Many factors, not just its biological nature, contribute to disease transmission, among which are specific cultural and societal aspects. During the Paleolithic era, early humans lived in mobile communities with little population density, and they subsisted mainly from hunting and gathering. This particular lifestyle, while disadvantageous to psychological and sociological development, afforded these early humans with rudimentary means of disease prevention: little direct human contact, more hygienic living conditions, and constant exposure to diverse environments. However, the advent of the Neolithic era, with the development of farming and domestication, changed the nature of disease transmission among human populations forever.
These Neolithic developments allowed for humans to shift to a more sedentary lifestyle, as food sources could now be grown and cultivated in one spot with agriculture and animal husbandry. However, these developments brought with them significant drawbacks regarding diseases. Humans began to live in communities with higher population densities, which allowed diseases to spread between humans due to the new prevalence of constant, direct contact. Their farm animals shared the same water sources as them, and the concentration of human populations in villages drew rodents and insects en masse. Furthermore, waste disposal remained a low priority for humans, as both human and animal waste build-up allowed for the cultivation and transmission of parasites. Yet, humans survived and continued to evolve more complex communities, eventually creating civilizations with much greater population densities.
A new development in disease transmission came when civilizations began to intermingle with other civilizations. This intermingling led to the end of the geographic isolation of certain diseases, which had no means to transmit to other human populations especially across natural boundaries such as mountains or oceans. The oft-cited example of this evolution in disease transmission is the decimation of Native American populations by European smallpox. Europeans had been exposed to the disease for generations and had grown natural immunity, while the natives had no previous exposure and did not possess the biological means of fighting this disease.