 For Darwin, the word ‘species’ is indefinable. One reason he thought it was indefinable because he was skeptical of the distinction between species and varieties. For example, in the Origin of Species, he writes, “I look at the term species as one arbitrarily given for the sake of convenience to a set of individuals closely resembling each other, and that it does not essentially differ from the term variety” (1859 [1964], 52). In other words, ‘species’ is indefinable because there is no difference between species and varieties. But why would Darwin think there is no distinction between species and varieties? Darwin offers several reasons (Ereshefsky 2010c). First, Darwin argues that no process distinguishes varieties from species. Second, he contends that any differences drawn between them lie on a seamless continuum and are drawn for pragmatic reasons. Third, Darwin rejects the distinction between varieties and species because it is built on ideas concerning creation rather than natural selection. In what follows we will just look at why Darwin thought there was no process difference between species and varieties.