Acclimatization in New Zealand
Paleontology can only tell us of the course of evolution, not of its mechanism and causes. It is virtually impossible for the human observer to judge why many changes in animals were favoured by selection—i. e., to assess the selective valency
of differences. “From the extraordinary manner in which European productions have recently spread over New Zealand,” Darwin writes70 “and have seized on places which must have been previously occupied, we may believe, if all the animals of Great Britain were set free in New Zealand, that in the course of time a multitude of British forms would become thoroughly naturalized there and would exterminate many of the natives … Yet the most skilful naturalist, from an examination of the species of the two countries, could not have foreseen the result.” Few of the British mammals now abundant in New Zealand (hedgehog, rabbit, stoat, ferret, for example) had been introduced when Darwin wrote, and the succeeding century of acclimatization has been a rather sad and expensive fulfilment of his prediction.
[Footnote] 70, Origin: 286.