CHAPTER XXII 



GEOGRAPHICAL DISTRIBUTION: GENERAL 



Our general outlook upon biological problems has been, and to 

 a great extent still is, principally governed by the theory of 

 natural selection — the mechanism by whose invention, and by 

 virtue of whose a priori reasonableness, Darwin Avas able to 

 render the immortal service of establishing the theory of evo- 

 lution. Few people nowadays would be found to give a complete 

 assent to the doctrine of natural selection, but though the pre- 

 mises are therefore weakened or destroyed, the conclusions 

 draw^n from them are still accepted with little or no question. 

 Somewhat to my surprise I have found many who no longer 

 accept natural selection as operative in evolution in a positive 

 (rather than negative) manner, but who are prepared to fight to 

 the death for conclusions that are essentially based upon it, such 

 as that species of small area are usually relics. 



When one comes to look at the history of the subject of geo- 

 graphical distribution, one soon reahses that since the impulse 

 which was first given to it by the acceptance of the theory of 

 natural selection has spent its force, little work of any import- 

 ance^ dealing with the broad general distribution of plants about 

 the world (as distinguished from their local distribution into 

 societies and associations occupying various types of habitat) 

 has been carried on. The limiting factor in progress at the present 

 time is the lack of a proper theoretical background from which 

 fruitful hypotheses may be derived. The facts of distribution 

 remain an insoluble problem so long as one cndeaA'ours to explain 

 them by the theory of natural selection, and the more that the 

 attempt is made, the greater is found to be the incompatibility 

 between theory and practice. The serious study of geographical 

 distribution has consequently been more and more neglected, 

 A\'hilst at the same time it has been admitted in a vague theoretical 

 way that no theory of evolution can stand wh'ch will not explain 

 the facts of dispersal. 



Chief among the deductions — consciously or unconsciously 



1 The last important work was probably that of Gi.ppy (44, 46, 47), and 

 it is to be noted that this work has led him to conclusions (expressed in his 

 Theory of Differentiation) diametrically opposed to the theory of Darwin. 



