  Lyell, Herschel, Whewell, Sedgwick and many of Darwin’s contemporaries certainly would not find this a cheering prospect, since they were unrepentant essentialists about  species.[10]  Members of a species possess a ‘type’ established in the original parents, and this type provides ‘fixed limits’ to variability.  Lyell clearly feels this is an empirically verifiable fact—most of chapters 2–4 of Principles Vol. II is devoted to presenting the evidence that such ‘fixed limits’ exist; and after the Origin’s publication this evidence was canvassed again in Fleeming Jenkin’s review.  If this is so, then species extinction is easy to account for—there are fixed limits to a species’ ability to track environmental change.  But a naturalistic account of species origination is more difficult, since there will need to be, in sexually reproducing species, a natural production of a new pair of parents with a new type. On the other hand, to adopt the sort of nominalism that Darwin seems to be advocating in the above quotations has undesirable consequences as well. How are we to formulate objective principles of classification?  What sort of a science of animals and plants will be possible if there are no fixed laws relating their natures to their characteristics and behaviors?  A good deal of chapter 2 of Darwin’s Origin is devoted to convincing the reader that current best practice among botanists and zoologists accepts a natural world organized as he is insisting rather than as his opponents claim: