Throughout history, the impact of diseases on humans has changed as human societies have developed. A. Once advances in medical science resulted in better control or elimination of many infectious diseases, diseases resulting from the modern lifestyle became a major problem. B. Humans today are at risk for contracting both new diseases and old diseases that have reemerged and, in some cases, have become resistant to antibiotics. C. The transition to farming meant that humans had both more contact with one another and with other species that carried disease, leading to disease epidemics. D. In early human history, nomadic groups started encountering diseases when they moved to new environments. E. Infectious diseases have increased steadily in impact and severity from the agricultural revolution through today as a result of increasing contact between human societies. F. During the second epidemiological transition, better public health measures and improved nutrition helped control chronic diseases.