a behavior that ensures the survival of the fittest. 这种行为能够确保最优秀者生存下来

171. But advances in feeding and flight alone
     但仅靠进食与飞行上的进步
172. were not enough to ensure the future of the birds.
     并不足以确保鸟类有一个光明的未来
173. They also drew on a rather flamboyant ancient behavior,
     它们还依赖于 一种相当引人注目的古老行为
174. a behavior that ensures the survival of the fittest.
     这种行为能够确保最优秀者生存下来
175. Courtship.
     求爱
176. For the flamingos,
     对火烈鸟来说
177. that means a dance-off...
     这就是一场舞蹈比赛

来自《我们星球上的生命 第一季 第六集 Life on Our Planet S01E06 灰烬中重生》第 174 行