in the 1800s. The revolutionary period meant the destruction of the nobility and the removal of the societal forces that encouraged people to select for intelligence. A different class rose up and took whatever 'traditional' positions that were left- the bureaucrats.
Mutation accumulation adds to the dim picture due to the unequal distribution of live saving technologies.
The children of the wealthy were the first to see a decrease in child mortality. Additionally the wealthy were the first who were able to use plastic surgery, orthodontics, etc...
So the elite classes in the post-revolutionary milieu have accrued far more mutations than the poorer classes. Problems tend to be more obvious in among the poor, but the obviousness in turn tends to discourage people from mating with him or her.
Basic attractiveness and apparent health still count as a decent signal among the poor, while the elites can fake it. Considering the general popularity of C-sections in this country, one could easily imagine three generations of women, each having C-sections, resulting in a great-granddaughter physically unable to give birth normally. One of a myriad of simple examples that would get humans very near the end state found in the mouse utopia experiment.