238 THE PHILOSOPHY OF BIOLOGY 



of a multitude of small independent causes. Let us 

 grant this, and it still follows that the alternative of life 

 or death to multitudes of organisms depends not upon 

 their adaptability but upon minute un-co-ordinated 

 causes which have nothing to do with their morphology 

 or behaviour. These are instances among many others 

 which will occur to the field naturalist : they shorten 

 still further the time available for natural selection in 

 the shaping of species, for they reduce the material on 

 which this factor operates. 



The other result of our discussion is to indicate 

 that the problem of transformism of species is in 

 reality the problem of organic variability. Let us 

 assume that all the hypotheses of evolution are true : 

 that the environment may induce changes of mor- 

 phology and functioning in animals and plants, and 

 that these changes themselves — the actual acquire- 

 ments themselves, that is — are transmissible by 

 heredity. Let us assume that the germ-cells may be 

 affected by the environment, either the outer physical 

 environment, or the inner somatic environment, and 

 that mutations may thus arise. Let us assume that 

 mutations may be selected in some way, so that 

 specific discontinuities of structure — " individualised " 

 categories of organisms, or species — may thus come into 

 existence. Even then transformism is still as great a 

 problem as ever, for the question of the mode of origin 

 of these variations or modifications still presses for 



solution. 



The simplest possible cases that we can think of 

 present the most formidable difficulties. The muscles 

 of the shoulders and arms of the blacksmith become 

 bigger and stronger as the result of his activity. Why ? 

 We say that the increased katabolism of the tissues 

 causes a greater output of carbonic acid and other 



