The key text that inspires Evolutionary Medicine - and evolutionary science in general - is, of course Darwin's 'On The Origin of Species By Means Of Natural Selection'. However, from time to time, one comes across other work from that era which may prove informative about ideas and ways of thinking that are no longer prevalent today. Some may even find such work to be philosophically inspiring.
Although it was not the intention of its originators, evolutionary medicine has become divisible into two separate branches. These may be described as Clinical Evolutionary Medicine and Anthropological Evolutionary Medicine. The former branch is how evolutionary (then Darwinian) medicine was originally envisaged: as a discipline that offers evolutionary explanations for medical conditions and from those explanations offers insights leading to more successful treatments. Anthropological Evolutionary Medicine is a branch that has emerged out of the interest shown by anthropologists who have recognised that medical conditions (and conditions of medical interest) differ in people of different geographical origin.
There is another quite subtle distinction between the two branches that can be made. The ultimate object of Clinical Evolutionary Medicine is the individual - the patient - whereas the object of Anthropological Evolutionary Medicine to understand people - or perhaps more precisely, peoples. In order to achieve this, both branches may begin with population-based data but the ultimate end is not the same. (To that end, the findings of Anthropological Evolutionary Medicine may feed into the Clinical Evolutionary Medicine. Thus, the two branches should not be seen as mutually exclusive.)
Modern science deals with populations rather than individuals. In medicine the opposite is largely the case. However, if one looks at some of the work from the nineteenth century that forms a basis for modern evolutionary theory, the individual was more prominent. Spencer's famous quote about the 'survival of the fittest' - although nowadays often used in population terms - was originally referred to individuals.
The Complete Works of Charles Darwin
On The Origin Of Species (Wikipedia page)
T.H. Huxley (1881) - The Connection of the Biological Sciences with Medicine
This file includes hyperlinks and annotations by Steve Lewis.
Herbert Spencer (1868) - The Principles of Biology
(See page 444 for the phrase "survival of the fittest" in its original context.)