December 30, 1922] 



NA TURE 



869 



tion of plants and animals has been a fact to be reckoned 

 with in the evolution of faunas and of humanity. 

 Even in countries where the introduced creatures be- 

 longed to groups identical with, or closely related to, 

 members of the indigenous fauna, and where, on that 

 account, a simple speeding-up of a process already in 

 force might have been expected, the influence of natural- 

 isation on fauna and flora has been profound. It is 

 easy to imagine how much more intense that influence 

 might be in countries where the new-comers belonged 

 to orders of animal and plant life unrepresented in 

 the native fauna and flora, and entered a free field 

 unhampered by the checks which, in the course of ages, 

 had created in the old country a tolerably stable balance 

 of Nature. It is this unusual mingling of the faunas 

 of distinct and widely different zoo - geographical 

 regions that gives special significance to the events in 

 Australia and New Zealand, and has made the 

 attempts of the settlers there a by-word in the history 

 of acclimatisation. 



Another special interest attaches to these areas, 

 however, and adds enormously to the value of this 

 book. In the old countries, lying in the way of the 

 migrations of palaeolithic and neolithic man and his 

 successors, introductions of plants and animals have 

 taken place from time immemorial, with the result 

 that, since the beginnings are lost to view, results can 

 be only dimly envisaged ; but in New Zealand, apart 

 from a few prehistoric Polynesian introductions, 

 almost every beginning has a date, and almost every 

 stage of progress can be measured in terms of years. 

 Mr. Thomson has dealt with the unique opportunity 

 that lay to his hand in the scientific spirit ; he has been 

 chary of broad generalisations, and he has been at 

 endless pains to collect and verify information, much 

 of which in a few years would otherwise have slipped 

 from ken. Consequently his work must be regarded 

 as a standard contribution to the history of ac- 

 climatisation. 



The plan of the book is of the simplest : after a short 

 introduction and historical review, it proceeds to 

 consider each animal and plant introduced to New 

 Zealand, whether or not it has become established, 

 in its order in systematic classification. (The author 

 has overlooked the fact that all his rodents are 

 grouped under the heading " Carnivora.") The mass 

 of material handled can be only roughly gauged by the 

 fact that of mammals and birds alone, 48 of the former 

 have been introduced, of which 25 have become truly 

 feral, and of the latter, 24 out of 150 introduced species 

 are now thoroughly established ; while of plants, more 

 than six hundred species have become " more or less 

 truly wild." 



It is impossible here to follow Mr. Thomson's cata- 



NO. 2774, VOL. I 10] 



logue of events ; even the familiar stories of the ill- 

 starred introductions of the rabbit and its enemies, and 

 of the introduction of humble-bees to fertilise the intro- 

 duced red clover, are filled with new and significant 

 detail ; but let us turn to some of the broad results 

 of this century and a half's intense interference with 

 Nature. 



Great expectations were formed of the probability 

 of seeing the development of new variations and of 

 incipient new species ; but fifty years of close observa- 

 tion lead the author to state that he is " aware of no 

 definite permanent change in any introduced species " 

 (p. 513). The statement does not exhaust the possi- 

 bilities, however ; first, because the time is short — 

 the first animals were introduced in 1773, and most 

 have been in the country for scarcely more than half 

 a century ; secondly, because changes are noticeable — 

 red deer introduced from Forfarshire only fifty years 

 ago, now carry, instead of a former limit of 12, up to 

 20 points on their antlers ; and, thirdly, because the 

 progeny of introduced animals has not been sub- 

 mitted to that minute examination and comparison 

 of cranial and other characters on which racial dis- 

 tinctions are now based. Again, Darwin and Wallace 

 both expected that the wholesale naturalisation of 

 European plants would ultimately exterminate part 

 of the native flora. The author sees no evidence of 

 such a process : " The native vegetation can always 

 hold its own against the introduced " (p. 528) ; " the 

 struggle . . . will result in a limitation of the range of 

 the native species rather than in their actual extermina- 

 tion " (p., 533). But is the conclusion not doubtful, 

 or at any rate premature ? In long-civilised countries, 

 for example, Scotland, it has been shown that there are 

 no bounds to the cumulative effect of man's influence, 

 and that limitation of range is too often but a first 

 step to ultimate, even if long-delayed, extinction. 



Yet many changes have been observed. Introduced 

 trout established new records in size, water-cress grew 

 to a length of twelve to fourteen feet, " with stems as 

 thick as a man's wrist," the common spear thistle 

 formed thickets six to seven feet in height ; even since 

 1868 nine species of birds have disappeared to a great 

 extent or altogether, and many have been driven to the 

 wildernesses ; several species of fish have been ex- 

 terminated by established introductions ; habits have 

 changed — many species have adopted introduced food 

 plants, the Kea parrot supplements its fruit diet with 

 the flesh of living sheep. On the whole, the introduc- 

 tions have done much more harm than good. Of all 

 the birds introduced, the only one against which no 

 complaint has ever been made is the hedge sparrow ; 

 but there must often be difficulty in assessing the 

 balance of good and evil. In one place we are told 



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