Editors' introduction

When examined in detail, cities are so highly diverse and continually changing that grouping them for comparison to rural settlements requires their essential diversity to be ignored. Each city represents one possible position along a continuum of change and diversification. Although the current configuration of each city has developed from its own individual history, this chapter shows that certain commonalties have also existed. Before the nineteenth century many large cities were built on a trade economy, but, by the middle of that century, cities also grew as suppliers of energy, and as centers of manufacturing. The transition involved tremendous migration from the countryside, and marked increases in population sizes and densities of cities took place. There was a concomitant increase in infectious disease, undernutrition, and the deterioration of human health and well-being. However, by the late nineteenth and early twentieth centuries, government legislation had played a crucial role in improving conditions of sanitation, housing, labor and food supply. The role of government continues to be important in regulating urban hazards to health from such factors as pollutants and traffic. As McMichael shows, the health and biology of urban residents can be traced to direct influences from urban factors such as transportation, violence, climate and activity.