Perhaps the earliest and simplest definition of evolutionary medicine (then called just Darwinian medicine) was:
"the enterprise of trying to find evolutionary explanations for vulnerabilities to disease"
(See: 'What is Darwinian Medicine?' within this site.)
This is still a good basic definition. However, the field has developed and the following is a fuller - although still concise - definition:
Evolutionary medicine is an interdisciplinary field at the intersection of evolutionary biology, medicine, public health, and other health professions. It applies the basic science of evolutionary biology to improve the health of individuals, and it pursues studies of medical issues that can advance basic science.
Evolutionary medicine has important clinical applications, but it is not a method of practice and it does not make treatment recommendations. Instead, it provides a heuristic that generates hypotheses whose tests, along with controlled clinical studies, provide evidence-based clinical recommendations.
While evolution suggests new ways of viewing medical phenomena, it complements more conventional approaches – it does not displace them. It includes explanations for our vulnerability to diseases as well as medical applications of evolutionary genetics, molecular phylogenetics, and evolutionary epidemiology.
While it has already proven helpful in understanding the evolution of antibiotic resistance, virulence, cancer, and autoimmune diseases, the field is in a phase of rapid growth that makes it difficult to predict where its future contributions will be greatest. Much will depend on how quickly we can provide health professionals with education about evolutionary biology that is comparable to that they receive about other basic medical sciences.
(From The Evolution, Medicine, and Public Health Foundation.)