The X Files (1993) - 1x11 - Eve

When two fathers on opposite sides of the country are unexplainably murdered at the exact same time in the exact same way, Mulder and Scully find that their eight-year-old daughters are perfect twins and were created in order to continue The Litchfield Experiment, a eugenics project of the 1950's which produced several identical sets of twin boys named Adam and girls named Eve who have heightened strength and intelligence, but are prone to psychotic behaviour.