One by one, natural selection and sexual selection leave the weak and the timid behind.

自然选择和性选择接二连三地淘汰了弱者和胆小鬼。

The other great principle of evolution is sexual selection, and it operates very differently.

进化的另一大原则是性选择，它运作的方式则大相径庭。

Their advanced physiology comes down to one thing...adaptation, the result of both natural and sexual selection.

这些先进的生理机能都能归结为一点，那就是适应能力，这是自然选择和性选择的结果。