The theory of evolution states that all living beings are the result of a process known as evolution by natural selection. This process occurs whenever genetically influenced variation among a population affects reproductive success. For instance, a genetic mutation that causes greater vulnerability to disease and negatively affects reproductive success will decrease in frequency compared to its alternative allele that causes greater resistance to disease.
It is thought that evolution by natural selection produced the functional design observed in living beings, known as adaptations, and therefore sickness and disease can be explained through a cost v. benefit analysis of physiological function. Understanding evolutionary design helps medical researchers explain phenomena like: infections, injury, intoxication, genetic diseases, aging, allergy, problems during childbirth, cancer and mental disorders.
A well-known example of the application of evolutionary medicine is the study of the evolutionary arms race between the body's defenses and pathogens. Other examples include human populations that have certain disease susceptibilities that arose as compromises allowing their survival. These include, sickle cell anemia protecting against malaria, hemochromatosis protecting against the bubonic plague and cystic fibrosis protecting against typhoid fever.
Certain advocates of evolutionary medicine, such as Loren Cordain and S. Boyd Eaton, have examined the relationship between diet and health by employing evolutionary biology to determine human nutritional requirements and explain the role of diet in the etiology of disease and illness. This approach is based on the premise that metabolic and physiological responses of the body to diet reflect the influence of human evolution and that an understanding of the ancestral human diet can inform contemporary nutritional science.
Proponents of evolutionary medicine, including Loren Cordain and S. Boyd Eaton, have established physical exercise guidelines for health promotion and disease prevention, recommending the adoption of a physically active lifestyle similar to that of ancestral hunter-gatherers. Advocates argue that modern humans are adapted to a life of strenuous physical activity. Hunter-gatherers typically walk and run 5 to 10 miles per day in search of food, and, in so doing, they basically cross-train, performing aerobic, resistance, and flexibility exercises. Days of intense physical activity are followed by days of recovery. Their survival requires them to be extremely physically active.