Dear Doctor (S01E12)

When the Valakians ask for help with a planet-wide plague, Phlox realizes that the problem is genetic: the species is doomed in 200 years unless the immunity of the Menk, a simbiotic people that peacefully share the planet, yields a clue. But Phlox's cure brings up the ethics of interfering in natural selection: the Valakians' extinction would allow the Menk to fulfill signs of further blossoming. A soul-searching Archer agrees with him: the Valakian species is prolonged but not cured, in order to avoid "taking sides." (iTunes)