How do paragraphs 4 - 5 contribute to the development of ideas in the text

“All these changes make good sense. But how does breaking up dice games and streamlining bureaucracy cut murder rates by two-thirds? Many criminologists have taken a broader view, arguing that changes in crime reflect fundamental4 demographic5 and social trends — for example, the decline and stabilization of the crack trade, the aging of the population, and longer prison sentences, which have kept hard-core offenders off the streets. Yet these trends are neither particularly new nor unique to New York City; they don’t account for why the crime rate has dropped so suddenly here and now. Furthermore, whatever good they have done is surely offset, at least in part, by the economic devastation visited on places like Brownsville and East New York in recent years by successive rounds of federal, state, and city social-spending cuts.

[5]It’s not that there is any shortage of explanations, then, for what has happened in New York City. It’s that there is a puzzling gap between the scale of the demographic and policing changes that are supposed to have affected places like the Seven-Five and, on the other hand, the scale of the decrease in crime there. The size of that gap suggests that violent crime doesn’t behave the way we expect it to behave. It suggests that we need a new way of thinking about crime, which is why it may be time to turn to an idea that has begun to attract serious attention in the social sciences: the idea that social problems behave like infectious agents. It may sound odd to talk about the things people do as analogous6 to the diseases they catch. And yet the idea has all kinds of fascinating implications. What if homicide, which we often casually refer to as an epidemic, actually is an epidemic, and moves through populations the way the flu bug does? Would that explain the rise and sudden decline of homicide in Brooklyn North?”