His argument is that the unusual history of these people has (subjected) them to unique evolutionary pressures that have resulted in this (paradoxical) state of affairs.
“Large numbers of physicians seem unconcerned with the pain their patients are needlessly and predictably suffering, ” to the extent that it constitutes “systematic patient abuse.”
Those who could afford to live in more pleasant surroundings moved out, and the area became one where the vast majority people lived in extreme poverty, and suffered from appalling sanitary conditions.