The idea that correlation does not imply causation is a fundamental caveat in epidemiological research. A classic example involves a hypothetical link between ice cream sales and drownings — instead of increased ice cream consumption causing more people to drown, it's plausible that a third variable, summer weather, is driving up an appetite for ice cream and swimming, and hence opportunities to drown.
But what about correlations involving genes? How can researchers be sure that a particular trait or disease is truly genetically linked, and not caused by something else?
