Population density and new sedentary lifestyle provided conditions for epidemic infections of disease, also living in close quarters with domesticated animals made people more susceptible to diseases like the flu Social hierarchies developed reservoirs for disease in impoverished communities living in close quarters with poor sanitation, wealthy elites could also withhold needed resources (water, food) from them Diet concentrated on staple crops reduced diversity of nutrition, especially for lower classes who couldn't afford more more items (imported or scarce)