Revie/ws — Age and Area. 527 



distribution of a species depends, not on any advantage it may be 

 supposed to have over its congeners, as by some ingenious method 

 of seed-dispersal, but solely on the length of time during which the 

 causes of dispersal have operated. Now, since wide dispersal, or 

 its correlative longevity, implies success in life, it follows, on 

 Dr. Willis' reasoning, that success has nothing to do with 

 advantageous or adaptive characters. In other words, all species 

 are equal, and Dr. Willis has no use for Natural Selection. Evolution, 

 according to him, must take place solely through a succession of 

 "mutations" (= saltations), and the direction of evolution must 

 be due to some guiding principle other than the environment. 



Some palaeontologists may welcome this conclusion, others will 

 incline to oppose it. Mrs. E. M. Reid, who contributes from the 

 palseobotanical standpoint a (chapter that in its ease and clarity of 

 style contrasts markedly with the rest of the book, deals with one 

 obvious objection, namely, the extinction of species. The Age and 

 Area hypothesis seems to pass this by too lightly. It assumes that 

 a species originating in, say, Tibet, will go on living and spreading 

 till it has conquered the whole earth. If it at any time become 

 extinct (for even Dr Willis must admit that some species have 

 perished) it will be from " exhaustion of its vitality ". But we know 

 that whole floras and faunas have vanished, and that not merely 

 species and genera, but great systematic groups of animals and plants 

 have been exterminated, some in Palaeozoic, some in Mesozoic times. 

 We see bow at the present day species and genera are exterminated 

 by a change in their physical surroundings, or by the introduction 

 of some actively or passively hostile form of life. We have excellent 

 reasons for our belief that similar changes in the past (a glacial 

 period or the appearance of egg-sucking mammals) have wrought 

 similar havoc. When, then, Mrs. Eeid shows us a progressive 

 extermination of older forms as compared with newer throughout 

 Pliocene times, what right have we to assume that this was due to 

 some inherent defect 1 Must we not rather agree with Lyeil that 

 the fluctuations of the earth's surface provide an efficient cause ? 

 But if this be admitted, the door is again opened to Natural Selection. 

 Dr. Willis confesses that a newly formed species '■' will have a most 

 strenuous struggle for existence, immediately ", but he forgets that 

 this struggle may be renewed by a change in the conditions often of 

 apparently trivial character. 



Dr. Willis also seems to overlook the distinction, on which 

 De Candolle, Lyell, and others insisted, between station and 

 habitation. From this point of view it may be said that adaptation 

 has little to do with geographical extension, but is of chief importance 

 in relation to the precise conditions of life. Diversity of conditions 

 may depend but slightly on locality ; on a single square foot of 

 sea-bottom, of the present or of past ages, we find creatures 

 that live or lived under most different conditions ; and the more 

 we realize those conditions the more we realize the adaptation of 



