Medical education focuses on proximate causes of disease — infection, trauma, cellular regulation, etc. — as opposed to evolutionary understandings of how our traits and responses came to be in the first place. What evolutionary insights are there for clinical medicine?

Medical conditions can occur when there is a mismatch between our evolved bodies and our particular society and environment. This idea challenges some of our notions of disease.

Hardly a day goes by when I don’t see patients with lactose intolerance, allergies, obesity, anxiety, near-sightedness, ADHD, and flu symptoms. The lactase gene spread rapidly in historical populations with dairy husbandry. But 70% of the world’s population is lactose intolerant, all of whom are “normal” in the context of their environments that were, until recently, lactose-free.

Allergies and autoimmune conditions are more common in developed societies where infections occur less frequently. This suggests a mismatch between our evolved immune system and our current environment. Recent evidence suggests that the incidence of autoimmune Crohn’s disease has risen in places where the incidence of gastrointestinal worm infection has fallen.