 From this model of human selection working on small natural variations to produce the domestic forms, Darwin then developed in the second chapter the implications of “natural” variation, delaying discussion of the concept of natural selection until chapter four. The focus of the second chapter introduces another important issue. Here he extends the discussion of variation developed in chapter one into an attack on the traditional “Linnaean” understanding of classification as a sorting out of species by means of essential defining properties. It is in this chapter that Darwin most explicitly develops his own position on the nature of organic species in relation to his theory of descent. It is also here that he sets forth the ingredients for his attack on species “essentialism”.