114 Review of Darwin 



tion of all the effects of external conditions of existence to these 

 supposed causes of change. We could fill pages with evidence of 

 the entire confusion of ideas which pervades his mind on this point, 

 but one extract must suffice, both as an indication of this confusion, 

 and as a fair example of the argument : 



" How much direct effect difference of climate, food, &c., pro- 

 duces on any being is extremely doubtful. My impression is that 

 the effect is extremely small in the case of animals, but perhaps 

 rather more in that of plants. We may, at least, safely conclude 

 that such influences cannot have produced the many striking and 

 complex co-adaptations of structure between one organic being 

 and another, which we see everywhere throughout nature. Some 

 little influence may be attributed to climate, food, &c. : thus, E. 

 Forbes speaks confidently that shells at their southern limit, and 

 when living in shallow water, are more brightly coloured than 

 those of the same species further north or from greater depths. 

 Gould believes that birds of the same species are more brightly 

 coloured under a clear atmosphere, than vs^hen living on islands 

 or near the coast. So with insects^ Wollaston is convinced that 

 residence near the sea affects their colours. Moquin-Tandon gives 

 a list of plants which when gTowing near the sea-shore have their 

 leaves in some degree fleshy, though not elsewhere fleshy. Se- 

 veral other such cases could be given." 



" The fact of varieties of one species, when they range into the 

 zone of habitation of other species, often acquiring in a very slight 

 degree some of the characters of such species, accords with our 

 view that species of all kinds are only well-marked and perma- 

 nent varieties. Thus the species of shells which are confined to 

 tropical and shallow seas are generally brighter coloured than 

 those confined to cold and deeper seas. The birds which are con- 

 fined to continents are according to Mr. Gould, brighter coloured 

 than those of islands. The insect species confined to &ea-coast&, 

 as every collector knows, are often brassy or lurid. Plants which 

 live exclusively on the sea-side are very apt to have fleshy leaves. 

 He who believes in the creation of each species, will have to say 

 that this shell, for instance, was created with bright colours for a 

 warm sea ; but that this other shell became bright coloured by 

 variation when it rano^ed into warmer or shallower waters," 



" When a variation is of the slightest use to a being, we cannot 

 tell how much of it to attribute to the accumulative action of 

 natural selection, and how much to the conditions of life. Thus, 



