Evolution is defined as a gradual process in which organisms become better adapted to their environment through gradual changes that occur from generation to generation. Throughout the history of life, the human species has evolved to become better adapted to the environment. All changes ultimately result from mutations that occur at the gene level. Pathogens such as bacteria or viruses that live inside our cells have had a major influence on our evolution (Parks, Panelli & Weinstein, 2003). Pathogens have affected our evolution in two major ways, which I will focus on: antibiotic resistance and virulence. Virulence also changed with respect to reproductive patterns and the establishment of a higher fitness rate. In addition to pathogens, the human body has evolved processes in which cells are better protected (Parks, Panelli & Weinstein, 2003). These processes are called defense mechanisms or the immune system. Due to the continued evolution of human health and medicine, evolution has been selective in providing the human species with a higher level of fitness. At the cellular level, genes are made up of DNA, which is the genetic blueprint for growth and development. When DNA is replicated and undergoes cell division, errors, called mutations, can occur. After several generations of offspring have been produced, the mutations will eventually change enough to show a new distinctive trait such as a particular disease or disorder (Ovchinnikov, Rubin & Swergold, 2002). If the same genes are passed down and carry the characteristics of a particular disorder, then the fitness of the host will be reduced due to the impact of a certain disease. An example would be cystic fibrosis, which develops......middle of article......ca, 88(10), 4270-4274.Madigan, M. and Martinko, J. (2006) . Brock biology of microorganisms. (11 ed.). New York, NY. McDade, T. (2005). Ecologies of human immune function. Annual Review of Anthropology, 34, 495-521. Ovchinnikov, I., Rubin, A. and Swergold, G. (2002). Tracing the lines of human evolution. Proceedings of the National Academy of Sciences of the United States of America, 99(16), 10522-10527. Parkes, M., Panelli, R. and Weinstein, P. (2003). Converging paradigms for environmental health theory and practice. Environmental Health Perspectives, 111(5), 669-675. Futuyma, D. (2009). Evolution. (2 ed., pp. 421-424). Sunderland, MA: Sinauer Associates, Inc. Willard, H., Angrist, M., & Ginsburg, G. (2005). Genomic medicine: genetic variation and its impact on the future of health care. Philosophical Transactions: Biological Sciences, 360(1460), 1543-1550.