If natural selection eliminates harmful genes, why do so many disease-causing variants persist in the human population? Sickle cell trait protects against malaria. CFTR mutations linked to cystic fibrosis may have conferred resistance to cholera. Certain variants associated with depression and anxiety were probably adaptive in high-threat ancestral environments. The question evolutionary medicine asks is not “why do these genes exist?” but “what did they do for our ancestors that made them worth keeping?”
Sharon Moalem and the “Survival of the Sickest” framework
Physician and geneticist Sharon Moalem popularised this framework in his 2007 book Survival of the Sickest. The central insight: many genetic variants we now associate with disease were historically advantageous — either protecting against infectious disease, enabling survival in specific climates, or providing a metabolic edge in environments very different from ours.
Haemochromatosis (iron overload) is a striking example. In medieval Europe, excess iron storage may have been protective against plague and other bacterial infections that require iron to replicate. The gene persisted because it conferred survival advantage in a specific historical context. In the modern world, where plague is rare but iron-rich processed diets are ubiquitous, the same variant causes organ damage.
The mismatch principle applied to genetics
This is evolutionary mismatch at the genetic level. The variant isn’t “bad” — it’s a solution to a problem that no longer exists, operating in an environment it was never designed for. The same logic applies to the thrifty gene in type 2 diabetes, to anxiety-linked variants that were adaptive in predator-rich environments, and to inflammatory variants that protected against infection but now contribute to autoimmune disease.
What this means at OQ
Understanding that a symptom or condition has an evolutionary origin — that it represents an ancient solution in a new context — changes the therapeutic relationship. We stop looking for what’s broken and start asking what the body was trying to do. At OQ, this perspective applies to every presentation we encounter: from chronic pain to hormonal disruption to immune dysfunction. The body is not the enemy.
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