Evolutionary reasoning in medicine

An editorial in the latest issue of PLoS Biology speaks of the need for evolutionary based reasoning in medical education .

Does Medicine without Evolution Make Sense?
Catriona J. MacCallum

The title is a take from Dobzhansky's quote "Nothing in biology makes sense except in the light of evolution"

The interesting thing from this editorial was some of the reasons why evolutionary reasoning is not taught in medical schools. For example:

"One reason that evolution doesn't figure prominently in the medical community is that although it makes sense to have evolution taught as part of medicine, that doesn't make it essential. As explained at a meeting on evolution and medicine I recently attended in York, United Kingdom (the Society for the Study of Human Biology and the Biosocial Society's 2006 symposium, “Medicine and Evolution”), medicine is primarily focused on problem-solving and proximate causation, and ultimate explanations can seem irrelevant to clinical practice. Crudely put, does a mechanic need to understand the origins, history, and technological advances that have gone into the modern motor vehicle in order to fix it?"

I do not understand the reasoning behind the last sentence in this paragraph at all:

"Many diet-related conditions that typify industrialized populations—e.g., obesity, hypertension, and tooth decay—have been explained as resulting from an evolutionary mismatch between our over-refined, fat-filled contemporary diet and the environment to which humans were once ideally adapted. Sarah Elton (Hull York Medical School, UK) cautioned that while this analogy (the “environment of evolutionary adaptedness”) has been useful as a research tool and has led to public health campaigns for better diets (more seeds, nuts, fish oil, etc.), recreating such a typical “Stone Age diet” as a benchmark can be misleading. Human ecology in the past was at least as variable as human (and other primate) ecology is today."

...what does "variable" have to do with it?