If (as is hardly conceivable) the new variety is so perfectly adapted to the conditions that no improvement upon it is possible,—­it will persist, because, though it does not cease to vary, the varieties will be inferior to itself.

If, as is more probable, the new variety is by no means perfectly adapted to its conditions, but only fairly well adapted to them, it will persist, so long as none of the varieties which it throws off are better adapted than itself.

On the other hand, as soon as it varies in a useful way, i.e. when the variation is such as to adapt it more perfectly to its conditions, the fresh variety will tend to supplant the former.

So far from a gradual progress towards perfection forming any necessary part of the Darwinian creed, it appears to us that it is perfectly consistent with indefinite persistence in one state, or with a gradual retrogression.  Suppose, for example, a return of the glacial epoch and a spread of polar climatal conditions over the whole globe.  The operation of natural selection under these circumstances would tend, on the whole, to the weeding out of the higher organisms and the cherishing of the lower forms of life.  Cryptogamic vegetation would have the advantage over Phanerogamic; Hydrozoa over Corals; Crustacea over Insecta, and Amphipoda and Isopoda over the higher Crustacea; Cetaceans and Seals over the Primates; the civilization of the Esquimaux over that of the European.

“5.  Pelzeln has also objected that if the later organisms have proceeded from the earlier, the whole developmental series, from the simplest to the highest, could not now exist; in such a case the simpler organisms must have disappeared.”

To this Professor Koelliker replies, with perfect justice, that the conclusion drawn by Pelzeln does not really follow from Darwin’s premises, and that, if we take the facts of Palaeontology as they stand, they rather support than oppose Darwin’s theory.

“6.  Great weight must be attached to the objection brought forward by Huxley, otherwise a warm supporter of Darwin’s hypothesis, that we know of no varieties which are sterile with one another, as is the rule among sharply distinguished animal forms.

“If Darwin is right, it must be demonstrated that forms may be produced by selection, which, like the present sharply distinguished animal forms, are infertile when coupled with one another, and this has not been done.”

The weight of this objection is obvious; but our ignorance of the conditions of fertility and sterility, the want of carefully conducted experiments extending over long series of years, and the strange anomalies presented by the results of the cross-fertilization of many plants, should all, as Mr. Darwin has urged, be taken into account in considering it.

The seventh objection is that we have already discussed (supra, p. 329).