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1 Key Factors in Health and Wellness HEALTH AND DISEASE IN HISTORY In early hunter and gatherer societies, with small, scattered populations, humans were unlikely to have been exposed to numerous contagious bacterial and viral diseases that require large, dense populations to spread (such as smallpox). Fur- thermore, the nomadic lifestyle of these early societies would have minimized the possibility of contact with water polluted by human waste and piles of refuse and garbage that might attract disease-carrying insects. Finally, prior to the period of widespread domestication of animals, these peoples were less likely to contract diseases passed on by close contact with dogs, pigs, birds, and cattle, not to men- tion the mice and rats drawn to human dwellings. This is not to say that early humans lived without disease indeed, they still faced a number of diseases caused by eating animals or passed on by worms and lice. The limited population sizes, however, would have limited incidences of infection and death from infectious diseases. As humans began to live together in larger, permanent settlements start- ing around 10,000 b.c.e., they encountered a whole new range of diseases of civi- lization. Living in cities brought humans into closer, regular contact with pathogens and parasites that were spread by contact with domesticated animals or through poor sanitation and fouled water supplies. The larger and denser popula- tions also made it easier for infectious diseases to spread, allowing some (like smallpox and measles) that had previously caused little trouble to emerge and thrive. Furthermore, archaeological evidence indicates that as humans started to live in permanent settlements and rely on agriculture and domesticated animals for food, their diets became less varied and focused on a limited number of staple crops, leading to malnutrition from not getting appropriate nutrients. The changed diets would only further enable the spread of diseases due to weakened immuni- ties. Clearly, the move to civilization brought a trade-off—on the one hand, it may have allowed for increased security, but on the other, it led to an increase in dis- ease. In this context, the need for an effective means of treating disease became even more crucial once humans started to congregate in cities.