1·Birds and mammals invest in quality and not quantity, as opposed to fish and reptiles.
鸟类和哺乳类靠质生存,而非以量取胜，这与鱼类和两栖类不同。
2·And that puts them somewhere between mammals and reptiles, because they still maintain quite a lot of reptilian characteristics that we've lost, for instance they still lay eggs.
鸭嘴兽介于哺乳类与爬行类之间，因为它仍然具备许多爬行动物的特征，如产卵，而这些特征在我们身上已经消失了。
3·Our understanding of monogamy draws heavily on birds rather than mammals.
我们对一夫一妻制的理解主要来自鸟类而非哺乳类。
4·Chickens were included to represent egg-laying animals, such as extinct reptiles, that passed on much of their DNA to the platypus and other mammals in the course of evolution.
鸡被作为卵生动物的代表，一些已经灭绝的爬行动物可能在进化过程中将基因传给了鸭嘴兽和其他哺乳类。
5·The opposing view is that mammals and birds did not become successful and radiate into many different species until after the demise of the dinosaurs.
相对立的观点则认为哺乳类和鸟类在恐龙灭绝之后才成功并演化为各种不同的物种。