We have differences correlated not only with one sex, but with that short period when the reproductive system is active, as in the nuptial plumage of many birds, and in the hooked jaws of the male salmon.

我们发现差异不仅与一种性别有关， 而且与生殖系统活跃的短暂时期有关，例如许多鸟类的新婚羽毛， 以及雄性鲑鱼的钩状颚。