Civilization leads to epidemics because of proximity. When a civilization flourishes, more people are living closer together in fixed abodes. They also gather in public places more frequently, and are more likely to travel and spread disease. Civilization implies job and class differentiation, which means that different people have exposure to different kinds of bacteria and viruses. Once those people live close to one another or meet in groups, it does not take much to create an epidemic. Civilization also frequently implies public water and sewage systems. These are a great idea, but early civilizations had no clue about treating water systems to prevent epidemics, so everyone used the same water, and if there was something wrong with it, an epidemic was inevitable.
The swine flu, which has an official name that escapes me right now, is a good example of how an epidemic spreads in civilization. If you recall, Mexico's first official act upon learning of the epidemic was to close restaurants, schools, and other public gathering places. In an "uncivilized" situation, people do not gather in this way, and epidemics are less likely. Nor do they live as close to one another, and so are less likely to spread disease.
Civilization leads to epidemics in three ways>
- Civilization leads to larger group of people living together. Thus the population density increases, which in turn, increases the incidence of spread of infection.
- Civilization also encourages trade between people from different geographic regions. This also aids in spread of infection.
- Civilization has involved large scale domestication of animals. This increases the incidence of spread of diseases from animals. The swine flue currently raging through out the world currently is a live example of epidemics caused by animals.
While civilization, thus causes greater spread of epidemics, it is worth noting that people living in civilized societies develop, over a period, high level of immunity from many such diseases. But when these people come in contact with other communities, it can have a disastrous effect on them. Something of this kind happened when Europeans settled in America, their presence caused large scale epidemics among the native people who did didn't have immunity from many diseases introduced among them by foreigner settlers. Diamond argues. this weakened the native population and thus enabled a small number of Europeans to dominate the local people.