And the next step on the evolutionary ladder.

是进化的更高级。

Look, are you working your way down the evolutionary ladder?

你怎么越做档次越低呢？

Before lessons can be drawn from critters perched on the lower rungs of the evolutionary ladder, their behaviour must first be understood.

因为必须首先理解这些动物的行为，人们才能借鉴，而由于这些动物处于进化阶梯的较低位置，（人们并不容易理解）。