Reign of Fire/Fridge
When I first saw this movie, the idea of a species with a single male seemed like evolution had made a pretty serious stuff up (and let's face it, it was there for plot reasons). But later it occurred to me: evolution is adaptive, not predictive. A single male is not actually a weakness if that male is immortal and nothing around can hurt it! Their species had been dominant for millions of years with that approach. It only became a liability when a new species evolved with the intelligence to use tactics to target the male, and develop weapons to fight back...