Correspondence on Biology, etc. 



to do more than take very short theoretical steps till we get 

 more facts to rest upon. If you should happen to come across 

 any facts which seem to bear upon it, pray let me know. I 

 can find none but those I have referred to. 



I have just finished a chapter on male ornament and 

 display, which I trust will help to clear up that point.— 

 Believe me yours very faithfully, Alfred R. Wallace. 



To Db. W. B. Hemsley 



Frith Hill, Godalming. August 26, 1888. 



Dear Mr. Hemsley, — You are aware that Patrick Geddes 

 proposes to exclude Natural Selection in the origination of 

 thorns and spines, which he imputes to " diminishing vege- 

 tativeness " or '' ebbing vitality of the species." It has 

 occurred to me that insular floras should afford a test of 

 the correctness of this view, since in the absence of mam- 

 malia the protection of spines would be less needed. 



Your study of these floras will no doubt enable you to 

 answer a few questions on this point. Spines and thorns 

 are, I believe, usually abundant in arid regions of conti- 

 nents, especially in South Africa, where large herbivorous 

 mammals abound. Now, if the long-continued presence of 

 these mammals is a factor in the production of spines by 

 Natural Selection, they should be wholly or comparatively 

 absent in regions equally arid where there are no mam- 

 mals. The Galapagos seem to be such a case — also per- 

 haps some of the Sandwich Islands, and generally the 

 extra-tropical volcanic islands. Also Australia compara- 

 tively, and the highlands of Madagascar. 



Of course, the endemic species must be chiefly considered, 

 as they have had time to be modified by the conditions. If 

 you can give me the facts, or your general impression from 

 your study of these floras, I shall be much obliged. I see, 

 of course, many other objections to Geddes's theoiy, but 



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