It has been argued, most notably by Nathan Cohen, in Health and the Rise of Civilization, that the development of civilization is a function of the increased density of human population. As the number of people increased and open land became scarcer. It was less possible to live merely by foraging. It became necessary to develop a source of food that could sustain a larger number of people. Humans adapted by learning how to domesticate animals and to raise crops. Labour-intensive practices like herding, clearing forests, getting the earth ready for planting, harvesting and preparing food for storage, all required workers and organization.
In larger groups, it was more difficult to make decisions by consensus. Specialist roles emerged for leaders and for experts in hunting game, healing the sick, or deciding when and where to plant next. Manual farm workers were also needed. Towns grew up to support agriculture: local merchants and manufacturers helped the farmers by supplying them with equipment and services they needed to produce crops and helped them distribute their excess products more widely.
Agriculture came with more diseases. Animal germs evolved into germs that affected humans. We began to share diseases with animals: measles from dogs, influenzas from pigs and ducks, colds from horses, and small pox and other viruses from cattle. Today we remain susceptible to diseases from domestic animals. The SARs virus was found to come from bats which infected domestic cats and animals that were being sold in markets in the Quandong province in China.
Permanent settlement and reliance on agriculture had other effects. Human diet became less varied and had an
excessive reliance on starchy monoclutures such as maize, low in proteins, vitamins and minerals. Stunted people are more prone to illness, and poor nutritional levels in turn lead to pellagra, kwashkiorkor, scurvy and other deficiency diseases. (Porter page 5)
The result was that in the change from nomadic foraging to a more sedentary agricultural stage, humans actually became shorter and smaller. More critically the social relations between people began to change. Land owners acquired farm labourers as workers or slaves. Among the earliest written documents in the proto-Elamite tablets from around 3100 B.C. describe the meager rations of gruel and weak beer given to farm workers to keep them just above the starvation level. And so civilization by itself, as Cohen notes, does not guarantee a better diet for all – in the same tablets there are descriptions of the wealth of food choices available to the well off – things like yogurt, cheese and honey. From these earliest times and in many societies there were important distinctions in class levels, types of work and lifestyles. These differences extended to healthcare. There were different classes of patients that more or less correspond to the various social classes. The care given to slaves was no doubt different from that provided for the upper classes. Most medical history is about middle and upper class healthcare, because medical historians typically attach doctors to the higher levels of society. Throughout history these classes shift and their boundaries change: inequalities in patients tend to parallel inequalities in other aspects of society.