Anthropology, 210 (Agriculture and Diseases)

Before agriculture and the domestication of consumable animals, humans were nomadic groups moving between locations, foraging and hunting for food.  As agriculture developed, tribes were able to create small settlements and create more advanced social structures.  Some settlements were in naturally fertile areas while others were adapted using irrigation techniques.  Developments in agriculture and animal raising made it possible for larger populations to congregate in a single location.  Close quarters, waste build up, proximity to animals, and enlivened trade made populations susceptible to disease.

Cramped space makes disease easier to transmute from person to person, making the impact larger than a smaller population over a faster amount of time before people can have the chance to develop immunities.  With more people and animals producing waste faster than can be properly dealt with, some animal borne diseases transfered to humans.  Animals also carried parasites which compounded in moist geography and areas that were developed with irrigation.

Large production of resources and established settlements made trade more common and easier even across broad distances.  Remaining nomadic groups would travel from settlement to settlement with not only goods but also carried diseases with them between populations.  This pattern had many different effects, including weeding out the weak, crippling a settlement against invasions, or even completely wiping them out.